Biology subjects

Fiszer, A.

Publications and source records attributed to Fiszer, A..

4 recordsLinked to original sources

bioRxiv2026

Modeling ATN1 mutations in human iPSCs reveals early developmental roles of atrophin-1

Atrophin-1 (ATN1), encoded by the ATN1 gene, is an evolutionarily conserved transcriptional corepressor implicated in neuronal development and severe incurable disorders, including the polyglutamine (polyQ) disease - dentatorubral-pallidoluysian atrophy (DRPLA), and the neurodevelopmental syndrome CHEDDA. However, the cellular function of ATN1 and its role during early human development remain largely uncharacterized. Here, we generated an isogenic panel of human induced pluripotent stem cell (iPSC) lines, establishing a novel resource for comprehensive studies of ATN1 function and dysfunction. This panel includes a DRPLA patient-derived line (wt/mut), CRISPR-Cas9-corrected wild-type controls (wt/wt), complete ATN1 knock-out clones (-/-), and heterozygous lines expressing either a wild-type or a mutant allele (wt/- and -/mut). While pluripotency markers remained unaffected across all variants, further characterization revealed marked proliferation deficits in ATN1 knock-out lines and heterozygous iPSCs without wild-type allele expression. Moreover, the formation of punctate ATN1 assemblies was enhanced in iPSCs with -/mut variants. The pronounced phenotype observed in cells expressing only the mutant ATN1 allele may result from a combination of loss-of-function and toxic gain-of-function mechanisms. Overall, the generated panel of iPSC lines provides a unique cellular platform for investigating ATN1-dependent molecular mechanisms and their contribution to neuronal development and disease.

cell biology↗

bioRxiv2025

Overview of non-coding RNAs with CAG repeats and the case of mutation-containing circRNA in polyglutamine disease patients

CAG trinucleotide repeats are present in protein-coding and non-coding RNAs (ncRNAs). They are polymorphic in length and can cause neurodegenerative diseases when expanded, e.g., spinocerebellar ataxia type 7 (SCA7) is caused by a mutation in the ATXN7 gene. We focused on RNAs with at least 10 CAG repeats and identified several hundred mRNAs, long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs) originating from 49 genomic loci. These loci differ in the rate of length polymorphism in the population, and some of the tracts show an interesting pattern of adjacent CAA triplet, as well as present variable interruption profiles. For ATXN7 locus, we investigated two circRNAs for which we confirmed the expression in the human brain, SCA7 fibroblasts and blood samples. Moreover, we report an intriguing example of circRNA containing a mutant CAG tract, experimentally validated in SCA7 patients.

molecular biology↗

bioRxiv2024

Huntingtin loss-of-function contributes to transcriptional deregulation in Huntington's disease

Huntingtons disease (HD) is a fatal neurodegenerative disorder that is caused by the expansion of CAG repeats in the HTT gene, which results in a long polyglutamine (polyQ) tract in the huntingtin protein (HTT). In this study, we searched for networks of deregulated RNAs that contribute to initial transcriptional changes in HD neuronal cells and HTT-deficient cells. We used RNA-seq (including small RNA sequencing) to analyze a set of isogenic, human induced pluripotent stem cell (iPSC)-derived neural stem cells (NSCs); and we observed numerous changes in gene expression and substantial dysregulation of miRNA expression in HD and HTT-knockout (HTT-KO) cell lines. The gene set that was upregulated in both HD and HTT-KO cells was enriched in genes that are associated with DNA binding and regulation of transcription. For both of these models, we confirmed the substantial upregulation of the transcription factors (TFs) TWIST1, SIX1, TBX1, TBX15, MSX2, MEOX2 and FOXD1 in NSCs and medium spiny neuron (MSN)-like cells. Moreover, we identified miRNAs that were consistently deregulated in HD and HTT-KO NSCs and MSN-like cells, including miR-214, miR-199, and miR-9. We suggest that these miRNAs function in the network that regulates TWIST1 and HTT expression via regulatory feed-forward loop (FFL) in HD. Additionally, we reported that the expression of selected TFs and miRNAs tended to progressively change during the neural differentiation of HD cells, what was not observed in HTT-KO model. Based on comparing the HD and HTT-KO cell lines, we propose that early transcriptional deregulation in HD is largely caused by loss of HTT function.

neuroscience↗

bioRxiv2020

RAN translation of the expanded CAG repeats in the SCA3 disease context

Spinocerebellar ataxia type 3 (SCA3) is a progressive neurodegenerative disorder caused by a CAG repeat expansion in the ATXN3 gene encoding the ataxin-3 protein. Despite extensive research the exact pathogenic mechanisms of SCA3 are still not understood in depth. In the present study, to gain insight into the toxicity induced by the expanded CAG repeats in SCA3, we comprehensively investigated repeat-associated non-ATG (RAN) translation in various cellular models expressing translated or non-canonically translated ATXN3 sequences with an increasing number of CAG repeats. We demonstrate that two SCA3 RAN proteins, polyglutamine (polyQ) and polyalanine (polyA), are found only in the case of CAG repeats of pathogenic length. Despite having distinct cellular localization, RAN polyQ and RAN polyA proteins are very often coexpressed in the same cell, impairing nuclear integrity and inducing apoptosis. We provide for the first time mechanistic insights into SCA3 RAN translation indicating that ATXN3 sequences surrounding the repeat region have an impact on SCA3 RAN translation initiation and efficiency. We revealed that RAN translation of polyQ proteins starts at non-cognate codons upstream of the CAG repeats, whereas RAN polyA proteins are likely translated within repeats. Furthermore, integrated stress response activation enhances SCA3 RAN translation. We suggest that RAN translation in SCA3 is a common event substantially contributing to SCA3 pathogenesis and that the ATXN3 sequence context plays an important role in triggering this unconventional translation.

molecular biology↗