Date of Thesis

5-11-2016

Thesis Type

Honors Thesis (Bucknell Access Only)

Degree Type

Bachelor of Science

Department

Neuroscience

First Advisor

Elizabeth C. Marin

Abstract

Neural remodeling is a necessary stage in the development of many animals and has myriad mechanisms by which the nervous system can be subject to modification. Steroid hormonal regulation is a key factor in regulating these developmental changes in the central nervous system. A holometabolous insect, Drosophila melanogaster (the common fruit fly), undergoes complete metamorphosis and dramatic neural reorganization in development, and thus provides a useful model to elucidate the mechanisms of complex nervous system modifications. Ecdysone is the steroid hormone responsible for metamorphic changes in insect development, and it signals through its heterodimeric receptor EcR/USP. Lee and colleagues previously concluded that the B1 isoform of EcR is necessary for γ neuron remodeling in the Drosophila mushroom body (Lee et al. 2000). However, the authors observed remodeling defects in trans-heterozygous animals that lacked functional copies of both the EcRB1 and EcRB2 isoforms, and either EcRB1 or EcRB2 overexpression was sufficient to rescue these defects. Their results left open the possibility that both isoforms might play a role in normal neuronal remodeling. In addition, it was not clear whether reception of ecdysone serves to relieve repression of the remodeling program or whether it is necessary in order to activate it. In the following paper, we first demonstrate that our dicer2-enhanced RNAi method is reliable for genetic knockdown experiments. We then show that the EcRB1 isoform may not be necessary for γ neuron pruning although knockdown of usp via RNAi results in delayed γ neuron pruning under standard conditions and disruption of pruning at higher temperatures. Lastly, by overexpression of two dominant negative EcRB1 constructs, we report that γ neuron pruning is dependent on activation of target gene expression via ecdysone signaling.

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