Using zebrafish to understand the neurodevelopment role of susceptibility genes for autism spectrum disorder

Several studies in the last three years have revealed that members of a synaptic cell adhesion network are candidate susceptibility genes for Autism spectrum disorder (ASD). These genes include neurexin-1 (NRXN1), neuroligin-1 (NLGN1), NLGN4, contactin associated protein 2 (CNTNAP2 or previously known as CASPR2) and Shank3. ASD is increasingly attributed to a disorder of brain function rather than brain anatomy. We have begun to address the role of gene-gene interactions within the synaptic cell adhesion pathway involved in neural circuits associated with simple behaviours using the zebrafish animal model. We are focusing on interactions between identified susceptibility genes NLGN-1, NLGN-4, NRXN-1□, Shank3 and CNTNAP2 as well as on interactions of these genes with other known synaptic cell adhesion pathway genes (LRRTM2, PSD-95 and CASK) in order to begin to understand the function of gene networks underlying the emergence of early behaviours. We have generated morpholinos against NRXN-1a□, NRXN1b□ and CNTNAP2 and injected them individually into one cell embryos and then assessed the touch and escape responses at 30 and 45 h, respectively. Knock down of either NRXN-1a□, NRXN1b□ or CNTAP2 significantly reduced the touch response at 30 hpf to a similar extent. The high penetrance of these phenotypes (71–84%) suggest that these genes are playing a major role in the development of the underlying neural circuitry responsible for this behaviour. In contrast, at 45 hpf knock down of NRXN-1a□ had no effect on the escape response, knock down of NRXN1b□ either extinguished or reduced the response, while knock down of CNTNAP2 produced an abnormal response. These very different phenotypes suggest very different roles of these synaptic adhesion network genes in the underlying neural circuitry. Our analyses are beginning to reveal the most critical genes involved in development of neural circuits underlying a simple behaviour