Depdc5 regulate the stabilization of GABAergic synapses in a zebrafish model

Introduction: Epilepsies affects over 70 million people worldwide. 30% patients fail to respondto available anti-epileptic drugs. Such cases bring an urgent need to understand all possiblefunctions of epilepsy-associated genes so that novel therapeutics can be developed forpatients. Loss of function mutations of DEPDC5 account for 12-37% cases of focal seizures.DEPDC5 inhibits mTOR, and some disease-causing mutations are located within protein domainrelated to its mTOR function. However, other mutations are located in domains of unknownfunctions, which are highly conserved in vertebrates and do not regulate mTOR signaling. Ourlab previously found decrease in number of GABAergic synapses in 6 dpf (days postfertilization) zebrafish mutants, thereby, established novel functions of depdc5 in thedevelopment of inhibitory synapses in brain that are independent of its mTOR functions.Objectives: The objective of my post-doctoral work is to understand the molecular and cellularbasis of these non-classical functions of DEPDC5 in brain development.Methods: I use immunohistochemistry, confocal imaging, and data analysis by Imaris forstudying GABAergic synapse.Results: I found an increase in the number of GABAergic synapses at 5 dpf in depdc5 mutants,while no change at 4dpf. This indicates that depdc5 is not required for the initial establishmentof GABAergic synapses, rather for their survival and maintenance. An increase in GABAergicsynapses at 5 days, while a decrease at 6 days, indicate towards a transient excess followed byfailed stabilization and net inhibitory loss during circuit maturation. Currently, we are checking ifthe increase at 5dpf is also mTOR independent or not and planning for single-cell RNAsequencing at 5 and 6dpf.Conclusion: Altogether, our study will enhance understanding about the mTOR independentfunctions of DEPDC5 and ultimately pave the way for identification of new targets and noveltherapeutics for epilepsy patients.