Cover Story 2015, Volume 10 Issue 1
The Drosophila testis is an easily accessible system for analysis of stem cell dynamics and was one of the earliest examples of in vivo demonstration of a stem cell niche. An antibody directed against the Vasa protein (red) illustrates germ cells within the testis. Germline stem cells present in the apical tip of the testis are attached in a ring to somatic hub cells. The hub cells express high levels of E-cadherin (blue) that function in adherens junctions to maintain attachement of the stem cells. The germline stem cells divide asymmetrically to renew themselves and generate a gonialblast committed to differentiation. The gonialblast undergoes four rounds of mitosis to produce a cyst of 16 interconnected spermatogonia that differentiate into spermatocytes. The germline stem cells, gonialblasts and 2-cell cysts of spermatogonia strongly express the held-out-wings RNA-binding protein (green). Prior to undergoing meiosis, spermatocytes increase in volume 25-fold. The stem cell niche consists of post-mitotic somatic hub cells and mitotic cyst progenitor cells. The cyst progenitor cells not only produce niche signals that regulate differentiation of the germline stem cells but are also themselves stem cells. Cyst progenitor cells divide asymmetrically to renew themselves and generate post-mitotic cyst cells that continue to nourish and regulate differentiation of the cyst of interconnected germ cells. The value of this system to the field of stem cell biology lies in the simple cytoarchitecture of the niche and the exquisite genetic analysis that can be performed in Drosophila. Thanks to Adrian Monk for providing the image. (See pages 1-10 by Gary R. Hime et al. for more information)[Detail] ...