The working model. In Drosophila ovarian stem cell niche, cap cells produce several signaling molecules including Dpp and Wnts. Dpp promotes GSC self-renewal by activating downstream (indicated by pMad). Wnts function in ECs via the canonical signaling pathway to promote Tkv expression, which in turn removes excess of cap cell–produced Dpp independent of the canonical Dpp signaling pathway and prevents Dpp activity outside the niche. Thus, the Drosophila GSC niche helps to define its own niche activity.