Environmental and molecular modulation of motor individuality in larval zebrafish

Abstract

Innate behavioral biases such as human handedness are a ubiquitous form of inter-individual variation that are not strictly hardwired into the genome and are influenced by diverse internal and external cues. Yet, genetic and environmental factors modulating behavioral variation remain poorly understood, especially in vertebrates. To identify genetic and environmental factors that influence behavioral variation, we take advantage of larval zebrafish light-search behavior. During light-search, individuals preferentially turn in leftward or rightward loops, in which directional bias is sustained and non-heritable, and maintained by a habenula-rostral PT circuit. Here we use a medium-throughput recording strategy and unbiased analysis to show that significant individual to individual variation exists in wildtype larval zebrafish turning preference. We classify stable left, right, and unbiased turning types, with most individuals exhibiting a directional preference. Raising larvae at elevated temperature selectively reduces the leftward turning type and impacts rostral PT neurons, specifically. Exposure to conspecifics, variable salinity, environmental enrichment, and physical disturbance does not significantly impact inter-individual turning bias. Pharmacological manipulation of Notch signaling and carrying a mutant allele of a known Notch pathway affecter gene, gsx2, disrupted turn bias individuality in a dose-dependent manner. These results establish that larval zebrafish is a powerful vertebrate model for inter-individual variation with sensitivity to specific environmental perturbations and gene dosage.

Thalamic regulation of a visual critical period and motor behavior

“…Recently, we published a screen of etiologically relevant environmental factors showing that turn bias direction can be modulated by environmental experience. However, we did not elucidate a causative factor imposing left or right turn bias during search behavior 27 . Here we show that asymmetric visual experience instructs this outcome.…”

“…This stereotactic behavior is consistent with search behavior patterns observed across numerous species 28–30 . In wildtype zebrafish, left and right turning types are observed in equal proportions 26,27 . Moreover, turn direction preference is also not heritable, implying stochastic molecular or environmental cues determine an individual’s turning type 26,27 .…”

“…In wildtype zebrafish, left and right turning types are observed in equal proportions 26,27 . Moreover, turn direction preference is also not heritable, implying stochastic molecular or environmental cues determine an individual’s turning type 26,27 . However, we previously were unable to identify a developmental ‘switch’ instructing an individual to adopt a left or right turn bias preference.…”

“…We injected y279 larvae with a UAS:chEF-v2a-mCherry driver for optical stimulation 63 , UAS:TagRFP-v2a-paGFP (used only for TagRFP expression) as a control, or UAS:GtACR2-tdTomato for optical inhibition 64 . Because the y279 line labels neurons in addition to AMNs 26,27 (see Supplementary…”

“…At 3dpf, Tg(y279:Gal4; UAS:Kaede) larvae were fixed overnight at 4°C in 4% paraformaldehyde in 1x PBS and 0.1% Tween20. After fixation, embryos were washed in 1x PBS with 0.1% Tween 20, and labeling was conducted using HCR RNA-Fish protocol (Hageter et al 2021). Imaging was performed on an Olympus Fluoview FV1000 confocal using a 40x oil immersion objective.…”