The molecular mechanisms regulating niche signal distribution in Drosophila germline stem cell niche.

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Stem cell posses the remarkable characteristics to produce its daughter cell that retain a stem-cell identity and the other that differentiates. Stem cells reside in dedicated cellular microenvironments termed stem-cell niches. These niches dictate a stem-cell identity, maintain the stem cell population, and coordinate proper homeostatic production of differentiated cells. Drosophila germ line stem cells(GSCs) are one of the ideal models for stem cell study in vivo. In apical tips of both male and female gonads, GSCs associate with specially differentiated somatic gonadal cells, the niche cells. These niche cells generate niches for GSCs by secreting signaling molecules. Although these facts indicate that region of niche is defined by the spatial distribution of these ligands, molecular mechanisms that regulate ligand distribution within the niche is not characterized.In this study, we showed that Drosophila Heparan Sulfate Proteoglycans(HSPGs) are essential components of GSC niche. Drosophila two glypians, a subfamily of HSPGs, were expressed in niche cells of female and male gonads and were required for GSC maintenance. Conversely, when glypican was ectopically expressed in ovaries, we observed expansion of GSC niche. These results showed that these glypicans define niche region molecularly.