We have recently found that a remarkable remodeling of the internal structure of the Drosophila ovary takes place at the end of the larval period. This is when the partitioning of the ovary into ovarioles is initiated by the formation of regularly spaced terminal filaments inside the ovary. Drawings of the 3rd instar larval ovary after terminal filament formation and of the anterior tip of an adult ovariole are shown below. Our major goal is to study the development of the ovary during larval stages and to understand how the terminal filaments arise. This work will be divided into three parts: 1. Detailed analysis of the morphogenesis of wild type larval ovaries using light and electron microscopy, enhancer trap markers and mosaic analysis. 2. Molecular and genetic characterization of bric-a-brac and fs(2)eoP.L3, two genes required for the proper formation of terminal filaments. 3. A screen for other genes that are involved in the development of the larval ovary. In addition to being required for terminal filament stack formation, bric-a-brac is also required during leg and antenna development. We have discovered that a bric-a-brac mutant fly has a homeotic transformation of distal tarsal segments to a segment 1 identity, and that this transformation is dependent on the dosage of the bric-a-brac gene. In addition, bric-a-brac is expressed in a discontinuous gradient along the proximal-distal axis of the developing leg. As the second part of this grant, we propose to determine how the bric-a-brac gradient of expression is formed and to identify genes that interact with bric-a-brac during leg development.
