Ecdysone regulation of gene expression during Drosophila melanogaster development

by 1974- Davis, Melissa Boneta

Pulses of the steroid hormone ecdysone punctuate each stage of the Drosophila melanogaster life cycle. The ecdysone signal is transduced to the genomic level via the Ecdysone Receptor Complex, made up of one of three EcR isoforms and a heterodimeric partner, USP. In this work, we show that the EcR isoforms have distinct developmental functions, based on the unique mutant phenotype of the EcR-A mutants in comparison to the EcR-B1 mutants (Chapter 2). While EcR-B1 is required for pupariation, the EcR-A isoform is required for completion of pupal development. The nature of the EcR-A mutant deletions also revealed some variation in the phenotypes. This observation, in conjunction with a putative novel EcR-A isoform further substantiates the hypothesis of the EcR isoforms having unique functions. We employed a genomics approach to ascertain a novel set of ecdysone targets. We focused on a specific pulse of ecdysone which occurs in the middle of the third instar, which we refer to as the mid-third instar commitment pulse (Chapter 3). We show there are many ecdysone regulated genes which have a diverse expression pattern during this pulse, substantiating the presence of an ecdysone pulse at this timepoint. We identified several genes that are considered ecdysone target candidates based on their expression patterns. This work contributes more detail to the elucidation of the ecdysone signaling pathway, and also lends a template for the identification of gene targets in vertebrate steroid pathways.