Drosophila Embryonic Type II Neuroblasts: Origin, Temporal Patterning and Contribution to the Adult Central Complex
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The large numbers of neurons that comprise the adult brain display an immense diversity. Repeated divisions of a relatively small pool of neural stem cells generate this neuronal diversity during development. To increase progress towards medical treatments for neurodegenerative diseases, it is of interest to understand both how neural stem cells generate the assortment of neurons and how these neurons come together to form a functional brain. Brain assembly occurs sequentially across time with early events laying the foundation for later events. Drosophila neural stem cells, neuroblasts (NBs), are an excellent model for investigating how neural diversity is generated and what roles early and late born neurons have in shaping the stereotypical adult brain structure. Generation of neural diversity, begins with specifying the diverse population of stem cells, called spatial patterning, and continues with diversifying neurons made from the diverse stem cells, called temporal patterning. Drosophila NBs exhibit both spatial and temporal patterning. Drosophila NBs have three types of division modes: type 0, type I and type II. Type II NBs expand the number of neurons made with progeny that exhibit a transit-amplifying division pattern, similar to that of mammalian outer subventricular zone (OSVZ) progenitors. Additionally, type II NBs exhibit temporal patterning across both the NB and their progeny to generate a large diversity of neurons that populate a conserved region of the brain responsible for many sensory and motor functions, called the central complex. Type II NBs have only been identified and studied during later stages in development, with nothing known about their origin or early divisions. In this dissertation, I describe the early lineages of the type II NBs within the Drosophila embryo. I show that type II NBs and lineages originate early in development, exhibit temporal patterning across both the NB and transit-amplifying progeny, and produce neurons that survive into the adult brain to innervate and potentially serve as a foundation within the adult central complex. Additionally, I explain how live imaging of the developing Drosophila brain can answer questions not easily addressed through other methods.