FIGURE 1:

Diagram of male and female germline stem cell niches. (A) At the apical tip in the Drosophila testis, GSCs attach to the hub cells, whereas their daughters, GBs, are displaced away from the hub. Centrosome orientation prepares for perpendicular spindle orientation; the mother centrosome (yellow asterisk) is consistently located near the hub, whereas the daughter centrosome (black asterisk) migrates toward the opposite side of the GSC. GSCs contain the spectrosome (red circle), which assumes a spherical morphology, whereas differentiating spermatogonia (SG) contain the fusome (red line), which is branched and runs through the ring canals. GSCs are encapsulated by a pair of CySCs. GBs and SG are encapsulated by a pair of CCs, progeny of CySCs. (B) In the germarium in the Drosophila ovary, GSCs attach to the cap cells, whereas their daughters, CBs, are displaced away from the cap cells. Although the centrosomes (asterisks) are not stereotypically oriented in female GSCs, the spectrosome (red circle) is located close to the cap cells, orienting the mitotic spindle. Cap cells and terminal filaments (TFs) provide niche signals to GSCs. Escort cells (not shown) exist in the germarium that closely associate with the GSCs and developing germ cells. Unlike CySCs, they do not normally proliferate or move along with the developing germ cells. However, they provide supportive signals for germ cell development, similar to CySCs and CCs in the testis.