RhoGEF9 splice isoforms influence neuronal maturation and synapse formation downstream of α2 GABAA receptors.

Claire De Groot,Kai Kaila,Cornelia Schwerdel,Shiva K Tyagarajan,Yuan-Chen Tsai,Manuela Kohler,Jean-Marc Fritschy,Georgia Parkin,Simon Früh,Giovanna Bosshard,Amalia Floriou-Servou,Hongyan Wang

doi:10.1371/journal.pgen.1007073

Claire De Groot, Kai Kaila + Show 10 more

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https://doi.org/10.1371/journal.pgen.1007073

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Journal: PLoS Genetics	Publication Date: Oct 25, 2017
Citations: 16	License type: CC BY 4.0

Affiliation: University of Zurich, University of Helsinki

Abstract

In developing brain neuronal migration, dendrite outgrowth and dendritic spine outgrowth are controlled by Cdc42, a small GTPase of the Rho family, and its activators. Cdc42 function in promoting actin polymerization is crucial for glutamatergic synapse regulation. Here, we focus on GABAergic synapse-specific activator of Cdc42, collybistin (CB) and examine functional differences between its splice isoforms CB1 and CB2. We report that CB1 and CB2 differentially regulate GABAergic synapse formation in vitro along proximal-distal axis and adult-born neuron maturation in vivo. The functional specialization between CB1 and CB2 isoforms arises from their differential protein half-life, in turn regulated by ubiquitin conjugation of the unique CB1 C-terminus. We report that CB1 and CB2 negatively regulate Cdc42; however, Cdc42 activation is dependent on CB interaction with gephyrin. During hippocampal adult neurogenesis CB1 regulates neuronal migration, while CB2 is essential for dendrite outgrowth. Finally, using mice lacking Gabra2 subunit, we show that CB1 function is downstream of GABAARs, and we can rescue adult neurogenesis deficit observed in Gabra2 KO. Overall, our results uncover previously unexpected role for CB isoforms downstream of α2-containing GABAARs during neuron maturation in a Cdc42 dependent mechanism.

Highlights

During CNS development, GABAergic transmission regulates key steps of neurogenesis and neuronal circuit formation [1,2]
Using mice lacking Gabra2 subunit, we show that CB1 function is downstream of GABAA receptors (GABAARs), and we can rescue adult neurogenesis deficit observed in Gabra2 KO
Representative images of neurons expressing either eGFP-gephyrin alone, or together with mCherry-CB isoforms opposed to vesicular GABA transporter-positive terminals are shown (Fig 1B–1F)

Summary

Introduction

During CNS development, GABAergic transmission regulates key steps of neurogenesis and neuronal circuit formation [1,2]. In addition to GABAAR and gephyrin, several proteins have been found to be essential for GABAergic synapse structure and function [9]. A major unresolved issue about CB is the functional role of alternative splicing of its mRNA, giving rise to three main isoforms differing exclusively in the C-terminal domain (CB1-3) and having or lacking an SH3 domain close to the N-terminus. While the latter is thought to regulate the catalytic activity of CB, the specific functions of the CB1-3 isoforms are currently not understood [15]. CB1, CB2 and CB3 have previously been shown to exert comparable effects on postsynaptic gephyrin clustering when overexpressed in primary neurons [18]

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