Ecdysone regulation of molting and morphogenesis in Drosophila

High titer pulses of the steroid hormone ecdysone trigger the major developmental transitions during the Drosophila life cycle, including larval molting and metamorphosis. Ecdysone directs these complex biological events by initiating cascades of regulatory gene expression. While several components of these cascades have been identified, the connection between the regulatory genes and the processes they control are just beginning to be elucidated. To gain insight into the hormonal regulation of development, my work has focused on the identification of genes that function during larval molting and leg disc morphogenesis.; Leg disc morphogenesis is the process by which the flat larval leg disc obtains the general shape of an adult leg through coordinated cell shape changes. This process is triggered by the late larval ecdysone pulse and requires the function of ecdysone-inducible transcription factors and proteases, as well as components of the contractile cytoskeleton and adherens junction. In an effort to identify additional genes that are regulated by ecdysone and function during leg disc morphogenesis, I carried out a screen of lethal P-element insertion lines. This screen identified mutations in two ecdysone-inducible genes, bancal and vulcan. bancal encodes the Drosophila homologue of hnRNP K and may function to regulate gene expression at either the transcriptional or post-transcriptional level. vulcan encodes a putative component of the septate junction and may play a role in the maintenance of proper intercellular adhesion during morphogenesis.; During the ecdysone triggered process of molting, the outer cuticle of the larva is shed and replaced with a new cuticle that can accommodate additional growth. Defects in this process are often displayed by animals carrying mutations in components of the ecdysone signaling cascade. I have identified a novel component of this cascade, rigor mortis, which when mutated results in defects in molting and the ecdysone-regulated process of puparium formation. rigor mortis encodes a large protein that contains multiple WD-40 repeats as well as an LXXLL motif. The LXXLL motif has been shown in vertebrate systems to mediate binding to nuclear hormone receptors, suggesting that Rigor Mortis may function as a cofactor for one or more of the Drosophila receptors.