From Transcription to Tubulogenesis: Insights from the Drosophila Ovary

Abstract

During Drosophila melanogaster oogenesis, subsets of the epithelial cells that surround each developing egg chamber undergo morphogenesis to form epithelial tubes, and the lumens of these tubes serve as molds for the dorsal appendage (DA) filaments of the mature eggshell. This process is a simple and tractable system for identifying and characterizing the cellular events and molecular mechanisms required for epithelial tube morphogenesis, or tubulogenesis. The work presented in this dissertation provides insight both into the upstream gene regulatory elements that set the stage and maintain control, and into the downstream molecular effectors that govern cell shape, order, and movement, throughout DA tubulogenesis. In Chapter I, I highlight the fundamental importance of cellular tubes and the intimate relationship between tube morphology and function, explain what we do and do not know about the cellular and molecular mechanisms that drive tubulogenesis, provide a detailed description of the process of DA tubulogenesis, and emphasize the advantages of DA tubulogenesis as a model for epithelial tubulogenesis. In Chapter II, I establish regulatory links, specifically in regard to DA tubulogenesis, between upstream transcription factors, such as Tramtrack69 and Mirror, and downstream effectors, such as Paxillin and Dynamin. In Chapter III, I focus specifically on the role of Dynamin and Dynamin-mediated endocytosis in DA tubulogenesis. I identify and characterize novel roles for Dynamin in epithelial tube closure, cell intercalation, and biased apical-luminal expansion. Furthermore, I provide evidence that Dynamin is regulating the levels and behavior of both E-Cadherin and Integrin-based cellular adhesions, and propose that Dynamin facilitates the aforementioned cellular, tubulogenic processes by regulating the turnover of cellular adhesions. Finally, in Chapter IV, I summarize the results of my graduate research, discuss how these results fit with and augment our current knowledge of epithelial tubulogenesis, and propose future experiments that would further delve into the specific roles and mechanisms by which conserved, downstream, tubulogenic effectors, such as Dynamin and Paxillin, drive epithelial tubulogenesis.