Stem cell niches are the microenvironments in which stem cells are produced and maintained. To capitalize on the potential therapeutic benefits of stem cells, we must define how they interact with their microenvironments and the regulatory mechanisms that govern their proliferation and differentiation. The Drosophila ovary germarium, in which female germline stem cells (GSCs) reside, is proving to be a valuable model system for characterizing such interactions. In a Commentary on p. 949, Acaimo González-Reyes reviews our understanding of the biology of this particular niche, focusing on work revealing the importance of cadherin adhesion molecules. Somatic `cap' cells in the niche release the TGFα-family protein DPP, which regulates GSC proliferation and differentiation. The architecture of the niche, however, appears to depend on DE-cadherin-mediated cell sorting. Studies of mosaic germaria containing wild-type GSCs and cadherin-mutant GSCs, for example, indicate that the presence of this cadherin on the GSCs allows them to adhere to the cap cells through formation of adherens junctions. This anchors them in the niche, where the microenvironment sustains their capacity to self-renew and divide asymmetrically.
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