ID: 35269461
Title: What's in a Gene? The Outstanding Diversity of MAPT.
Abstract: Tau protein is a microtubule-associated protein encoded by the MAPT gene that carries out a myriad of physiological functions and has been linked to certain pathologies collectively termed tauopathies, including Alzheimer's disease, frontotemporal dementia, Huntington's disease, progressive supranuclear palsy, etc. Alternative splicing is a physiological process by which cells generate several transcripts from one single gene and may in turn give rise to different proteins from the same gene. MAPT transcripts have been proven to be subjected to alternative splicing, generating six main isoforms in the central nervous system. Research throughout the years has demonstrated that the splicing landscape of the MAPT gene is far more complex than that, including at least exon skipping events, the use of 3' and 5' alternative splice sites and, as has been recently discovered, also intron retention. In addition, MAPT alternative splicing has been showed to be regulated spatially and developmentally, further evidencing the complexity of the gene's splicing regulation. It is unclear what would drive the need for the existence of so many isoforms encoded by the same gene, but a wide range of functions have been ascribed to these Tau isoforms, both in physiology and pathology. In this review we offer a comprehensive up-to-date exploration of the mechanisms leading to the outstanding diversity of isoforms expressed from the MAPT gene and the functions in which such isoforms are involved, including their potential role in the onset and development of tauopathies such as Alzheimer's disease.

ID: 37527763
Title: A panel of TDP-43-regulated splicing events verifies loss of TDP-43 function in amyotrophic lateral sclerosis brain tissue.
Abstract: TDP-43 dysfunction is a molecular hallmark of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). A major hypothesis of TDP-43 dysfunction in disease is the loss of normal nuclear function, resulting in impaired RNA regulation and the emergence of cryptic exons. Cryptic exons and differential exon usage are emerging as promising markers of lost TDP-43 function in addition to revealing biological pathways involved in neurodegeneration in ALS/FTD. In this brief report, we identified markers of TDP-43 loss of function by depleting TARDBP from post-mortem human brain pericytes, a manipulable in vitro primary human brain cell model, and identifying differential exon usage events with bulk RNA-sequencing analysis. We present these data in an interactive database (https://www.scotterlab.auckland.ac.nz/research-themes/tdp43-lof-db-v2/) together with seven other TDP-43-depletion datasets we meta-analysed previously, for user analysis of differential expression and splicing signatures. Differential exon usage events that were validated by qPCR were then compiled into a 'differential exon usage panel' with other well-established TDP-43 loss-of-function exon markers. This differential exon usage panel was investigated in ALS and control motor cortex tissue to verify whether, and to what extent, TDP-43 loss of function occurs in ALS. We find that profiles of TDP-43-regulated cryptic exons, changed exon usage and changed 3' UTR usage discriminate ALS brain tissue from controls, verifying that TDP-43 loss of function occurs in ALS. We propose that TDP-43-regulated splicing events that occur in brain tissue will have promise as predictors of disease.

ID: 37605276
Title: TDP-43-regulated cryptic RNAs accumulate in Alzheimer's disease brains.
Abstract: Inclusions of TAR DNA-binding protein 43 kDa (TDP-43) has been designated limbic-predominant, age-related TDP-43 encephalopathy (LATE), with or without co-occurrence of Alzheimer's disease (AD). Approximately, 30-70% AD cases present TDP-43 proteinopathy (AD-TDP), and a greater disease severity compared to AD patients without TDP-43 pathology. However, it remains unclear to what extent TDP-43 dysfunction is involved in AD pathogenesis. To investigate whether TDP-43 dysfunction is a prominent feature in AD-TDP cases, we evaluated whether non-conserved cryptic exons, which serve as a marker of TDP-43 dysfunction in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD-TDP), accumulate in AD-TDP brains. We assessed a cohort of 192 post-mortem brains from three different brain regions: amygdala, hippocampus, and frontal cortex. Following RNA and protein extraction, qRT-PCR and immunoassays were performed to quantify the accumulation of cryptic RNA targets and phosphorylated TDP-43 pathology, respectively. We detected the accumulation of misspliced cryptic or skiptic RNAs of STMN2, KCNQ2, UNC13A, CAMK2B, and SYT7 in the amygdala and hippocampus of AD-TDP cases. The topographic distribution of cryptic RNA accumulation mimicked that of phosphorylated TDP-43, regardless of TDP-43 subtype classification. Further, cryptic RNAs efficiently discriminated AD-TDP cases from controls. Overall, our results indicate that cryptic RNAs may represent an intriguing new therapeutic and diagnostic target in AD, and that methods aimed at detecting and measuring these species in patient biofluids could be used as a reliable tool to assess TDP-43 pathology in AD. Our work also raises the possibility that TDP-43 dysfunction and related changes in cryptic splicing could represent a common molecular mechanism shared between AD-TDP and FTLD-TDP.

ID: 38278991
Title: A fluid biomarker reveals loss of TDP-43 splicing repression in presymptomatic ALS-FTD.
Abstract: Although loss of TAR DNA-binding protein 43 kDa (TDP-43) splicing repression is well documented in postmortem tissues of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), whether this abnormality occurs during early-stage disease remains unresolved. Cryptic exon inclusion reflects loss of function of TDP-43, and thus detection of proteins containing cryptic exon-encoded neoepitopes in cerebrospinal fluid (CSF) or blood could reveal the earliest stages of TDP-43 dysregulation in patients. Here we use a newly characterized monoclonal antibody specific to a TDP-43-dependent cryptic epitope (encoded by the cryptic exon found in HDGFL2) to show that loss of TDP-43 splicing repression occurs in ALS-FTD, including in presymptomatic C9orf72 mutation carriers. Cryptic hepatoma-derived growth factor-like protein 2 (HDGFL2) accumulates in CSF at significantly higher levels in familial ALS-FTD and sporadic ALS compared with controls and is elevated earlier than neurofilament light and phosphorylated neurofilament heavy chain protein levels in familial disease. Cryptic HDGFL2 can also be detected in blood of individuals with ALS-FTD, including in presymptomatic C9orf72 mutation carriers, and accumulates at levels highly correlated with those in CSF. Our findings indicate that loss of TDP-43 cryptic splicing repression occurs early in disease progression, even presymptomatically, and that detection of the HDGFL2 cryptic neoepitope serves as a potential diagnostic biomarker for ALS, which should facilitate patient recruitment and measurement of target engagement in clinical trials.

ID: 38723906
Title: Molecular mechanisms linking loss of TDP-43 function to amyotrophic lateral sclerosis/frontotemporal dementia-related genes.
Abstract: Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are characterized by nuclear depletion and cytoplasmic aggregation of TAR DNA-binding protein-43 (TDP-43). TDP-43 plays a key role in regulating the splicing of numerous genes, including TARDBP. This review aims to delineate two aspects of ALS/FTD pathogenesis associated with TDP-43 function. First, we described novel mechanistic insights into the splicing of UNC13A, a TDP-43 target gene. Single nucleotide polymorphisms (SNPs) in UNC13A are the most common risk factors for ALS/FTD. We found that TDP-43 represses "cryptic exon" inclusion during UNC13A RNA splicing. A risk-associated SNP in this exon results in increased RNA levels of UNC13A retaining the cryptic exon. Second, we described the perturbation of the TDP-43 autoregulatory mechanism caused by age-related DNA demethylation. Aging is a major risk factor for sporadic ALS/FTD. Typically, TDP-43 levels are regulated via alternative splicing of TARDBP mRNA. This review focused on that TARDBP methylation is altered by aging, thereby disrupting TDP-43 autoregulation. It was found that demethylation reduces the efficiency of alternative splicing and increases TARDBP mRNA levels. Moreover, we demonstrated that, with aging, this region is demethylated in the human motor cortex and is associated with the early onset of ALS.

