Adherens Junctions Are Required for Maintaining Both Germline and Somatic Stem Cells in their Niches in the Drosophila Ovary. T. Xie , X. Song , C. Zhu , C. Doan. Stowers Inst, 1000 East 50th St. Kansas City, MO 64110.

   Stem cells have been suggested to be located in specialized microenvironments or niches in the varieties of systems. Germline stem cells (GSCs) in the Drosophila ovary have been recently shown to be located in a niche. To further understand how the niche might regulate GSCs, we have sought to investigate how these stem cells are anchored in their niches. Here we report that two major components of adherens junctions, E-Cadherin and b-Catenin encoded by shotgun (shg) and armadillo (arm), respectively, are essential for anchoring both GSCs and somatic stem cells (SSCs) in their niches. Shg and Arm proteins are localized to the junctions that form between GSCs and their neighboring cells, Cap cells. The results from our mutant clonal analysis have indicated that GSCs carrying homozygous mutations for shg and arm turn over much more quickly than wild type ones. Since Arm is also involved in wg and wg-like signaling pathways, we showed by performing mutant clonal analysis of sgg and dsh that wg and wg-like signaling pathways do not directly regulate GSCs. These results support that GSCs loss caused by arm mutations is due to the disruption of adherens junction function rather than wg-like signaling pathways. Furthermore, we have observed that adherens junctions form at the initial recruitment of GSCs to their niches, suggesting that E-cadherin-mediated cell-cell adhesion is also required for stem cell homing. Finally, we have also shown that both Shg and Arm are also essential for anchoring SSCs. Therefore, we conclude that adherens junctions are essential for anchoring GSCs and SSCs in the Drosophila ovary.