Depdc5 regulate the stabilization of GABAergic synapses in a zebrafish model

Introduction: Epilepsies affects over 70 million people worldwide. 30% patients fail to respond
to available anti-epileptic drugs. Such cases bring an urgent need to understand all possible
functions of epilepsy-associated genes so that novel therapeutics can be developed for
patients. 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 domain
related to its mTOR function. However, other mutations are located in domains of unknown
functions, which are highly conserved in vertebrates and do not regulate mTOR signaling. Our
lab previously found decrease in number of GABAergic synapses in 6 dpf (days post
fertilization) zebrafish mutants, thereby, established novel functions of depdc5 in the
development 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 cellular
basis of these non-classical functions of DEPDC5 in brain development.
Methods: I use immunohistochemistry, confocal imaging, and data analysis by Imaris for
studying 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 establishment
of GABAergic synapses, rather for their survival and maintenance. An increase in GABAergic
synapses at 5 days, while a decrease at 6 days, indicate towards a transient excess followed by
failed stabilization and net inhibitory loss during circuit maturation. Currently, we are checking if
the increase at 5dpf is also mTOR independent or not and planning for single-cell RNA
sequencing at 5 and 6dpf.
Conclusion: Altogether, our study will enhance understanding about the mTOR independent
functions of DEPDC5 and ultimately pave the way for identification of new targets and novel
therapeutics for epilepsy patients.