ID: 38940350
Title: Frontotemporal lobar degeneration targets brain regions linked to expression of recently evolved genes.
Abstract: In frontotemporal lobar degeneration (FTLD), pathological protein aggregation in specific brain regions is associated with declines in human-specialized social-emotional and language functions. In most patients, disease protein aggregates contain either TDP-43 (FTLD-TDP) or tau (FTLD-tau). Here, we explored whether FTLD-associated regional degeneration patterns relate to regional gene expression of human accelerated regions (HARs), conserved sequences that have undergone positive selection during recent human evolution. To this end, we used structural neuroimaging from patients with FTLD and human brain regional transcriptomic data from controls to identify genes expressed in FTLD-targeted brain regions. We then integrated primate comparative genomic data to test our hypothesis that FTLD targets brain regions linked to expression levels of recently evolved genes. In addition, we asked whether genes whose expression correlates with FTLD atrophy are enriched for genes that undergo cryptic splicing when TDP-43 function is impaired. We found that FTLD-TDP and FTLD-tau subtypes target brain regions with overlapping and distinct gene expression correlates, highlighting many genes linked to neuromodulatory functions. FTLD atrophy-correlated genes were strongly enriched for HARs. Atrophy-correlated genes in FTLD-TDP showed greater overlap with TDP-43 cryptic splicing genes and genes with more numerous TDP-43 binding sites compared with atrophy-correlated genes in FTLD-tau. Cryptic splicing genes were enriched for HAR genes, and vice versa, but this effect was due to the confounding influence of gene length. Analyses performed at the individual-patient level revealed that the expression of HAR genes and cryptically spliced genes within putative regions of disease onset differed across FTLD-TDP subtypes. Overall, our findings suggest that FTLD targets brain regions that have undergone recent evolutionary specialization and provide intriguing potential leads regarding the transcriptomic basis for selective vulnerability in distinct FTLD molecular-anatomical subtypes.

ID: 39181135
Title: Disruption of nuclear speckle integrity dysregulates RNA splicing in C9ORF72-FTD/ALS.
Abstract: Expansion of an intronic (GGGGCC)n repeat within the C9ORF72 gene is the most common genetic cause of both frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) (C9-FTD/ALS), characterized with aberrant repeat RNA foci and noncanonical translation-produced dipeptide repeat (DPR) protein inclusions. Here, we elucidate that the (GGGGCC)n repeat RNA co-localizes with nuclear speckles and alters their phase separation properties and granule dynamics. Moreover, the essential nuclear speckle scaffold protein SRRM2 is sequestered into the poly-GR cytoplasmic inclusions in the C9-FTD/ALS mouse model and patient postmortem tissues, exacerbating the nuclear speckle dysfunction. Impaired nuclear speckle integrity induces global exon skipping and intron retention in human iPSC-derived neurons and causes neuronal toxicity. Similar alternative splicing changes can be found in C9-FTD/ALS patient postmortem tissues. This work identified novel molecular mechanisms of global RNA splicing defects caused by impaired nuclear speckle function in C9-FTD/ALS and revealed novel potential biomarkers or therapeutic targets.

ID: 39361759
Title: Creation of de novo cryptic splicing for ALS and FTD precision medicine.
Abstract: Loss of function of the RNA-binding protein TDP-43 (TDP-LOF) is a hallmark of amyotrophic lateral sclerosis (ALS) and other neurodegenerative disorders. Here we describe TDP-REG, which exploits the specificity of cryptic splicing induced by TDP-LOF to drive protein expression when and where the disease process occurs. The SpliceNouveau algorithm combines deep learning with rational design to generate customizable cryptic splicing events within protein-coding sequences. We demonstrate that expression of TDP-REG reporters is tightly coupled to TDP-LOF in vitro and in vivo. TDP-REG enables genomic prime editing to ablate the UNC13A cryptic donor splice site specifically upon TDP-LOF. Finally, we design TDP-REG vectors encoding a TDP-43/Raver1 fusion protein that rescues key pathological cryptic splicing events, paving the way for the development of precision therapies for TDP43-related disorders.

ID: 40157355
Title: Seeded aggregation of TDP-43 induces its loss of function and reveals early pathological signatures.
Abstract: Neurodegeneration in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) results from both gain of toxicity and loss of normal function of the RNA-binding protein TDP-43, but their mechanistic connection remains unclear. Increasing evidence suggests that TDP-43 aggregates act as self-templating seeds, propagating pathology through the central nervous system via a prion-like cascade. We developed a robust TDP-43-seeding platform for quantitative assessment of TDP-43 aggregate uptake, cell-to-cell spreading, and loss of function within living cells, while they progress toward pathology. We show that both patient-derived and recombinant TDP-43 pathological aggregates were abundantly internalized by human neuron-like cells, efficiently recruited endogenous TDP-43, and formed cytoplasmic inclusions reminiscent of ALS/FTD pathology. Combining a fluorescent reporter of TDP-43 function with RNA sequencing and proteomics, we demonstrated aberrant cryptic splicing and a loss-of-function profile resulting from TDP-43-templated aggregation. Our data highlight known and novel pathological signatures in the context of seed-induced TDP-43 loss of function.

ID: 40478310
Title: Analysis of the splicing landscape of the frontal cortex in FTLD-TDP reveals subtype specific patterns and cryptic splicing.
Abstract: Dysregulation of TDP-43 as seen in TDP-43 proteinopathies leads to specific RNA splicing dysfunction. While discovery studies have explored novel TDP-43-driven splicing events in induced pluripotent stem cell (iPSC)-derived neurons and TDP-43 negative neuronal nuclei, transcriptome-wide investigations in frontotemporal lobar degeneration with TDP-43 aggregates (FTLD-TDP) brains remain unexplored. Such studies hold promise for identifying widespread novel and relevant splicing alterations in FTLD-TDP patient brains. We conducted the largest differential splicing analysis (DSA) using bulk short-read RNAseq data from frontal cortex (FCX) tissue of 127 FTLD-TDP (A, B, C, GRN and C9orf72 carriers) and 22 control subjects (Mayo Clinic Brain Bank), using Leafcutter. In addition, long-read bulk cDNA sequencing data were generated from FCX of 9 FTLD-TDP and 7 controls and human TARDBP wildtype and knock-down iPSC-derived neurons. Publicly available RNAseq data (MayoRNAseq, MSBB and ROSMAP studies) from Alzheimer's disease patients (AD) was also analyzed. Our DSA revealed extensive splicing alterations in FTLD-TDP patients with 1881 differentially spliced events, in 892 unique genes. When evaluating differences between FTLD-TDP subtypes, we found that C9orf72 repeat expansion carriers carried the most splicing alterations after accounting for differences in cell-type proportions. Focusing on cryptic splicing events, we identified STMN2 and ARHGAP32 as genes with the most abundant and differentially expressed cryptic exons between FTLD-TDP patients and controls in the brain, and we uncovered a set of 17 cryptic events consistently observed across studies, highlighting their potential relevance as biomarkers for TDP-43 proteinopathies. We also identified 16 cryptic events shared between FTLD-TDP and AD brains, suggesting potential common splicing dysregulation pathways in neurodegenerative diseases. Overall, this study provides a comprehensive map of splicing alterations in FTLD-TDP brains, revealing subtype-specific differences and identifying promising candidates for biomarker development and potential common pathogenic mechanisms between FTLD-TDP and AD.

ID: 40654715
Title: TDP-43 toxic gain of function links ALS, FTD and Alzheimer's Disease through splicing dysregulation.
Abstract: Loss of nuclear TDP-43 splicing activity is a common feature across neurodegenerative diseases including amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD), but its relevance to Alzheimer's disease (AD) remains unclear. Here, we show that TDP-43 pathology in AD is broadly associated with splicing abnormalities, including aberrant splicing of amyloid precursor protein (APP). TDP-43 drives the formation of elongated APP isoforms, disrupting alternative splicing across ALS, FTLD-TDP and AD, providing a compelling mechanism for a long-standing observation of APP isoform dysregulation. We further establish a mechanistic link between TDP-43, APP splicing, and Aβ pathology. Surprisingly, the disruption to alternative APP splicing is mediated by a toxic gain of cytoplasmic TDP-43 function, rather than loss of its nuclear role. Using proximity proteomics and base editing in human iPSC-derived neurons, we show that TDP-43 pathology causes cytoplasmic co-sequestration of splicing regulators SCAF11, SRSF5, and TIAL1. Knockdown of these regulators also results in APP mis-splicing and increased Aβ burden, without affecting other TDP-43 targets such as STMN2 or UNC13A. Together, our findings suggest that TDP-43-mediated splicing dysfunction upstream of APP contributes to the pathogenesis of seemingly disparate neurodegenerative diseases, uniting AD and ALS/FTLD-TDP through a shared molecular mechanism.

