Nutrient-dependent regulation of neural stem cell proliferation and neural circuit formation

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Our brain is composed of an immense diversity of neurons that are molecularly, morphologically, and functionally distinct. Understanding how this immense diversity of neuron types is generated and organized to allow us and other adult animals to carry out such a vast array of complex tasks and behaviors is of great importance. By far, most of the neurons in our adult brains are generated during development, either directly or indirectly from the cell divisions of a defined but, rather heterogeneous population of neural stem cells. Molecular differences exist among neural stem cells based on their location and neural stem cell themselves can change their intrinsic genetic programs over time. Research outlined in this proposal is geared towards better understanding of how neural stem cell extrinsic factors integrate with neural stem cell intrinsic factors to control numbers and types of neurons produced through time and space during development. In the Siegrist lab, we use the genetically tractable model organism, Drosophila melanogaster, to uncover the genetic pathways and molecular mechanisms regulating neural stem cell proliferation decisions, from quiescence to proliferation, and then termination once development is complete. Our research goals include gaining a better understanding of how dietary nutrient availability affects neural stem cell proliferation decisions. In Drosophila, different neural stem cells respond differently to dietary nutrient availability. Most enter and exit quiescence in a dietary nutrient- and PI3-kinase-dependent manner, except for a small subset. The neural stem cells that divide continuously independent of dietary nutrient availability are the neural stem cells that generate neurons important for memory and learning. Through genetic and single cell sequencing techniques, we are working to identify the intrinsic differences among these neural stem cell types that distinguish nutrient-dependence versus nutrient-independence. We are also working on determining how dietary nutrients consumed during development regulate neural stem cell temporal programs and thus types and numbers of neurons produced. Neural stem cells in Drosophila sequentially express a series of transcription factors over time that specify the neuron types produced at each cell division. Whether extrinsic factors, such as nutrient availability affects neuroblast intrinsic temporal programs is currently unknown. Finally, we are also working to map out the neural circuitry that regulates neural stem cell proliferation decisions in response to dietary nutrient availability. Altogether, the research outlined here will advance our understanding of neural stem cell proliferation control during development and how dietary nutrient availability affects types and numbers of neurons produced. These insights should stimulate new discoveries in translational stem cell research in the context of normal development and disease states.