Biology subjects

Brais, B.

Publications and source records attributed to Brais, B..

5 recordsLinked to original sources

bioRxiv2025

SynTEF1 restores the functional disease phenotype of SCA27B in an hiPSC-derived neuronal disease model

Spinocerebellar Ataxia 27B (SCA27B), caused by a deep-intronic GAA repeat expansion in the first intron of the FGF14 gene, is one of the most frequent genetic ataxias. Its underlying disease mechanisms remain largely unknown, and disease-modifying therapies targeting upstream processes are lacking. Here we hypothesized that (i) SCA27B is driven by transcriptional repression of FGF14, which encodes a protein regulating ion channels at the axon initial segment (AIS), resulting in reduced Na+ channel availability and neuronal excitability, and that (ii) these defects can be restored by a synthetic elongation transcription factor (Syn-TEF1). We assessed FGF14 mRNA levels by qPCR and neuronal function by whole-cell patch-clamp recordings in iPSC-derived neurons from two SCA27B patients and two healthy controls. Patients carried GAA repeat expansions that were either monoallelic (391/16 repeats) or biallelic (315/290 repeats), exceeding the common pathogenicity threshold of >250 repeats. FGF14 mRNA levels were reduced approximately to 60% and 70% of control levels in monoallelic and biallelic SCA27B neurons, respectively. This was accompanied by impaired excitability, with cumulative action potential (AP) firing reduced to 38% and 45% of control levels in monoallelic and biallelic lines, respectively, and peak Na current density reduced to 46% and 41%, while voltage-dependent gating of Na channels remained unchanged. Treatment with Syn-TEF1 significantly increased FGF14 mRNA expression and restored cumulative AP firing to 83% and 135% of control levels in monoallelic and biallelic neurons, respectively, and Na peak current density to 95% and 138%. These findings strongly suggest that the pathophysiological cascade in SCA27B - from FGF14 repression to impaired Na+ currents and decreased neuronal excitability - can be reversed by an elongation transcription factor. Our results thus provide a rationale for further exploring Syn-TEF1 as a first gene-targeted, disease-modifying therapeutic approach for SCA27B.

neuroscience↗

bioRxiv2023

Loss of zebrafish dcst2 expression is not associated with muscle abnormalities

In this study we examined if the gene encoding Dendritic Cell-specific Six Transmembrane domain containing protein 2 (dcst2) plays a role in vertebrate muscle biology. Using the CRISPR/Cas9 mutagenic system we generated a 2 nucleotide deletion in exon 3 of the zebrafish ortholog dcst2 which resulted in a premature stop codon. Homozygous carriers of the mutation displayed reduced transcriptional expression of dcst2 suggesting that our mutation was indeed disrupting gene function. Mutant dcst2 zebrafish developed normally to adulthood and displayed no differences in motor function using a free-swim and swim tunnel assays. Furthermore, histological examination of muscle cells revealed no differences in slow-twitch or fast-twitch muscle cell cross-sectional area in our mutants. We did observe that dcst2-/- zebrafish were slightly heavier in weight and males were infertile. The data collected here, suggest that dcst2 does not play a role in zebrafish muscle cell biology.

molecular biology↗

bioRxiv2023

A common flanking variant is associated with enhanced meiotic stability of the FGF14-SCA27B locus

The factors driving initiation of pathological expansion of tandem repeats remain largely unknown. Here, we assessed the FGF14-SCA27B (GAA)*(TTC) repeat locus in 2,530 individuals by long-read and Sanger sequencing and identified a 5-flanking 17-bp deletion-insertion in 70.34% of alleles (3,463/4,923). This common sequence variation was present nearly exclusively on alleles with fewer than 30 GAA-pure repeats and was associated with enhanced meiotic stability of the repeat locus.

genetics↗

bioRxiv2021

The J domain of sacsin disrupts intermediate filament assembly

Autosomal Recessive Spastic Ataxia of the Charlevoix Saguenay (ARSACS), is caused by loss of function mutations in the SACS gene, which encodes sacsin, a giant protein of 520 kDa. A key feature of the absence of sacsin in cells is the formation of abnormal bundles of intermediate filaments (IF) including neurofilaments (NF) in neurons and vimentin IF in fibroblasts, suggesting a role of sacsin in IF homeostasis. Sacsin contains a J domain (SacsJ) homologous to Hsp40, that can interact with Hsp70 chaperones. The SacsJ domain resolved NF bundles in cultured Sacs-/- neurons, however, its mechanism is still unclear. Here, we focused on the role of SacsJ in NF assembly. We report that the SacsJ domain directly interacts with NF proteins in vitro to disassemble NFL filaments, and to inhibit their initial assembly, in the absence of Hsp70. We generated a cell-penetrating peptide derived from this domain, SacsJ-myc-TAT, which was efficient in disassembling both vimentin IF and NF in cultured fibroblasts and Sacs+/+ motor neurons as well as NF bundles in cultured Sacs-/- motor neurons. Whereas a normal NF network was restored in Sacs-/- neurons treated with the SacsJ peptide, there was some loss of IF networks in Sacs+/+ fibroblasts or neurons. These results suggest that SacsJ is a key regulator of NF and IF networks in cells, with implications for its therapeutic use.

cell biology↗

bioRxiv2019

Investigation of the pathogenic RFC1 repeat expansion in a Canadian and a Brazilian ataxia cohort: identification of novel conformations

A homozygous pentanucleotide expansion in the RFC1 gene has been shown to be a common cause of late-onset ataxia. In the general population a total of four different repeat conformations have been observed: a wild type sequence AAAAG (11 repeats), and longer expansions of AAAAG, AAAGG and AAGGG sequences. However, in ataxia cases only the AAGGG expansion has been shown to be pathogenic. In this study, we assessed the prevalence and nature of RFC1 repeat expansions in three adult-onset ataxia cohorts: Brazilian (n = 23) and Canadian (n = 26) cases that tested negative for other known ataxia mutations, as well as a cohort of randomly selected Canadian cases (n = 128) without regard to a genetic diagnosis. We identified the homozygous AAGGG pathogenic expansion in only one Brazilian family with two affected siblings, and in one Canadian case. The RFC1 expansion may therefore not be a common cause of adult-onset ataxia in these populations. Interestingly we observed two new repeat motifs, AAGAG and AGAGG, which indicates the dynamic nature of the pentanucleotide expansion sequence. To assess the frequency of these two new repeat conformations in the general population we screened 163 healthy individuals. These novel motifs were more frequent in patients versus controls. While we cannot be certain that the homozygous genotypes of the novel expanded conformations are pathogenic, their occurrence should nonetheless be taken into consideration in future studies.

genetics↗