ID: 40783910
Title: Brain transcriptomics highlight abundant gene expression and splicing alterations in non-neuronal cells in aFTLD-U.
Abstract: Atypical frontotemporal lobar degeneration with ubiquitin-positive inclusions (aFTLD-U) is a rare cause of frontotemporal lobar degeneration (FTLD), characterized postmortem by neuronal inclusions of the FET family of proteins (FTLD-FET). The recent discovery of TAF15 amyloid filaments in aFTLD-U brains represents a significant step toward improved diagnostic and therapeutic strategies. However, our understanding of the etiology of this FTLD subtype remains limited, which severely hampers translational research efforts. To explore the transcriptomic changes in aFTLD-U, we performed bulk RNA sequencing on the frontal cortex tissue of 21 aFTLD-U patients and 20 control individuals. Cell-type deconvolution revealed loss of excitatory neurons and a higher proportion of astrocytes in aFTLD-U relative to controls. Differential gene expression and co-expression network analysis, adjusted for the shift in cell-type proportions, showed dysregulation of mitochondrial pathways, transcriptional regulators, and upregulation of the Sonic hedgehog (Shh) pathway, including the GLI1 transcription factor, in aFTLD-U. Overall, oligodendrocyte and astrocyte-enriched genes were significantly over-represented among the differentially expressed genes. Differential splicing analysis confirmed the dysregulation of non-neuronal cell types with significant splicing alterations, particularly in oligodendrocyte-enriched genes, including myelin basic protein (MBP), a crucial component of myelin. Immunohistochemistry in frontal cortex brain tissue also showed reduced myelin levels in aFTLD-U patients compared to controls. Together, these findings highlight a central role for glial cells, particularly astrocytes and oligodendrocytes, in the pathogenesis of aFTLD-U, with disruptions in mitochondrial activity, RNA metabolism, Shh signaling, and myelination as possible disease mechanisms. This study offers the first transcriptomic insight into aFTLD-U and presents new avenues for research into FTLD-FET.

ID: 40790269
Title: Aberrant splicing exonizes C9orf72 repeat expansion in ALS/FTD.
Abstract: A nucleotide repeat expansion (NRE) (GGGGCC)n within the first annotated intron of the C9orf72 (C9) gene is a common cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). While previous studies have shown that C9 NRE produces several toxic dipeptide repeat (DPR) proteins, the mechanism by which an intronic RNA segment can access the cytoplasmic translation machinery remains unclear. By selectively capturing and sequencing NRE-containing RNAs (NRE-capture-seq) from patient-derived fibroblasts and neurons, we found that, in contrast to previous models, C9 NRE is retained as part of an extended exon 1 due to the usage of various downstream alternative 5' splice sites. These aberrant splice isoforms accumulate in C9-ALS/FTD brains, and their production is promoted by serine/arginine-rich splicing factor 1 (SRSF1). Antisense oligonucleotides targeting either SRSF1 or the aberrant C9 splice isoforms reduced the levels of DPR. Together, our findings revealed a crucial role of aberrant splicing in the biogenesis of NRE-containing RNAs and demonstrated potential therapeutic strategies to target these pathogenic transcripts.

ID: 40913764
Title: A single-cell, long-read, isoform-resolved case-control study of FTD reveals cell-type-specific and broad splicing dysregulation in human brain.
Abstract: Progranulin-deficient frontotemporal dementia (GRN-FTD) is a major cause of familial FTD with TAR DNA-binding protein 43 (TDP-43) pathology, which is linked to exon dysregulation. However, little is known about this dysregulation in glial and neuronal cells. Here, using splice-junction-covering enrichment probes, we introduce single-nuclei long-read RNA sequencing 2 (SnISOr-Seq2), targeting 3,630 high-interest genes without loss of precision, and complete the first single-cell, long-read-resolved case-control study for neurodegeneration. Exons affected by FTD-associated skipping are shorter than those whose inclusion is increased. Up to 30% of cell-(sub)type-specific splicing dysregulation is masked by other cell types or cortical layers. Surprisingly, strong splicing dysregulation events can occur in select but not all cell types. In some cases, a cell type switches in FTD to the splicing pattern of a different cell type. In addition, in separate GRN-FTD samples, the more FTD-prone frontal cortex exhibits more FTD-associated splicing patterns than the occipital cortex. Our methodologies are widely applicable to brain and other diseases.

ID: 41120751
Title: TDP-43 loss induces cryptic polyadenylation in ALS/FTD.
Abstract: Nuclear depletion and cytoplasmic aggregation of the RNA-binding protein TDP-43 are cellular hallmarks of amyotrophic lateral sclerosis (ALS). TDP-43 nuclear loss causes de-repression of cryptic exons, yet cryptic alternative polyadenylation (APA) events have been largely overlooked. In this study, we developed a bioinformatic pipeline to reliably identify alternative last exons, 3' untranslated region (3'UTR) extensions and intronic polyadenylation APA event types, and we identified cryptic APA sites induced by TDP-43 loss in induced pluripotent stem cell (iPSC)-derived neurons. TDP-43 binding sites are enriched at sites of these cryptic events, and TDP-43 can both repress and enhance APA. All categories of cryptic APA were also identified in ALS and frontotemporal dementia (FTD) postmortem brain tissue. RNA sequencing (RNA-seq), thiol(SH)-linked alkylation for the metabolic sequencing of RNA (SLAM-seq) and ribosome profiling (Ribo-seq) revealed that distinct cryptic APA categories have different downstream effects on transcript levels and that cryptic 3'UTR extensions can increase RNA stability, leading to increased translation. In summary, we demonstrate that TDP-43 nuclear depletion induces cryptic APA, expanding the palette of known consequences of TDP-43.

ID: 41174170
Title: TDP-43-dependent mis-splicing of KCNQ2 triggers intrinsic neuronal hyperexcitability in ALS/FTD.
Abstract: Motor neuron hyperexcitability is a broadly observed yet poorly understood feature of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Nuclear depletion and cytoplasmic aggregation of the RNA splicing protein TAR DNA-binding protein 43 (TDP-43) are observed in most ALS and FTD patients. Here we show that TDP-43 dysfunction causes mis-splicing of KCNQ2, which encodes a voltage-gated potassium channel (Kv7.2) that regulates neuronal excitability. Using iPSC-derived neurons and postmortem ALS/FTD brain and spinal cord tissue we find widespread, disease-specific and TDP-43-specific skipping of an exon encoding the KCNQ2 pore domain. The mis-spliced mRNA escapes degradation and is translated into a nonfunctional protein with severely reduced ion conductance that aggregates in the endoplasmic reticulum and causes intrinsic hyperexcitability in ALS neuronal models. This event, which correlates with higher phosphorylated TDP-43 levels and earlier age of disease onset in patients, can be rescued by splice-modulating antisense oligonucleotides that dampen hyperexcitability in induced pluripotent stem cell cortical neurons and spinal motor neurons with TDP-43 depletion. Our work reveals that nuclear TDP-43 maintains the fidelity of KCNQ2 expression and function and provides a mechanistic link between established excitability disruption in ALS/FTD patients and TDP-43 dysfunction.

