Regulation of neuron-specific gene transcription by stress hormone signalling requires synaptic activity in zebrafish

Abstract

28The Glucocorticoid Receptor (GR) co-ordinates metabolic and behavioural 29 responses to stressors. We hypothesised that GR influences behaviour by 30 modulating specific epigenetic and transcriptional processes in the brain. Using the 31 zebrafish as a model organism, the brain methylomes of wild-type and gr s357 mutant 32 adults were analysed and GR-sensitive, differentially methylated regions (GR-DMRs) 33 were identified. Two genes with GR-DMRs exhibited distinct methylation and 34 transcriptional sensitivities to GR: the widely expressed direct GR target fkbp5 and 35 neuron-specific aplp1. In larvae, neural activity is required for GR-mediated 36 transcription of aplp1, but not for that of fkbp5. GR regulates metabotropic glutamate 37 receptor gene expression, the activities of which also modulated aplp1 expression, 38 implicating synaptic neurotransmission as an effector of GR function upstream of 39 aplp1. Our results identify two distinct routes of GR-regulated transcription in the 40 brain, including a pathway through which GR couples endocrine signalling to 41 synaptic activity-regulated transcription by modulating metabotropic glutamate 42 receptor expression. 43 44 45 46 Eachus, Subramanya et al. Results 87A loss-of-function mutation in the nr3c1 gene encoding the zebrafish Glucocorticoid 88Receptor (GR), denoted gr s357 , was previously shown to cause abnormally high 89 levels of HPI axis gene expression, elevated blood cortisol, and behavioural 90 abnormalities suggestive of increased behavioural anxiety (Griffiths et al., 2012; Ziv 91 et al., 2013). An initial analysis of locomotor behaviours and measurement of whole 92 body cortisol of wild-type and gr s357 mutant adults and larvae supported and 93 extended these findings (Figure 1), confirming a requirement for GR in regulation of 94 both nervous and endocrine system functions in larval and adult stages. gr s357 95 mutant larvae and adults swam more slowly, larvae were more dispersed, and adults 96 froze more frequently, were less exploratory and less dark aversive than age-97 matched wild-type animals (Figure 1 A-J). Moreover, gr s357 mutant larvae and adults 98 had higher whole body cortisol levels than age-matched wild-type animals (Figure 1 99