Coordinating differentiation with behavioral output of the CCAP-neuron network in Drosophila melanogaster.

Appropriate integration of neurons into functioning networks is the ultimate goal of neuronal differentiation. My thesis examined the mechanism and timing of neuronal differentiation in Drosophila melanogaster in relation to the functional requirements of a developing neuronal network. Specifically, my thesis aimed to address the role of extrinsic signaling in inducing and maintaining the expression of genes important to the function of neurons within their network. CCAP-neurons were chosen as a model because: 1) GAL4 drivers are available for cell-specific genetic manipulation. 2) The critical role of CCAP-neurons in the behavior, ecdysis, provides for an easily assayed phenotype if these neurons fail to function properly. 3) Four peptide hormones are selectively expressed in differentiated CCAP-neurons that are essential for the normal function of CCAP-neurons in ecdysis; this provides a direct link between gene expression and behavior. 4) Ecdysis is reiterated at multiple developmental steps, thus the CCAP-neuronal population functions throughout development. Together, these factors allow my work to relate neuronal subtype-specific differentiation to the regulation of gene expression and then directly to behavior. Larval Drosophila CCAP-neurons comprise ~46 neurons [~36 interneurons (CCAP-INs) and 10 efferent-neurons (CCAP-ENs)] that express a number of terminal differentiation genes (TDGs; such as neuropeptides). To begin, we delineated mechanisms underlying the expression of four TDGs, the peptide hormones CCAP, MIP, Bursicon-α and Bursicon-β, which together mediate the functional output of those neurons. Importantly, my studies found that a specific subset of CCAP-neurons, the CCAP-ENs, is both necessary and sufficient for ecdysis, and that their function in ecdysis is mediated by extrinsic BMP-dependent peptide hormone expression. Additionally, we found that the change in the ecdysis behavioral sequence from larval to pupal ecdysis is supported by the recruitment of a ‘late’ subset of CCAP-neurons that are born in the embryo but undergo extrinsic ecdysone-triggered, temporally-tuned differentiation immediately prior to pupal ecdysis.Medicine, Faculty ofGraduat