Sperm stem cells have a lot riding on their success. Not only must they produce the actual sperm, but they must maintain a life-long supply. So, the self-renewal of spermatogonial stem cells is a finely-tuned talent of these stem cells. A recent paper in the Journal of Cell Science describes the role of Wnt signaling in spermatogonial stem cell maintenance.
Stem cells possess two key properties that make them so special – the ability to produce different types of specialized cells, and the ability for self-renewal. As spermatogonial stem cells (SSCs) must provide a life-long supply of sperm, their self-renewal is very important. Recently, a group looked at SSC maintenance and found a role for Wnt signaling in the process. Yeh and colleagues used clusters of SSCs in vitro to show that Wnt5a promotes the maintenance of SSCs as a cell-extrinsic factor, and functions independently of B-catenin signaling. Although Wnt5a does work independently of B-catenin in many diverse examples, this paper is the first to show this non-canonical pathway functioning in stem cell maintenance. Yeh and colleagues also found that Wnt5a is expressed in vivo in cells of the testes in newborn mice. Finally, SSC clusters expressed the Wnt5a receptors Fzd5, Fzd7 and Ror2. In the images above, Wnt5a gene expression (red) is found in Sertoli cells (green), which serve as “nurse” cells in the testes.
Yeh JR, Zhang X, & Nagano MC (2011). Wnt5a is a cell-extrinsic factor that supports self-renewal of mouse spermatogonial stem cells. Journal of cell science, 124 (Pt 14), 2357-66 PMID: 21693582