ID: 41523913
Title: RNA-Seq of Cultured Peripheral Blood Lymphocytes Improves Identification of Cryptic Splicing Defects in Rare Disease Diagnostics.
Abstract: Accurate identification of the genetic determinants of rare diseases is essential for effective recurrence-risk management and informed reproductive decision-making. Although whole-exome sequencing (WES) and whole-genome sequencing (WGS) have significantly improved diagnostic capabilities, a subset of affected families still receives no definitive molecular diagnosis. RNA sequencing (RNA-seq) has emerged as a promising complementary diagnostic tool, yet its clinical implementation in the context of preconception genetic counseling remains underexplored. We used phytohemagglutinin-activated peripheral blood cells (PHACs) as a robust RNA source and enhanced conventional RNA-seq through the integration of three analytical innovations: (1) transcript isoform distribution (TID) analysis, (2) realignment against the MANE (Matched Annotation from NCBI and EMBL-EBI) reference transcriptome, and (3) pharmacological induction-based cryptic splicing detection. This optimized pipeline was applied to 55 rare-disease families with negative WES/WGS results who were undergoing preconception genetic counseling. Based on prior evaluations, families were grouped as VUS (n = 7), suspected-gene/variant-negative (n = 10), and unsolved/no-candidate (n = 38). PHACs showed reduced interindividual variability and higher RNA integrity than fresh PBMCs (median RIN: 9.77 vs. 8.97; p < 0.0001). The optimized workflow improved diagnostic yield by 2.2-fold (20% vs. 9%). Stratified analysis revealed positive rates of 71% (VUS), 40% (suspected-gene/variant-negative), and 5.2% (unsolved/no-candidate). Among the 11 positive cases, 10 received definitive diagnoses, leading to diverse reproductive decisions. This enhanced RNA-seq workflow provides a clinically applicable and scalable strategy for improving molecular diagnostics in reproductive and preconception settings, offering a valuable model for future clinical transcriptomics.

ID: 41542389
Title: TDP-43 dysfunction leads to the accumulation of cryptic transposable element-derived exons, crypTEs, in iPSC derived neurons and ALS/FTD patient tissues.
Abstract: TDP-43 is an RNA and DNA binding protein that plays major roles in regulating RNA processing. In particular, TDP-43 dysfunction leads to the accumulation of cryptic splice isoforms that result from improperly spliced mRNAs. In addition to its role in regulating splicing, TDP-43 is also known to regulate the expression of transposable elements (TEs). TEs are mobile genetic elements which comprise a significant proportion of the human genome, but are normally silenced in healthy somatic cells. TEs are interspersed throughout the genome, both in gene-depleted regions and within gene introns and gene regulatory sequences. We used optimized long-read RNA sequencing assays to generate catalogs of mis-spliced and mis-expressed genes and TEs in human neurons depleted for TDP-43. In addition to known TDP-43 driven cryptic isoforms, we identified hundreds of TDP-43 dependent spliced RNAs that form cryptic gene-TE fusion events as a result of mis-splicing of TE sequences into gene transcripts. Among these TDP-43 dependent cryptic gene-TE transcripts (crypTEs), we found: TEs that provide alternate gene promoters/5'UTRs, TEs that act as cassette exons inside host gene mRNAs, as well as TEs that provide alternate transcript 3' ends. These cryptic gene-TE fusions are predicted to induce aberrant expression of ALS relevant genes, nonsense mediated decay (NMD) products, as well as novel peptides from gene-TE fusions within the gene coding sequence. Using coupled long-read RNA (Iso-seq) and single-nucleus (snRNA-seq) profiles from postmortem ALS tissues, we further verified that many of these crypTE transcripts are enriched in frontal cortex samples from ALS donors with cognitive involvement (ALSci) and associated with altered expression of those genes in deep layer cortical excitatory neurons. In short, TDP-43 dependent crypTEs greatly expand the catalogs of TDP-43 dependent cryptic splice isoforms and represent a novel mechanism by which TE dysregulation impacts ALS.

ID: 41565639
Title: From TDP-43/RNA complex formation to disease-linked TDP-43 aggregation through a structural and cellular approach.
Abstract: Many RNA-binding proteins (RBP) have been associated to several neurodegenerative diseases for which RBP-rich cytoplasmic inclusions represent a major histological hallmark. However, among RBPs, the occurrence with which TDP-43, a nuclear mRNA-binding protein, is detected in cytoplasmic inclusions is exceptionally high. To unravel the underlying mechanisms, we focus our analysis on the structured N-terminal domain (NTD) of TDP-43, which is distinct among RBPs as this domain mostly initiates TDP-43 homotypic interactions. Through an in depth structural analysis, we successively show that the cooperative binding of TDP-43 along long GU-rich intronic sequences antagonizes NTD/NTD interactions between adjacent TDP-43 along mRNA. In contrast, the TDP-43 cooperativity facilitates NTD/NTD interactions between TDP-43 located on distinct GU-rich sequences. We hypothesize that NTD/NTD interactions between distinct GU-rich sequences efficiently allow the compaction of long introns in neurons under physiological conditions. However, when the binding of TDP-43 to RNA is discontinuous because of a lack of cooperativity, aberrant NTD/NTD interactions between adjacent TDP-43 take place, promoting the aggregation of TDP-43 RRMs (RNA Recognition Motifs) under stress conditions. Altogether, we provide a detailed view of the physiological assembly of TDP-43 on introns and the putative weaknesses of TDP-43 that makes it distinct in its propensity for aggregation compared to other RBPs.

ID: 41637622
Title: Aberrant Splicing Signatures Underpin Oligodendrocyte Damage in ALS and Neuron Loss in FTD.
Abstract: Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are two severe diseases sharing similar genetic, pathological, and clinical features, including TDP-43 pathology. However, differences in molecular changes between ALS and FTD remain elusive. Here, integrating large sets of bulk and single-nucleus RNA-seq from ALS/FTD patients revealed expression and splicing changes indicating more severe oligodendrocyte damage in ALS than FTD, and more significant neuron loss in FTD. Specifically, we identified 31 oligodendrocyte-specific and 507 neuron-specific aberrant splicing junctions as potential biomarkers with robust classification performance, and experimentally validated a novel target in patient tissues. Moreover, we found that abnormally spliced transcripts produced de novo peptides in patients' cerebrospinal fluids. Importantly, we further identified the targets of TDP-43 in glial cells and decoded the differential RNA-binding protein (RBP) contexts of TDP-43-regulated aberrant splicing. These findings uncover that ALS and FTD patients have distinct dysfunctional cell populations harboring specific aberrant splicing signatures, suggesting varying cellular impacts and providing potential biomarkers and insights into molecular mechanisms underlying ALS/FTD.

ID: 41720774
Title: A neurotoxic cryptic peptide arising from TDP-43-dependent cryptic splicing of PKN1.
Abstract: Dysfunction of transactive response DNA-binding protein 43 (TDP-43) drives neurodegeneration in amyotrophic lateral sclerosis (ALS) and Alzheimer's disease (AD), in part through inducing aberrant RNA splicing. However, whether such mis-splicing yields stable, pathogenic proteins remains unclear. Here, we identify a TDP-43-repressed cryptic exon in Protein kinase N1 (PKN1), designated PKN1-5a1, which is activated in ALS patient brains and introduces a premature termination codon. This aberrant transcript escapes nonsense-mediated decay and is translated into a truncated peptide, PKN1-N207 (PKN207), detectable in AD brains with TDP-43 pathology. In mice, PKN207 impairs cognition, memory, and synaptic plasticity. Our findings demonstrate that TDP-43 loss-induced cryptic splicing can generate stable neurotoxic polypeptides, revealing a peptide-mediated mechanism in TDP-43 proteinopathies.

ID: 41726928
Title: Distinct tau filament folds in familial frontotemporal dementia due to the MAPT S305I mutation.
Abstract: Frontotemporal lobar degeneration with tau inclusions (FTLD-tau) comprise a class of fatal heterogeneous neurodegenerative diseases. Approximately 10% arise from pathogenic MAPT mutations and often cause severe, early-onset disease with pathology that is distinct yet partially overlapping with sporadic cases. Here, we evaluated post-mortem tissue from a patient with FTLD-tau due to MAPT S305I showing neuropathology most consistent with argyrophilic grain disease (AGD), a prevalent limbic tauopathy of aging. Structures determined by cryo-electron microscopy reveal tau filament folds that differ from those found in sporadic AGD or other tauopathies and feature a 4-layer architecture stabilized by the Ile substitution within its core. Comparative structural analysis reveals conserved motifs are shared among AGD, corticobasal degeneration, and MAPT P301T. A well-defined density stacks along a cationic cleft, indicative of a bound RNA-like polyanion or small-molecule. In vitro analysis shows the S305I mutation promotes fibrilization relative to normal tau. These results demonstrate that MAPT S305I stabilizes a distinct aggregation-prone tau fold that likely contributes to disease pathology and heterogeneity beyond its known splicing defects, and underscore potential limitations of using the most pathologically similar genetic form as a model for sporadic FTLD-tau.

