Practice question

Drosophila germarium contains germline stem cells anchored to somatic cap cells forming stem cell niche at anterior tip. Cap cells secrete Decapentaplegic, fly BMP2/4 ortholog, activating TGF-beta receptors thickveins and punt on adjacent germline stem cell. Ligand binding phosphorylates Mad, homolog of Smad1, which partners with Medea to repress transcription of differentiation factor bag-of-marbles called bam. Repression maintains self-renewal and prevents cystoblast formation and meiosis entry. When daughter cell moves away from source, BMP signal declines, bam derepressed triggering differentiation into cystocyte. JAK-STAT maintains somatic niche cells, Notch and FGF not primary differentiation inhibitors here for germline.