I’m a homebody. I admit it. We’re all supposed to be adventurous, live on the edge, blah blah blah….but I thrive at home with my family around me. Maybe this makes me more like a stem cell than you glamorous jet-setters out there, and that seems pretty okay to me. Stem cells must stay in their niche, and a recent paper shows how some stem cells in the fruit fly do this through regulation of asymmetric division.
When adult stem cells divide, they produce a daughter cell that will take on a specific cell fate and another stem cell. To maintain this stem cell identity a stem cell must stay within its niche, or its microenvironment. In the fruit fly testes, germline stem cells (GSCs) stay adjacent to the “hub” within their niche and divide asymmetrically. In these divisions, a centrosome is positioned near the hub-GSC interface, and this aligns the mitotic spindle perpendicular to the hub. After cell division, the daughter cell that will remain a stem cell maintains its hub-GSC interface, while the differentiating cell is positioned further away. A recent paper shows that poor nutrient conditions prevent proper centrosome positioning in GSCs, which causes a delay in cell division via the centrosome orientation checkpoint. Roth and colleagues show that centrosome orientation is regulated by the insulin receptor pathway through its effect on the localization of Apc2, a cortical anchor for GSC centrosomes. The image above shows GSCs surrounding the hub (star) in a fruit fly testes cultured in poor nutrient conditions. One cell has correct centrosome orientation (yellow circle, centrosomes are red dots), while two cells (white circle) have misoriented centrosomes (arrowheads).
BONUS! Aren't GSCs pretty!? Check out these other posts on GSCs (here and here) that I wrote last week.
Roth, T., Chiang, C., Inaba, M., Yuan, H., Salzmann, V., Roth, C., & Yamashita, Y. (2012). Centrosome misorientation mediates slowing of the cell cycle under limited nutrient conditions in Drosophila male germline stem cells Molecular Biology of the Cell, 23 (8), 1524-1532 DOI: 10.1091/mbc.E11-12-0999