Genetic Regulation of Drosophila Mushroom Body Neuroblast Neurogenesis by Notch and Eyeless

Neural stem cells are the building blocks of the developing brain. Without strict regulation of stem cell progenitors, errors in proliferation can arise, leading to disease. Understanding the genetic and molecular (intrinsic and extrinsic) mechanisms that underlie stem cell regulation is crucial to developing therapeutics to treat disease. In this dissertation, I investigated the role of two conserved neural stem cell regulatory genes, Eyeless and Notch in the regulation of Drosophila mushroom body neuroblasts (MBNBs). Chapter one begins with an in-depth review of mushroom body neuroblasts from their origins, neurogenic period regulation by intrinsic and extrinsic cues, and termination. I also proposed future directions that could expand our knowledge in the field of MBNB neurogenesis. Chapter two experimentally showed how loss of Notch signaling pathway affects mushroom body neuroblasts. We found that without Notch and its ligand Delta, MBNBs experience premature elimination due to misregulation of their early temporal factor Imp. MBNBs are lost early via apoptosis in Delta knockdown animals. Due to this premature loss of MBNBs and Notch signaling in the MBNB progeny, the resulting mushroom body structure is also severely disrupted. In addition, I investigated how Eyeless operates as a MBNB specific factor to create lineage specific differences between MBNBs and other CBNBs. This work has helped increase the understanding of how MBNBs maintain a longer Imp positive proliferative window. In chapter three, I investigated the role of the MBNB specific factor Eyeless in MBNB neurogenesis. I found that Ey functions to regulate MBNBs through late acting temporal factors Syncrip (Syp) and Ecdysone-induced protein 93 (E93). Loss of Ey signaling also leads to diminished ecdysone receptor (EcR) expression, a component key to proper timing of MBNB termination at the end of their neurogenic period. Without Ey, MBNBs experience defects in autophagic cell death, leading to their persistence into adulthood. I also found that errors in autophagy initiation in Ey knockdown animals may be due in part to decreased regulation of the master autophagy regulator microphthalmia inducing transcription factor (Mitf). This chapter reveals novel roles for Eyeless in regulating the termination of MBNBs. Chapter four summarizes findings for Eyeless and Notch in regulating MBNB neurogenesis and also summarizes future avenues of research. Overall, my work highlights how MBNBs are controlled by Notch and Eyeless in the fly brain and furthering our understanding of NSC regulation.