ID: 41761273
Title: TDP-43-driven alternative splicing of UQCRC2 modulates mitochondrial bioenergetics.
Abstract: TAR DNA-binding protein 43 (TDP-43) is a nuclear RNA-binding protein. It has emerged as a key regulator of RNA processing, such as alternative splicing events, which are essential for cellular homeostasis. The mislocalization and aggregation of TDP-43 are closely associated with mitochondrial dysfunction. However, the mechanisms by which the formation TDP-43 contributes to mitochondrial impairment remain poorly understood. In this study, we confirmed that the TDP-43 loss leads to dramatic alterations in mitochondrial morphology and a significant reduction in respiratory capacity. Further analysis of oxidative phosphorylation (OXPHOS) complex assembly revealed a selective disruption of complex III activity. Notably, the core complex III subunit UQCRC2 was significantly decreased as long as TDP-43 was knocked down. The transcript analysis showed that the loss of TDP-43 results in aberrant alternative splicing of the nuclear-encoded UQCRC2 transcript. In parallel, this mis-splicing event was consistently observed in both dividing cells, including HEK293T, and in the neuroblastoma cell line SH-SY5Y, suggesting that TDP-43-mediated regulation of UQCRC2 splicing can be potentially conserved across a wide range of cell types. These findings indicate a novel role for TDP-43 in maintaining mitochondrial integrity via regulation of UQCRC2 expression and splicing, providing mechanistic insight into how dysregulated RNA processing contributes to mitochondrial bioenergetic deficits.

ID: 41845971
Title: The role of TDP-43 fragments in regular cellular functions and homeostatic failure.
Abstract: Amyotrophic lateral sclerosis (ALS) is characterized by the progressive degeneration of motor neurons, leading to severe muscle weakness, loss of voluntary movement, and respiratory failure. A widely noted feature of the disease is the presence of TDP-43 proteinopathies. Under homeostatic conditions, the RNA/DNA-binding protein TDP-43 mainly resides in the nucleus, where it functions to regulate gene expression, controlling not only RNA transcription and splicing, but also stability and transport to the cytoplasm. Upon the arrival at ribosomes, TDP-43 may further moderate translation, acting as a global repressor of protein synthesis. However, in over 95% of ALS cases, TDP-43 mislocalises from the nucleus to the cytoplasm, where it enriches in cytoplasmic inclusions that are marked by the presence of misfolded, ubiquitinated, phosphorylated and fragmented protein species of TDP-43. Although recent studies have tried to untangle the relationship between TDP fragments on the one hand, and cytotoxicity as well as neurodegeneration on the other, the results are still a matter of debate. Here, we review our current understanding of the different TDP fragments derived from proteolytic cleavage as well as alternative splicing, addressing the different N-terminal and C-terminal species and evaluating differences in rodent and primate models. We focus our analysis on potential homeostatic functions of TDP fragments in the context of viral infections and myelination control, which could be pivotally interconnected. The findings illustrate several facets of fragmented TDP-43 protein species in scenarios of enhanced cellular stress. Gaining a detailed understanding could help to reveal new treatment options for ALS and other TDP-43 proteinopathies.

ID: 41875078
Title: A quantitative cell-based reporter links TDP-43 aggregation and dysfunction to define pathogenic mechanisms.
Abstract: TDP-43 pathology is a hallmark of fatal neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and limbic-predominant age-related TDP-43-encephalopathy (LATE). In affected patients, cytoplasmic TDP-43 aggregates are accompanied by disruption of its normal nuclear localization and function. Because TDP-43 is an RNA binding protein that controls transcript processing, including repression of cryptic exon splicing, its loss leads to dysregulation of gene expression. Despite its central significance in disease, the connection between TDP-43 aggregation and dysfunction remains poorly understood, and models to study the underlying mechanisms are limited. Here, we characterize a robust and quantitative cell-based reporter that captures both aggregation and the resulting loss of function. Using this human biosensor cell line, we show that aggregation initiated by prion-like seeding drives progressive depletion of nuclear TDP-43 and induces signature features of diminished TDP-43 activity, such as increased DNA damage and activation of cryptic exon splicing. We find that aggregate seeding also induces cryptic exon splicing in human neurons implying that this pathological link extends to disease-relevant models. The seeding model provides a platform for dissecting mechanisms that underlie TDP-43 pathology and for identifying factors that modulate the aggregation-to-dysfunction transition. Our data shows that aggregate seeding impacts TDP-43 autoregulation, initiating a toxic feed-forward mechanism that disrupts TDP-43 homeostasis. Furthermore, reducing ataxin-2 levels decreases aggregation and restores TDP-43 activity. Together, these findings reveal a molecularly guided strategy to directly impact TDP-43 activity by decreasing its misfolding and aggregation, highlighting approaches to prevent TDP-43 dysfunction and mitigate toxicity under pathological conditions.

ID: 41908332
Title: Enhancer RNA-mediated transcriptional regulation of TDP-43 during early neural lineage specification.
Abstract: TAR DNA-binding protein 43 (TDP-43) is a DNA- and RNA-binding protein that regulates gene expression by modulating transcription and RNA processing. It plays pivotal roles in neuronal development and function, and its mislocalization and aggregation are major pathological features of several neurodegenerative diseases. However, the regulatory mechanisms that control Tdp-43 expression and activity during the transition from embryonic stem cells (ESCs) to neural progenitor cells (NPCs) remain poorly understood. Through integrative epigenomic and transcriptomic analyses, we identified multiple intergenic and intragenic enhancers within and around the Tdp-43 locus that generate enhancer RNAs (eRNAs). These eRNAs exhibit dynamic, region-specific expression changes and modulate Tdp-43 transcription in a stage- and context-dependent manner. Specifically, a subset of eRNAs was highly expressed in ESCs and downregulated upon differentiation, while others were selectively retained or induced in NPCs, paralleling changes in enhancer usage and histone modification states. Targeted knockdown of these eRNAs decreased Tdp-43 expression and was accompanied by changes in the expression of pluripotency- and lineage-associated markers, without implying direct control over full differentiation trajectories. These findings uncover a previously unrecognized aspect of Tdp-43 transcriptional regulation and highlight the significance of enhancer dynamics in the epigenetic regulation of TDP-43 expression during early lineage specification.

ID: 41943580
Title: DCPS modulates TDP-43-linked neurodegeneration through P-body-mediated RNA decay.
Abstract: The proteinopathy of the RNA-binding protein TDP-43, characterized by nuclear clearance and cytoplasmic inclusion, is a hallmark of multiple neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and Alzheimer's disease (AD). Through CRISPR interference (CRISPRi) screening in human neurons, we identified the decapping scavenger enzyme (DCPS) as a novel genetic modifier of TDP-43 loss-of-function (LOF)-mediated neurotoxicity. Our findings reveal that TDP-43 LOF leads to aberrant mRNA degradation via dysregulating the properties and activity of processing bodies (P-bodies). TDP-43 interacts with P-body component proteins, potentially influencing their dynamic equilibrium and assembly into ribonucleoprotein (RNP) granules. Loss of TDP-43 hyperactivates P-bodies, increasing mRNA association and RNA decay. Reducing DCPS restores P-body integrity and RNA turnover, ultimately improving neuronal survival. Overall, this study highlights a novel role of TDP-43 in RNA processing through P-body regulation and identifies DCPS as a potential therapeutic target for TDP-43 proteinopathy-related neurodegenerative diseases.

