Biology subjects

Sumathipala, S. H.

Publications and source records attributed to Sumathipala, S. H..

3 recordsLinked to original sources

bioRxiv2025

Cyfip2 mediates sensorimotor integration of visual input through Rac1-dependent actin remodeling

Sensorimotor integration of visual input is essential for adaptive behaviors such as navigation, hunting, and escape from danger, yet our understanding of the developmental mechanisms that assemble these visuomotor circuits remains incomplete. Cytoplasmic FMRP-interacting protein 2 (cyfip2) is a key factor in retinotectal axon guidance in zebrafish larvae, and it has conserved roles in regulating actin dynamics and mRNA translation. Variants in human CYFIP2 cause neurodevelopmental disabilities including vision deficits, but how it functions to shape visually-driven behavior is unclear. Here we measured multiple visually-mediated behaviors, brain-wide activity, and conditional rescue of behavioral defects in larval zebrafish to define cyfip2s roles in assembling visual sensorimotor circuits. cyfip2 mutants display severe deficits in prey capture and dark and light flash responses, despite normal optokinetic responses, indicating intact retinal phototransduction but disrupted downstream sensorimotor integration. Both spontaneous and stimulus-evoked neuronal activity are reduced in the optic tectum of cyfip2 mutants, as measured by phospho-ERK immunostaining and pan-neuronal calcium, consistent with impaired functional input from retinal ganglion cells. Finally, using conditional transgenic alleles to temporally control Cyfip2 expression, we identified a critical window from 30-50 hours post-fertilization during which Cyfip2 acts through Rac1-dependent actin polymerization but not FMRP-mediated translation to establish visual behavior circuits. Together, these findings define how and when Cyfip2 acts as a critical organizer of vertebrate visual circuit development, providing mechanistic insight into the visual and motor deficits in human subjects with variants in CYFIP2.

neuroscience↗

bioRxiv2023

Cyfip2 controls the acoustic startle threshold through FMRP, actin polymerization, and GABAB receptor function.

Animals process a constant stream of sensory input, and to survive they must detect and respond to dangerous stimuli while ignoring innocuous or irrelevant ones. Behavioral responses are elicited when certain properties of a stimulus such as its intensity or size reach a critical value, and such behavioral thresholds can be a simple and effective mechanism to filter sensory information. For example, the acoustic startle response is a conserved and stereotyped defensive behavior induced by sudden loud sounds, but dysregulation of the threshold to initiate this behavior can result in startle hypersensitivity that is associated with sensory processing disorders including schizophrenia and autism. Through a previous forward genetic screen for regulators of the startle threshold a nonsense mutation in Cytoplasmic Fragile X Messenger Ribonucleoprotein (FMRP)-interacting protein 2 (cyfip2) was found that causes startle hypersensitivity in zebrafish larvae, but the molecular mechanisms by which Cyfip2 establishes the acoustic startle threshold are unknown. Here we used conditional transgenic rescue and CRISPR/Cas9 to determine that Cyfip2 acts though both Rac1 and FMRP pathways, but not the closely related FXR1 or FXR2, to establish the acoustic startle threshold during early neurodevelopment. To identify proteins and pathways that may be downstream effectors of Rac1 and FMRP, we performed a candidate-based drug screen that indicated that Cyfip2 can also act acutely to maintain the startle threshold branched actin polymerization and N-methyl D-aspartate receptors (NMDARs). To complement this approach, we used unbiased discovery proteomics to determine that loss of Cyfip2 alters cytoskeletal and extracellular matrix components while also disrupting oxidative phosphorylation and GABA receptor signaling. Finally, we functionally validated our proteomics findings by showing that activating GABAB receptors, which like NMDARs are also FMRP targets, restores normal startle sensitivity in cyfip2 mutants. Together, these data reveal multiple mechanisms by which Cyfip2 regulates excitatory/inhibitory balance in the startle circuit to control the processing of acoustic information.

neuroscience↗

bioRxiv2023

Context-dependent hyperactivity in syngap1a and syngap1b zebrafish autism models.

Background and AimsSYNGAP1 disorder is a prevalent genetic form of Autism Spectrum Disorder and Intellectual Disability (ASD/ID) and is caused by de novo or inherited mutations in one copy of the SYNGAP1 gene. In addition to ASD/ID, SYNGAP1 disorder is associated with comorbid symptoms including treatment-resistant-epilepsy, sleep disturbances, and gastrointestinal distress. Mechanistic links between these diverse symptoms and SYNGAP1 variants remain obscure, therefore, our goal was to generate a zebrafish model in which this range of symptoms can be studied. MethodsWe used CRISPR/Cas9 to introduce frameshift mutations in the syngap1a and syngap1b zebrafish duplicates (syngap1ab) and validated these stable models for Syngap1 loss-of-function. Because SYNGAP1 is extensively spliced, we mapped splice variants to the two zebrafish syngap1a and b genes and identified mammalian-like isoforms. We then quantified locomotory behaviors in zebrafish syngap1ab larvae under three conditions that normally evoke different arousal states in wild type larvae: aversive, high-arousal acoustic, medium-arousal dark, and low-arousal light stimuli. ResultsWe show that CRISPR/Cas9 indels in zebrafish syngap1a and syngap1b produced loss-of-function alleles at RNA and protein levels. Our analyses of zebrafish Syngap1 isoforms showed that, as in mammals, zebrafish Syngap1 N- and C-termini are extensively spliced. We identified a zebrafish syngap1 1-like variant that maps exclusively to the syngap1b gene. Quantifying locomotor behaviors showed that syngap1ab larvae are hyperactive compared to wild type but to differing degrees depending on the stimulus. Hyperactivity was most pronounced in low arousal settings, with overall movement increasing with the number of mutant syngap1 alleles. ConclusionsOur data support mutations in zebrafish syngap1ab as causal for hyperactivity associated with elevated arousal that is especially pronounced in low-arousal environments.

neuroscience↗