Figure 2

Signaling within the female germline stem cell niche. (a) Schematic illustrating that Decapentaplegic (Dpp) and Glass bottom boat (Gbb) produced in the anterior of the germarium binds to heterodimeric receptors on the surface of germline stem cells (GSCs). Activation of the receptor results in phosphorylation of Mad (pMad) which then partners with Medea and translocates into the nucleus, where it directly represses the transcription of bag of marbles (bam). This repression is relieved once a GSC daughter leaves the cap cell niche. Smurf, Fused, Brain tumor (Brat) and miR-184 all act to rapidly reduce bone morphogenetic protein (BMP) responsiveness within the cystoblast. Niche signaling is limited to the anterior of the germarium by Lsd1, which represses dpp expression outside the normal niche and by epidermal growth factor (Egf) signaling from the germline, which serves to limit dally expression in the escort cells. EGFR, epidermal growth factor receptor; JAK/STAT, Janus kinase/signal transducer and activator of transcription; pMad, phosphorylated Mothers Against Dpp; Tkv, Thickveins; YB, Female sterile (1) Yb. (b) Components of the extracellular matrix (ECM), including Viking (Vkg; red) and Division abnormally delayed (Dally; green) help to stabilize and limit BMP ligands (blue circles) within the anterior of the germarium. The adherens junction proteins Armadillo (Arm; brown) and Shotgun (Shg; grey) promote cell-cell adhesion between the cap cells (green) and GSCs (dark red).