ID: 41962593
Title: Mechanistic research and therapeutic prospects of alternative splicing in neurodegenerative diseases.
Abstract: One essential post-transcriptional regulatory mechanism that increases protein diversity in eukaryotes is alternative splicing. This process is crucial for maintaining nervous system function and is highly active in neurons. Dysregulation of alternative splicing is a common pathogenic factor in many neurodegenerative diseases. For example, splicing variants of tau protein and amyloid precursor protein are implicated in Alzheimer's disease; aberrant splicing of α-synuclein (SNCA) and upregulation of specific transcript variants of the Parkin (PARK2) gene occurs in Parkinson's disease; and aberrant splicing of Stathmin-2 (STMN2) pre-mRNA leads to the loss of axonal maintenance proteins in amyotrophic lateral sclerosis and frontotemporal dementia. This process is precisely regulated by trans-acting factors, a class of RBPs that specifically recognize and bind to cis-acting elements on precursor mRNA (pre-mRNA). These factors are primarily categorized into two major groups: serine/arginine-rich (SR) proteins and heterogeneous nuclear ribonucleoproteins (hnRNPs). Although hnRNPs and SR proteins have been shown to regulate neuronal alternative splicing, their complex regulatory networks and associated disease mechanisms remain incompletely understood, hindering the development of targeted therapies. This review summarizes the molecular mechanisms of alternative splicing and its regulatory features in neurodegenerative diseases. It also summarizes recent advances in splicing-based therapies and biomarkers, providing insights into disease mechanisms and therapeutic development.

ID: 41969219
Title: An ALS-associated mutation in the C-terminal α-helix of TDP-43 uncouples condensate formation and amyloid assembly.
Abstract: TAR DNA-binding protein 43 (TDP-43) plays a critical role in RNA metabolism and is incorporated into biomolecular condensates called stress granules. In amyotrophic lateral sclerosis (ALS) and several other neurodegenerative disorders, TDP-43 undergoes aberrant phase transitions, forming insoluble amyloid aggregates, including fibrils composed of solely its intrinsically disordered C-terminal domain (CTD). Despite its central role in disease, the conformational dynamics of the CTD remain poorly understood due to its heterogeneous and transient conformational landscape. Here, we employ native ion mobility-mass spectrometry (IM-MS) using nanopipette sub-micron nano electrospray ionization (nanoESI) emitters to characterize the conformational landscape of wild-type and ALS-associated TDP-43 CTD variants (Q331K and R361S) under different solution conditions. Our data suggest that mutations and salt concentration modulate the CTD's conformations. Combined with thioflavin T fluorescence, light scattering, and microscopy, we reveal that these conformational shifts correlate with altered amyloid assembly kinetics and propensity to form condensates. Notably, the Q331K variant, which has a mutation in the transient α-helical region in the CTD, has reduced propensity to form biomolecular condensates but can undergo amyloid assembly in the absence of condensate formation, suggesting that sequence alterations in this α-helical region can tune the molecular mechanism of amyloid assembly. This study demonstrates the power of IM-MS in probing disordered proteins and reveals mechanistic insights into how disease-associated mutations differentially tune TDP-43 CTD amyloid assembly mechanisms.

ID: 42013476
Title: Cryptic Splicing in ALS: From Driving Disease Progression to Unlocking Novel Therapeutics.
Abstract: TDP-43 is an RNA-binding protein that regulates multiple aspects of RNA processing, and its mislocalization from the nucleus to the cytoplasm is a defining feature of amyotrophic lateral sclerosis (ALS). While both loss- and gain-of-function mechanisms contribute to disease, the discovery of cryptic splicing has shed light on the downstream consequences of TDP-43 nuclear clearance for neuronal health. Here, we highlight how loss of nuclear TDP-43 can drive a cascade of events that lead to the impairment of cellular proteostasis and result in a positive feedback loop that perpetuates neuronal dysfunction. This sustains the appearance of cryptic splicing events in genes that are involved in key pathways for the maintenance of axonal homeostasis and synaptic transmission. In contrast to their detrimental effects on neuronal health, cryptic splicing mechanisms may be harnessed to develop novel therapeutic strategies, unprecedentedly expanding the availability of therapeutic avenues for TDP-43 proteinopathies.

ID: 42135750
Title: Maintenance and disruption of the physiological dimer structure of TDP-43 in amyotrophic lateral sclerosis and frontotemporal lobar degeneration.
Abstract: Transactive response DNA-binding protein of 43 kDa (TDP-43) is an essential regulator of RNA metabolism, playing a pivotal role in splicing, transport, and stability. While its cytoplasmic aggregation is the pathological hallmark of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD), recent evidence suggests that the earliest pathogenic event is the disruption of its physiological homodimeric structure. Under healthy conditions, TDP-43 forms dimers via its N-terminal domain, a configuration that is crucial for its nuclear solubility and cooperative RNA binding. In this review, we propose the "Molecular Zipper" hypothesis to describe the maintenance of TDP-43 structural homeostasis. In this framework, the N-terminal domain acts as a stabilizing "NTD-mediated anchor" that keeps the protein in a functional, "zipped" dimeric state, effectively sequestering its aggregation-prone C-terminal regions. Pathogenic triggers-including genetic mutations, aberrant post-translational modifications such as phosphorylation and acetylation, and environmental stressors-can "unzip" this structure, leading to the formation of pathogenic monomers. These pathogenic monomers show increased propensity for cytoplasmic mislocalization and recruit wild-type protein into aggregates through a prion-like seeded aggregation mechanism, culminating in nuclear functional loss and cytoplasmic gain-of-toxicity. We further evaluate the emerging diagnostic landscape, focusing on methods to monitor the dimer-to-monomer ratio. Integrating prior biochemical data on TDP-43 dimerization with structural modeling enables a more coherent account of the transition from the physiological dimer to pathological conformers. The Molecular Zipper framework offers a conceptual foundation for reconciling existing experimental findings and for guiding future studies on early structural changes in TDP-43 proteinopathy.

ID: 42135847
Title: TDP-43: [GU]-ardian of the transcriptome.
Abstract: TDP-43 is a ubiquitously expressed, primarily nuclear DNA/RNA-binding protein implicated in neurodegenerative diseases including amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and Alzheimer's disease (AD). In this review, we examine the structure and regulation of TDP-43, how these features influence its localization and functional activity, and how their disruption may contribute to disease. Among TDP-43's diverse functions, splicing repression of nonconserved RNA sequences termed cryptic exons has emerged as especially central to human disease. TDP-43 nuclear depletion and cytoplasmic aggregation are well-established pathological features in affected neurons and glia of neurodegenerative diseases, and accumulating evidence suggests that loss of TDP-43-mediated splicing repression occurs presymptomatically in disease. Advances in RNA-sequencing have enabled systematic identification of cryptic exon inclusion as a sensitive marker of TDP-43 dysfunction. Here, we synthesize current knowledge of TDP-43 biology and curate datasets from human tissues and experimental models, focusing on cryptic splicing to provide a resource for leveraging cryptic exon biology to better understand, detect, and target TDP-43 dysfunction.

ID: 42220212
Title: Multiple mechanisms lead to loss-of-function effects of pathogenic SARS2 variants.
Abstract: Seryl-tRNA synthetase 2 (SARS2) encodes the enzyme responsible for charging tRNA with serine in the mitochondria. SARS2 has been associated with a spectrum of recessive diseases including HUPRA syndrome and progressive spastic paresis. Previous studies showed that pathogenic SARS2 variants cause decreased tRNA charging; however, the mechanism by which specific variants lead to distinct recessive phenotypes has not been defined. To address this lack of knowledge, we studied an allelic series of 11 pathogenic SARS2 variants for differential effects on mitochondrial function. These efforts revealed compelling variant-dependent effects on oxygen consumption that will be useful for genotype-phenotype correlations. Interestingly, certain variants (including the most commonly detected pathogenic SARS2 variant, R402H) did not affect mitochondrial function in our model system. Computational and functional studies revealed that two missense variants in exon 13 (D390G and R402H) reduce exon inclusion, suggesting loss-of-function effects via impaired transcript processing. Overall, this study expands our understanding of SARS2 biology, reveals differential effects that pathogenic variants have on SARS2 function, and provides the foundation for defining the clinical heterogeneity of patient phenotypes.

