EXPRESSION OF CONSTITUTIVELY ACTIVE NOTCH ARRESTS FOLLICLE CELLS AT APRECURSOR STAGE DURING DROSOPHILA OOGENESIS AND DISRUPTS THE ANTERIOR-POSTERIOR AXIS OF THE OOCYTE

During early development, there are numerous instances where a bipoten t progenitor divides to give rise to two progeny cells with different fates, The Notch gene of Drosophila and its homologues in other metazo ans have been implicated in many of these cell fate decisions. It has been argued that the role of Notch in such instances may be to maintai n cells in a precursor state susceptible to specific differentiating s ignals. This has been difficult to prove, however, due to a lack of de finitive markers for precursor identity. We here perform molecular and morphological analyses of the roles of Notch in ovarian follicle cell s during Drosophila oogenesis. These studies show directly that consti tutively active Notch arrests cells at a precursor stage, while the lo ss of Notch function eliminates this stage. Expression of moderate lev els of activated Notch leads to partial transformation of cell fates, as found in other systems, and we show that this milder phenotype corr elates with a prolonged, but still transient, precursor stage. We also find that expression of constitutively active Notch in follicle cells at later stages leads to a defect in the anterior-posterior axis of t he oocyte.