Which factor prevents differentiation in Drosophila germline stem cells (GSCs)?
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.
Ref: Xie and Spradling, Science 1998, BMP Maintains Drosophila Germline Stem Cells.