Biology subjects

Zarnescu, D. C.

Publications and source records attributed to Zarnescu, D. C..

3 recordsLinked to original sources

bioRxiv2026

C9orf72-associated G4C2 hexanucleotide repeat expression in Drosophila mushroom bodies causes age dependent TDP-43 pathology and dementia relevant phenotypes mediated in part by the glypican Dlp/GPC6

Hexanucleotide repeat expansions (HREs) in C9orf72 are the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), yet the age-, sex-, repeat-length-, and circuit-specific influence on the pathology of neurons remains incompletely understood. Here, we established a Drosophila model of C9orf72-associated dementia by expressing G4C2 repeats in mushroom body neurons (MBNs), a brain region critical for memory, locomotion, and sleep. Expression of 44X G4C2 repeats ((G4C2)44X) led to progressive axonal thinning, age-dependent accumulation of Repeat Associated Non-AUG (RAN) translated GR-GFP dipeptide repeat (DPR) puncta, premature nuclear-to-cytoplasmic mislocalization of endogenous TDP-43, increased caspase, reduced lifespan and a loss of presynaptic active zones. Behaviorally, (G4C2)44X expression caused locomotor hyperactivity, altered spatial working memory, and fragmentation of sleep architecture in an age- and sex-dependent manner, recapitulating core features of FTD. Surprisingly, the shorter (G4C2)12X repeat, traditionally considered a control, also produced detectable RAN translation and intermediate phenotypes in aging MBNs, suggesting that length- and tissue-associated factors modulate repeat toxicity. We further identified a repeat-length- and age-dependent reduction of the glypican Dally-like protein (Dlp) in (G4C2)44X consistent with disrupted Wnt-related signaling linked to TDP-43 proteinopathies. Restoring Dlp expression in MBNs mitigated locomotor and working-memory alterations, and loss of presynaptic active zones. In contrast, axonal degeneration, TDP-43 mislocalization, and lifespan were not significantly improved by restoring Dlp, suggesting that multiple mechanisms contribute to G4C2-induced toxicity. Supporting our findings in Drosophila MBNs, a CRISPRi screen in TDP-43 knock-down iNeurons identified GPC6, a human ortholog of Dlp, as a significant contributor to TDP-43 dependent synaptic loss. Together, our findings reveal an aging-sensitive, circuit-specific model of C9orf72-associated neurodegeneration and highlight roles for DPR accumulation and Dlp/GPC6 dependent synaptic loss in FTD pathomechanisms.

neuroscience↗

bioRxiv2022

Modelling dementia in Drosophila uncovers shared and specific targets of TDP-43 proteinopathy across ALS and FTD relevant circuits

Amyotrophic lateral sclerosis (ALS) and fronto-temporal dementia (FTD) comprise a spectrum of neurodegenerative diseases linked to TDP-43 proteinopathy, which at the cellular level, is characterized by loss of nuclear TDP-43 and accumulation of cytoplasmic TDP-43 puncta that ultimately cause RNA processing defects including dysregulation of splicing, mRNA transport and translation. Complementing our previous models of ALS, here we report a novel model of FTD based on overexpression of TDP-43 in the Drosophila mushroom body (MB) circuit. This model recapitulates several aspects of FTD pathology including age-dependent neuronal loss, and nuclear depletion and cytoplasmic accumulation of TDP-43, accompanied by behavioral deficits in working memory and sleep that occur before axonal degeneration ensues. RNA immunoprecipitations identify several candidate mRNA targets of TDP-43 in MBs, some of which are unique to the MB circuit while others are shared with motor neurons. Among the latter is the glypican Dally-like-protein (Dlp), a modulator of Wg/Wnt signaling. Using genetic interactions we show that overexpression of Dlp in MBs mitigates TDP-43 dependent working memory deficits. These results highlight the utility of modelling TDP-43 proteinopathy in Drosophila and provide a novel platform for studying the molecular mechanisms underlying FTD, and potentially uncovering shared and circuit specific vulnerabilities in ALS/FTD.

neuroscience↗

bioRxiv2020

TDP-43 proteinopathy alters the ribosome association of multiple mRNAs including the glypican Dally-like protein (Dlp)/GPC6

Amyotrophic lateral sclerosis (ALS) is a genetically heterogeneous neurodegenerative disease in which 97% of patients exhibit cytoplasmic aggregates containing the RNA binding protein TDP-43. Using tagged ribosome affinity purifications in Drosophila models of TDP-43 proteinopathy, we identified TDP-43 dependent translational alterations in motor neurons impacting the spliceosome, pentose phosphate and oxidative phosphorylation pathways. A subset of the mRNAs with altered ribosome association are also enriched in TDP-43 complexes suggesting that they may be direct targets. Among these, dlp mRNA, which encodes the glypican Dally like protein (Dlp)/GPC6, a wingless (Wg/Wnt) signaling regulator is insolubilized both in flies and patient tissues with TDP-43 pathology. While Dlp/GPC6 forms puncta in the Drosophila neuropil and ALS spinal cords, it is reduced at the neuromuscular synapse in flies suggesting compartment specific effects of TDP-43 proteinopathy. These findings together with genetic interaction data show that Dlp/GPC6 is a novel, physiologically relevant target of TDP-43 proteinopathy.

neuroscience↗