Bmp signals from niche cells directly repress transcription of a differentiation-promoting gene,bag of marbles, in germline stem cells in theDrosophilaovary

Abstract

The Drosophila ovary is an attractive system to study how niches control stem cell self-renewal and differentiation. The niche for germline stem cells (GSCs) provides a Dpp/Bmp signal, which is essential for GSC maintenance.

Genetic dissection of a stem cell niche: The case of the Drosophila ovary

“…2C), we thought that bab1-Gal4 might be useful for the ectopic expression of ligands in the stromal CpCs, TFCs, and IGS cells. To test this, we wanted to determine if bab1-Gal4-mediated expression of dpp could induce hyperplastic GSC growth, characterized by the presence of hundreds of spherical spectrosome containing GSC-like cells, which has previously been observed when dpp was expressed in FCs and IGS cells (Kai and Spradling, 2003;Zhu and Xie, 2003;Song et al, 2004;Xi et al, 2005). However, we found that ectopic expression of dpp when driven by bab1-Gal4 was lethal (data not shown).…”

“…On the basis of the results we have presented in this report, bab1-Gal4 makes the generation of stromal cell clones a practical proposition, and thus should allow several key questions about stem cell niches to be addressed. The ability to express transgenes specifically in anterior stromal cells may be useful to investigate the roles of other putative stem cell niche ligands such as Gbb (Song et al, 2004), Hh (King et al, 2001;Zhang and Kalderon, 2001;Zhu and Xie, 2003) or Upd (Decotto and Spradling, 2005). Moreover, we have shown that the combination of bab1-Gal4 with Gal80 ts affords the flexibility to test the effect of ectopic expression of transgenes without deleterious effects on early development.…”

“…Evidence from an enhancer trap reporter of a target of the BMP pathway, dad-lacZ, suggests that the BMP pathway may be activated in some anterior somatic IGS cells (Casanueva and Ferguson, 2004;Song et al, 2004; 6. A functional BMP pathway is not essential within CpCs for GSC maintenance.…”

“…However, other reports found dad-LacZ expressed in some IGS cells but not in the CpCs themselves (Song et al, 2004;Kirilly et al, 2005). To examine if the BMP pathway is functionally required in CpCs for GSC maintenance, we used bab1-Gal4 to drive the formation of mutant clones for the essential Smad effector, Mad (Raftery and Sutherland, 1999).…”

“…Germline mutant clones of downstream dpp-pathway components, such as tkv or Mad, result in the rapid loss of GSCs (Wong et al, 2005). The main target of the BMP signaling pathway appears to be the repression of bag-of-marbles (bam) McKearin, 2003, 2005;Casanueva and Ferguson, 2004;Song et al, 2004;Szakmary et al, 2005), whose expression is sufficient to induce GSC differentiation (Ohlstein and McKearin, 1997). Ectopic expression of dpp results in the formation of large GSClike tumors, suggesting that dpp is both necessary and sufficient to prevent GSC differentiation (Xie and Spradling, 1998).…”