Dissecting Synaptogenesis and Axonal Branching Mechanisms in Drosophila Melanogaster

Abstract

Axonal branching and synaptogenesis are critical mechanisms in neuronal development, enabling the formation of complex neural communication networks. Despite their importance, the specific regulatory factors and signaling pathways involved in these processes remain poorly understood. This dissertation aims to identify and elucidate these regulatory mechanisms. <br /> In a targeted genetic screening approach, I focused on Yorkie (Yki) downstream genes and identified Brain tumor (Brat) as one novel regulator of axonal branching and synapse modulation. Loss-of-function Brat MARCM analyses revealed a dosage-dependent effect of Brat on synaptogenesis, leading to either enhanced synapse formation or synapse depletion. These findings were corroborated by RNAi-mediated knock-down (K.D.) assays and null allele studies. <br /> In order to better study the molecular specialization of Yki in postmitotic neurons in thefuture, I adapted a <em>Drosophila Melanogaster</em> (<em>D.m.</em>) neuronal cell culture system (Bg3c2 cells) to investigate the effects of Yki overexpression in the central nervous system (CNS). My research uncovered that Yki localizes primarily within the nucleus, particularly enriched at the lamina, but is absent from the nucleolus. RNA-sequencing analysis of the effects of overexpressing a specific Yki isoform on gene expression revealed several novel potential target genes specifically regulated in postmitotic neurons, providing new insights into Yki signaling in CNS cells. <br /> This dissertation also explores the role of Cysteine-rich with EGF-like domain (Creld), a newly identified regulatory factor in axonal branching and synaptogenesis, that we previously found to play a role in mitochondria-ER contact sites (Paradis et al., 2022). Through a series of genetic molecular analyses, I demonstrate how Creld and Yki independently influence neuronal differentiation and metabolism. <br /> In conclusion, this dissertation advances our understanding of the complex regulatory networks governing neuronal development and function, highlighting the pivotal roles of Yki and Creld in these processes.