Elucidating the mechanism of asymmetric division within the epithelial follicle stem cell niche

Adult stem cells are maintained through the action of a specialized microenvironment, or niche, that facilitates asymmetric division. Detailed studies of the Drosophila male and female germline stem cell niches have provided valuable insight into the mechanism by which asymmetric stem cell division occurs in vivo. However, less is known about somatic stem cell niches in Drosophila and it is unclear whether somatic stem cells use a similar mechanism to self-renew. We used the epithelial follicle stem cells (FSCs) in the Drosophila ovary as a model for understanding the mechanism of asymmetric division in an epithelial stem cell. Precisely two follicle stem cells per germarium reside in defined locations against the basement membrane at the anterior edge of the tissue. Loss of components of the Bone morphogenetic protein (Bmp) and Wingless (Wg) pathways from FSCs causes rapid loss from the niche, indicating that these pathways are required for self-renewal (Kirilly et al, 2005). We found that loss of components of the Epidermal Growth Factor Receptor (EGFR) pathway causes early follicle cell differentiation defects. These findings have led us to study the involvement of the Bmp, Wg and EGFR pathways in the regulatory mechanism of FSC asymmetric division. Here we investigate whether EGF signaling promotes asymmetric FSC division through regulation of follicle cell differentiation and cell polarity via either the Bmp or Wg pathways. These findings will further our understanding of asymmetric division in an epithelial niche.