bioRxiv Subject Collection: Neuroscience's Journal
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Sunday, January 28th, 2024
| Time |
Event |
| 2:45a |
Motor neurons are dispensable for the assembly of a sensorimotor circuit for gaze stabilization
Sensorimotor reflex circuits engage distinct neuronal subtypes, defined by precise connectivity, to transform sensation into compensatory behavior. Whether and how motor neuron populations specify the subtype fate and/or sensory connectivity of their pre-motor partners remains controversial. Here, we discovered that motor neurons are dispensable for proper connectivity in the vestibular reflex circuit that stabilizes gaze. We first measured activity following vestibular sensation in pre-motor projection neurons after constitutive loss of their extraocular motor neuron partners. We observed normal responses and topography indicative of unchanged functional connectivity between sensory neurons and projection neurons. Next, we show that projection neurons remain anatomically and molecularly poised to connect appropriately with their downstream partners. Lastly, we show that the transcriptional signatures that typify projection neurons develop independently of motor partners. Our findings comprehensively overturn a long-standing model: that connectivity in the circuit for gaze stabilization is retrogradely determined by motor partner-derived signals. By defining the contribution of motor neurons to specification of an archetypal sensorimotor circuit, our work speaks to comparable processes in the spinal cord and advances our understanding of general principles of neural development. | | 6:18p |
Dual-targeting CRISPR-CasRx reduces C9orf72 ALS/FTD sense and antisense repeat RNAs in vitro and in vivo
The most common genetic cause of both frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) is a G4C2 repeat expansion in intron 1 of the C9orf72 gene. This repeat expansion undergoes bidirectional transcription to produce sense and antisense repeat RNA species. Both sense and antisense-derived repeat RNAs undergo repeat-associated non-AUG translation in all reading frames to generate five distinct dipeptide repeat proteins (DPRs). Importantly, toxicity has been associated with both sense and antisense repeat-derived RNA and DPRs. This suggests targeting both sense and antisense repeat RNA may provide the most effective therapeutic strategy. The RNA-targeting CRISPR-Cas13 systems offer a promising avenue for simultaneous targeting of multiple RNA transcripts, as they mature their own guide arrays, thus allowing targeting of more than one RNA species from a single construct. We show that CRISPR-Cas13d originating from Ruminococcus flavefaciens (CasRx) can successfully reduce C9orf72 sense and antisense repeat transcripts and DPRs to background levels in HEK cells overexpressing C9orf72 repeats. CRISPR-CasRx also markedly reduced the endogenous sense and antisense repeat RNAs and DPRs in three independent C9orf72 patient-derived iPSC-neuron lines, without detectable off-target effects. To determine whether CRISPR-CasRx is effective in vivo, we treated two distinct C9orf72 repeat mouse models using AAV delivery and observed a significant reduction in both sense and antisense repeat-containing transcripts. Taken together this work highlights the potential for RNA-targeting CRISPR systems as therapeutics for C9orf72 ALS/FTD. |
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