MECHANISMS OF CELL REARRANGEMENT AND CELL RECRUITMENT IN DROSOPHILA OVARY MORPHOGENESIS AND THE REQUIREMENT OF BRIC-A-BRAC

The Drosophila ovary consists of repeated units, the ovarioles, where oogenesis takes place. The repetitive structure of the ovary develops de novo from a mesenchymal cell mass, a process that is initiated by t he formation of a two-dimensional array of cell stacks, called termina l filaments, during the third larval instar. We have studied the morph ogenetic process leading to the formation of terminal filaments and fi nd that this involves recruitment, intercalation and sorting of termin al filament cells. Two other types of cell stacks that participate in ovary morphogenesis, the basal stalks and interfollicular stalks, also form by cell rearrangement utilizing a convergence and extension mech anism. Terminal filament formation depends on the Bric a brac protein, which is expressed in the nuclei of terminal filament cells and is ce ll autonomously required. Disruption of terminal filament formation, t ogether with defects of basal and interfollicular stalk development, l eads to disruption of ovariole formation and female sterility in bric a brac mutants.