Glycine-alanine dipeptide repeats spread rapidly in a repeat length- and age-dependent manner in the fly brain

Abstract

Hexanucleotide repeat expansions of variable size in C9orf72 are the most prevalent genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia. Sense and antisense transcripts of the expansions are translated by repeat-associated non-AUG translation into five dipeptide repeat proteins (DPRs). Of these, the polyGR, polyPR and, to a lesser extent, polyGA DPRs are neurotoxic, with polyGA the most abundantly detected DPR in patient tissue. Trans-cellular transmission of protein aggregates has recently emerged as a major driver of toxicity in various neurodegenerative diseases. In vitro evidence suggests that the C9 DPRs can spread. However, whether this phenomenon occurs under more complex in vivo conditions remains unexplored. Here, we used the adult fly brain to investigate whether the C9 DPRs can spread in vivo upon expression in a subset of neurons. We found that only polyGA can progressively spread throughout the brain, which accumulates in the shape of aggregate-like puncta inside recipient cells. Interestingly, GA transmission occurred as early as 3 days after expression induction. By comparing the spread of 36, 100 and 200 polyGA repeats, we found that polyGA spread is enhanced upon expression of longer GA DPRs. Transmission of polyGA is greater in older flies, indicating that age-associated factors exacerbate the spread. These data highlight a unique propensity of polyGA to spread throughout the brain, which could contribute to the greater abundance of polyGA in patient tissue. In addition, we present a model of early GA transmission that is suitable for genetic screens to identify mechanisms of spread and its consequences in vivo.

Preferred conformations in the disordered region of human CPEB3, a functional amyloid linked to memory consolidation

“…One of the most striking features in hCPEB3's sequence is a short dipeptide protein motif (Val-Gly)5 spanning residues 271 -281, which is reminiscent of longer (Ala-Gly)N and (Pro-Gly)N and (Arg-Gly)N dipeptide repeat proteins encoded by mutant C9orf72 which have been implicated in ALS (Morón-Oset et al, 2019); (Mizielinska et al, 2014). Our in silico analysis identified this segment as having a high potential to form amyloid (Ramírez de Mingo et al, 2020).…”

Co-expression of C9orf72 related dipeptide-repeats over 1000 repeat units reveals age- and combination-specific phenotypic profiles in Drosophila

“…Current Drosophila models of C9orf72 related DPRs have proven beneficial in dissecting the molecular mechanisms contributing towards neurodegeneration in FTD and MND. However, recent observations that the pathological properties of DPRs alter with length suggests that shorter repeat models may not fully recapitulate disease mechanisms [2,19,31]. Current Drosophila models may, therefore, be limited by their relatively short repeat length, the longest being 100 repeats.…”

Amyotrophic Lateral Sclerosis Genes in Drosophila melanogaster

“…When 36 copies of (GA), (GR), or (PR) were used, no spreading was observed. In contrast, (GA) 100 but not (GR) 100 or (PR) 100 was detected in fly brains after 3 days of expression in ORNs [ 127 ]. Accordingly, only (GA) 100 was detected in axons and synaptic terminals of ORNs.…”