ID: 42234776
Title: Cryptic splicing in synaptic and membrane excitability genes links TDP-43 loss to neuronal dysfunction.
Abstract: TAR DNA binding protein 43 (TDP-43) pathology is a defining pathological hallmark of multiple neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). A major feature of TDP-43 pathology is its nuclear depletion, leading to the aberrant inclusion of cryptic exons during RNA splicing. STMN2 and UNC13A have emerged as prominent TDP-43 splicing targets, but the broader impact of TDP-43-dependent cryptic splicing on neuronal function remains unclear. Here, we report previously unidentified TDP-43 splicing targets critical for membrane excitability and synaptic function, including KALRN, RAP1GAP, SYT7, and KCNQ2. Using human stem cell-derived neurons, we showed that TDP-43 reduction induces cryptic splicing and down-regulation of these genes, resulting in impaired excitability and synaptic transmission. In postmortem brains from patients with FTD, these cryptic splicing events occurred selectively in neurons with TDP-43 pathology. Suppressing individual cryptic splicing events using antisense oligonucleotides partially restored neuronal function, and combined targeting almost fully rescued the synaptic deficit caused by TDP-43 loss. Together, our findings provide evidence that cryptic splicing in these synaptic and membrane excitability genes is not only a downstream marker but instead a direct driver of neuronal dysfunction, establishing a mechanistic link between TDP-43 pathology and neurodegeneration in ALS and FTD.

ID: 42239060
Title: TDP-43 Sustains Satellite Cells to Maintain and Regenerate Skeletal Muscle.
Abstract: Skeletal muscle satellite cells, residing between the myofiber plasma membrane and the surrounding basement membrane, maintain and repair skeletal muscle throughout life. Typically quiescent, satellite cells can transition into a reversible alert state (G Alert ) that primes them for rapid activation to maintain or repair muscle. From G Alert , SCs can either re-enter quiescence or commit to the cell cycle, expand, and differentiate to fuse with existing regenerating myofibers. Exit from quiescence requires extensive post-transcriptional remodeling, including changes in RNA processing and RNA-binding protein activity. We show that TDP-43, an RNA binding protein, is essential for SC maintenance and muscle repair. Conditional deletion of TDP-43 in SCs caused a consistent and progressive loss of G Alert SCs even in uninjured muscle, leading to depletion of the SC pool. TDP-43 haploinsufficiency was sufficient to impair SC maintenance, indicating that both alleles are required. Integrative analysis suggests that TDP-43 supports expression of stress response-associated transcripts during the quiescent-to-G Alert transition, and that failure to mount this response contributes to SC apoptosis. Thus, we identified TDP-43 as a critical regulator of satellite cell survival as satellite cells activate and establish a TDP-43 requirement for maintaining and repairing skeletal muscle.

ID: 42239172
Title: The retroelement-derived human protein PEG10 is a regulator of mRNA splicing in neurons.
Abstract: Retroelements, including retrotransposons, endogenous retroviruses, and their fragments, as well as rare co-opted or domesticated retroelements, can contribute to neurodegenerative disorders and aging through modulation of gene expression and induction of neuroinflammation. Paternally Expressed Gene 10 (PEG10) is a retroelement-derived human gene that has recently been identified as a putative driver of Amyotrophic Lateral Sclerosis (ALS) and Angelman's Syndrome. PEG10 has been reported to bind nucleic acid and undergoes a complex self-processing pathway that results in gene expression changes when the protein accumulates in cells. Here, we report that PEG10 has selectivity for binding U/G-rich RNAs and influences widespread gene expression changes. PEG10 overexpression mimics the loss of TDP-43 in broad changes to gene expression, including dysregulation of mRNA splicing pathways. Specific changes to mRNA splicing were largely unique between TDP-43 knockdown and PEG10 overexpression, as classic TDP-43 targets including STMN2 were not altered by PEG10. Instead, we identified a unique role for PEG10 in regulating splicing of neuregulin 3 (NRG3), a ligand for the neuronal receptor ERBB4. In SH-SY5Y cells and in human neurons overexpressing PEG10, NRG3 protein levels were decreased along cellular processes, suggesting that these cells are less competent at signaling through the NRG3/ERBB4 axis. Using human patient data, we observed similar changes to NRG3 splicing in UBQLN2-mediated ALS, where PEG10 is accumulated, as well as in some cases of sporadic ALS. In conclusion, the retroelement-derived gene PEG10 plays an unexpected role in regulating splicing of neuronal transcripts, which mimics some of the transcript changes observed in human ALS patient samples. Ultimately, this work has implications for the study of PEG10, and mRNA splicing in neurological diseases associated with elevated PEG10 abundance.

ID: 42244572
Title: Long-read transcriptomics of purified human cortical cell types exposes glial isoform complexity and disease-relevant transcript architecture.
Abstract: Alternative splicing generates extraordinary transcriptomic complexity in the human brain, yet the full-length isoform landscape across human cortical cell types remains uncharted. Combining fluorescence-activated nuclei sorting with long- and short-read RNA sequencing, we generated isoform-resolved transcriptomes for five major lineages of the adult human prefrontal and orbitofrontal cortex: GABAergic neurons, glutamatergic neurons, oligodendrocytes, astrocytes, and microglia. We cataloged over 220,000 full-length isoforms, ~35-56% previously unannotated; novel transcripts were longer, more exon-rich, and predominantly protein-coding. Contrary to the neuron-centric view of cortical complexity, glial lineages, particularly oligodendrocytes and microglia, emerged as the most isoform-diverse populations in the cortex. Differential transcript usage and dominant isoform switching defined cell identity, with ~59-62% of differentially regulated transcripts absent from current annotations. Critically, pathogenic variants were enriched >2-fold at novel splice boundaries within disease genes including POGZ, TARDBP, and PLP1, establishing isoform selection as a primary axis of cortical identity and exposing a layer of pathogenic variation invisible to canonical gene annotations.

ID: 42263412
Title: Beyond the gene: isoform diversity as a key contributor to human brain disorders.
Abstract: The human brain exhibits exceptional transcriptomic complexity, with alternative splicing, promoter usage, and polyadenylation generating extensive transcript-isoform diversity. Isoform dysregulation is increasingly implicated in neurodevelopmental and psychiatric disorders (NPDs), yet the landscape, function, and genetic regulation of brain isoforms remain poorly understood due to limitations of short-read RNA sequencing. Advances in long-read sequencing (LR-seq) enable scalable full-length transcriptome profiling with single-cell and spatial resolution across developmental stages. Here, we review recent progress in isoform discovery, quantification, functional annotation, and genetic regulation, highlighting emerging links to human neurodevelopment and disease. LR-seq studies have uncovered tens of thousands of previously unannotated brain isoforms, with neuronal maturation characterized by increased exon inclusion and progressive 3' untranslated region (3' UTR) lengthening. Isoform-resolved genetic mapping outperforms gene-level analyses for NPD gene discovery and mechanistic interpretation. We argue that a shift from gene-centric to isoform-centric frameworks is essential to fully capture regulatory complexity in human neurogenetics. Together, these advances establish isoform diversity as a fundamental yet underappreciated axis of brain gene regulation and a key entry point for dissecting NPD biology.

ID: 42316301
Title: Intrathecal (G4C2)149 delivery in C9orf72-deficient mice yields mild motor dysfunction and ALS/FTD pathological hallmarks.
Abstract: A repeat expansion in C9ORF72 is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), yet existing mouse models incompletely engage spinal regions implicated in disease. Here, an adeno-associated virus encoding (G4C2)149 repeats was delivered via neonatal intrathecal injection, achieving widespread CNS expression with robust spinal cord targeting. This approach was applied to mice with graded loss of endogenous C9orf72 to interrogate both gain- and loss-of-function mechanisms. Longitudinal motor, behavioral, and pathological analyses revealed that repeat expression primarily drives mild, progressive muscle weakness, whereas coordination deficits were largely genotype dependent. Subtle gait abnormalities and hyperactivity were also observed. Within spinal motor regions, repeat-expressing mice exhibited dipeptide repeat protein accumulation, reduced NeuN-positive area, fewer motor neurons, glial activation, sparse phosphorylated TDP-43 pathology, and increased cryptic TDP-43 splicing. Cross-domain correlations further linked repeat expression, spinal pathology, and motor dysfunction. Collectively, these findings establish that CNS-wide repeat expression combined with reduced C9orf72 produces a coherent, mild ALS/FTD model.

