Li and Xie, Ann. Rev. Dev. Biol. 2005, 605-663

Upd (unpaired)  from the hub activates the JAK-STAT pathway in GSCs and promotes their self- renewal (Kiger et al. 2001, Tulina & Matsunis 2001). Additionally, the activation of JAK- STAT signaling can reprogram mitotic germ cysts into GSCs (Brawley & Matunis 2004). As in the ovary, BMP signaling is required for controlling GSC self-renewal in the testis (Kawase et al. 2004, Schulz et al. 2004,

Shivdasani & Ingham 2003). Hub cells and somatic cyst cells express gbb at high levels and dpp at much lower levels; consequently, BMP downstream components are essential for controlling testicular GSC self-renewal (Kawase et al. 2004). Because dpp overexpres- sion fails to suppress completely spermatogo- nial cell differentiation, BMP signaling likely plays a permissive role in controlling male GSC self-renewal. BMP and JAK-STAT sig- naling pathways are required for controlling male GSC self-renewal; thus, they must some- how interact with each other. The integra- tion between these two pathways in male GSCs is an important area in need of future exploration.