Biology subjects

Haag, C.

Publications and source records attributed to Haag, C..

4 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↗

bioRxiv2025

One-step induction of human GABAergic neurons promotes presynaptic development & synapse maturation

Human induced pluripotent stem cells (iPSCs) present a powerful approach to study human brain physiology and disease, yet robust, pure GABAergic induction has remained difficult. Here we present improved, single-step, transposon-based GABAergic induction with Ascl1/Dlx2, which yields, unlike lentiviral approaches, exclusively GABAergic neurons and was validated across three independent iPSC lines. Co-seeding with Ngn2-induced excitatory neurons created stable networks of predefined excitation/inhibition ratios, with corresponding synapse ratios. Proteomic and electrophysiological characterization at different developmental time points showed that the single-step induced GABAergic neurons gain a proteomic profile that maps to different cortical interneuron subtypes and display typical GABAergic synaptic properties, producing large, synchronous and picrotoxin-sensitive currents. During early development, synaptic strength increased threefold, which was accompanied by an increase in expression of proteins exclusively enriched for presynaptic SYNGO terms. Synaptic strength continued to increase during late development but with only minor proteomic changes. Taken together, transposon-based GABAergic induction yields exclusively mature GABAergic neurons suitable for studying genes involved in synaptic maturation and to build excitation/inhibition networks for disease modelling.

neuroscience↗

bioRxiv2018

The key protein of endosomal mRNP transport binds translational landmark sites of cargo mRNAs

RNA-binding proteins (RBPs) determine spatiotemporal gene expression by mediating active transport and local translation of cargo mRNAs. Here, we cast a transcriptome-wide view on the transported mRNAs and cognate RBP binding sites during endosomal messenger ribonucleoprotein (mRNP) transport in Ustilago maydis. Using individual-nucleotide resolution UV crosslinking and immunoprecipitation (iCLIP), we compare the key transport RBP Rrm4 and the newly identified endosomal mRNP component Grp1 that is crucial to coordinate hyphal growth. Both RBPs bind predominantly in the 3 untranslated region of thousands of shared cargo mRNAs, often in close proximity. Intriguingly, Rrm4 precisely binds at stop codons, which constitute landmark sites of translation, suggesting an intimate connection of mRNA transport and translation. Towards uncovering the code of recognition, we identify UAUG as specific binding motif of Rrm4 that is bound by its third RRM domain. Altogether, we provide first insights into the positional organisation of co-localising RBPs on individual cargo mRNAs.

cell biology↗

bioRxiv2017

Parasite-Driven Replacement Of A Sexual By A Closely Related Asexual Taxon In Nature

Asexual species are thought to suffer more from coevolving parasites than related sexuals. Yet, this prediction may be modulated by the fact that closely related sexuals and asexuals often differ in respects other than reproductive mode. Here, we follow the frequency dynamics of sexual and asexual Daphnia pulex in a natural pond that was initially dominated by sexuals. However, coinciding with an epidemic of a microsporidian parasite infecting both sexuals and asexuals, the pond was rapidly taken over by the initially rare asexuals. We experimentally confirm that asexuals are less susceptible and also suffer less from the parasite once infected. These results show the ecological replacement of a sexual taxon by a closely related asexual taxon, as driven by parasites. We suggest that this replacement is, however, not directly connected with the reproductive mode, but rather due to the recent introduction and invasive nature of the asexuals studied.

evolutionary biology↗