ID: 42327368
Title: Transcriptomic and pathological analysis of the hnRNP network reveals glial involvement in frontotemporal lobar degeneration pathological subtypes.
Abstract: Frontotemporal dementia is a neurodegenerative disorder with a strong heritable component. Frontotemporal lobar degeneration refers to the pathological changes seen in frontotemporal dementia, characterized by atrophy of the frontal and temporal lobes and the presence of abnormal protein inclusions. In the case of frontotemporal lobar degeneration with hyperphosphorylated TDP-43 positive inclusions (FTLD-TDP), five pathological subtypes (A, B, C, D and E) are observed based on the types and distribution of inclusions found in the brain. In all subtypes, there tends to be a large variability in the number of pathological inclusions observed between cases, with limited correlation to clinical manifestations. TDP-43 is an RNA-binding protein belonging to the heterogeneous nuclear ribonucleoprotein (hnRNP) family, which along with other hnRNPs, modulates multiple aspects of RNA processing. HnRNPs other than TDP-43 have been implicated in several neurological diseases, including Amyotrophic Lateral Sclerosis, FTLD-TDP, frontotemporal lobar degeneration with fused in sarcoma (FTLD-FUS) and Alzheimer's disease. Multiple hnRNPs have been found in pathological inclusions in specific subtypes of FTLD-TDP, suggesting potential roles in the disease process. The role of the hnRNP network in frontotemporal lobar degeneration disease pathogenesis, however, has not yet been investigated. This study aimed to comprehensively evaluate the presence and expression of hnRNP proteins in two pathological subtypes of sporadic FTLD-TDP (A and C) as well as the genetic form FTLD-TDP A C9orf72 using immunohistochemistry and gene expression analysis by single-nuclei RNA-sequencing. We found that there was great variability in the frequency of TDP-43 pathology across and within FTLD-TDP pathological subtypes. Our findings suggest that distinct global transcriptomic profiles may underlie the different pathological subtypes of FTLD-TDP. The most prominent transcriptomic changes were observed in oligodendrocytes and astrocytes, involving multiple hnRNPs across frontotemporal lobar degeneration subtypes compared to controls. Transcriptomic co-expression analysis further revealed that glial clusters were more strongly associated with RNA-processing dysfunction and contributed to disease classification. Together, these findings highlight the involvement of the hnRNP network and glial-specific RNA-processing alterations in FTLD-TDP pathophysiology, offering new insight into the molecular distinctions between pathological subtypes and potential targets for future investigation.

ID: 42343570
Title: STMN2 protein depletion via translation deficits and stress granules in amyotrophic lateral sclerosis.
Abstract: STMN2 is an abundant neurospecific protein dysregulated in neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS). We previously reported that cellular stress can lead to STMN2 loss due to TDP-43 nuclear condensation. Here, using human and murine neuronal cell models, multiple pharmacological tools, in situ single-molecule analysis of translation and RNA localisation, and longitudinal analysis of neuronal fitness/survival, we establish TDP-43-independent mechanisms of STMN2 depletion under stress. We find that human STMN2 protein level is extremely labile under acute high-magnitude stress. Early in stress, STMN2 is suppressed via activated proteasomal degradation, phosphorylation and translation repression by stress granules, independently of TDP-43 loss of function in splicing. We further show that STMN2 protein level is highly sensitive to chronic translation deficits, such as those elicited by prolonged low-grade stress. We find that low pre-stress STMN2 sensitises neuronal cells to stress-induced apoptosis, whereas moderately increased STMN2 is protective under stress. Finally, we demonstrate that STMN2 mRNA is upregulated in non-TDP ALS (ALS-FUS) models, which may compensate for translation/stress granule defects in this disease subtype. Consistent with the compensation hypothesis, STMN2 mRNA is also upregulated in the relatively spared (cortex), but not severely affected (spinal cord), CNS regions in ALS-TDP. In conclusion, our study implicates two common denominators in neurodegeneration - dysregulation of translation and stress granules - in STMN2 depletion, independent of TDP-43 loss of function. It also describes an RNA-based compensatory mechanism in ALS underling the unique vulnerability of neurons with developing TDP-43 pathology.

ID: 42347120
Title: RNA-Binding Proteins in Ageing and Age-Related Disease.
Abstract: RNA-binding proteins (RBPs) are essential regulators of all aspects of RNA metabolism, including splicing, stability, localisation, translation, and degradation. Through their ability to recognise specific cis-elements in target transcripts, often via RNA-recognition motifs or other conserved domains, RBPs enable rapid cellular adaptation to stress and maintain proteostasis, particularly in post-mitotic tissues with limited transcriptional flexibility. Accumulating evidence positions RBPs as both modulators and drivers of the molecular hallmarks of ageing, including genomic instability, loss of proteostasis, mitochondrial dysfunction, cellular senescence, and chronic inflammation. This review synthesises peer-reviewed studies on the multifaceted roles of RNA-binding proteins in organismal ageing and age-related diseases. Key themes include the tissue- and age-dependent changes in expression of turnover and translation regulatory RBPs such as HuR (ELAVL1), AUF1 (HNRNPD), TIA-1, and tristetraprolin (ZFP36), which alter the stability of mRNAs encoding cell-cycle regulators, pro-inflammatory cytokines, and stress-response proteins. Systematic downregulation of core splicing factors, including PTBP1 and several heterogeneous nuclear ribonucleoproteins, drives widespread senescence-associated splicing alterations in pathways governing cell division, autophagy, DNA repair, and mitochondrial function, suggesting a causal contribution to the senescent phenotype. Prion-like RBPs such as TDP-43 and FUS exhibit age-dependent mislocalisation, nuclear depletion, and cytoplasmic aggregation, contributing to splicing defects, impaired RNA transport, and neurodegeneration in amyotrophic lateral sclerosis, frontotemporal dementia, and limbic-predominant age-related TDP-43 encephalopathy. Interactions between RBPs and non-coding RNAs, together with disrupted liquid-liquid phase separation dynamics, further exacerbate age-related decline. By integrating mechanistic studies from cellular and animal models with observations in human cohorts, this review underscores RBPs as central nodes linking multiple ageing hallmarks and highlights their potential as biomarkers and therapeutic targets to promote healthy ageing. Limitations of current models and priorities for future translational research are discussed.

ID: 42461232
Title: Deep intronic ANK1 variants causing pseudo-exon inclusion in hereditary spherocytosis: Whole-genome sequencing and functional assessment.
Abstract: 

ID: 42533140
Title: Exchange dynamics and kinetic control of gene regulation complexes.
Abstract: The classical view of gene regulation complexes as stable, modular machines needs amending based on emerging insights into their dynamic nature. Whereas recent advances in structural biology have provided high-resolution snapshots of these complex machines, single-molecule and live-cell imaging techniques reveal a more fluid picture: biological function emerges not from static architectures but from transient, dynamic assemblies that continually exchange their components and whose activity is tuned through kinetic control. In this Perspective, we propose dynamic, reversible assembly as a framework for understanding the mechanisms of RNA processing and gene regulation. Drawing on specific case studies from ribosome biogenesis, spliceosomes, small RNAs and transcription factors, we explore how ribonucleoprotein complexes and transcriptional ensembles form and dissolve in time, how protein intrinsically disordered regions collectively enable transcription factors to achieve specificity, and the kinetic principles underlying the fidelity, adaptability and robustness of cellular processes and their related pathologies. In doing so, we show how molecular interactions are governed by rates rather than by equilibrium affinities, providing a foundation for time-integrated structure-function studies.