Snail controls proliferation of Drosophila ovarian epithelial follicle stem cells, independently of E-cadherin

Epithelial stem cells undergo constant self-renewal and differentiation to maintain the homeostasis of epithelial tissues that undergo rapid turnover. Recent studies have shown that the epithelial-mesenchymal transition (EMT), which is primarily mediated by Snail via the suppression of E-cadherin, is able to generate cells with stem cell properties. However, the role of Snail in epithelial stem cells remains unclear. Here, we report that Snail directly controls proliferation of follicle stem cells (FSCs) in Drosophila females. Disruption of Snail expression in FSCs compromises their proliferation, but not their maintenance. Conversely, FSCs with excessive Snail expression display increased proliferation and lifespan, which is accompanied by a moderate decrease in the expression of E-cadherin (required for adhesion of FSCs to their niche) at the junction between their adjacent cells, indicating a conserved role of Snail in E-cadherin inhibition, which promote epithelial cell proliferation. Interestingly, a decrease in E-cadherin in snail-knock down FSCs does not restore the decreased proliferation of snail-knock down FSCs, suggesting that adhesion strength of FSCs to their niche is dispensable for Snail-mediated FSC division. Our results demonstrate that Snail controls epithelial stem cell division independently of its known role in the EMT, which contributes to induction of cancer stem cells.