Heparan sulfate proteoglycans in drosophila ovarian germline stem cell niche

The Drosophila female germline stem cell (GSC) niche at the anterior edge of the ovary provides a lifelong supply of germ cells for egg production. The GSC niche was the first to be characterized at the molecular level and is still one of the bestcharacterized examples of stem cell niches in any organism. Bone morphogenetic proteins (BMPs) produced by the niche cells only act on GSCs that are in a direct contact with the niche cells. This contact dependency is the basis for GSC asymmetric division, which produces both a GSC and a differentiating cell. Recent studies revealed the role of heparan sulfate proteoglycans in this spatially restricted BMP signaling. Dally, a Drosophila HSPG of the glypican type, is specifically expressed in the niche cells and activates BMP signaling in trans in directly contacting GSCs. Genetic and epigenetic control of dally gene transcription is an important aspect of GSC control. Further studies of stem cells in the genetically tractable model organism Drosophila will provide novel insights into the universal mechanisms by which the niche controls stem cell behaviors.