Department of Biological Sciences/RNA Institute, University at Albany SUNY, Albany, New York, United States of America.
Albany Medical College, Albany, New York, United States of America.
PLoS Genet. 2018 Jan 25;14(1):e1007154. doi: 10.1371/journal.pgen.1007154. eCollection 2018 Jan.
Germline stem cell (GSC) self-renewal and differentiation into gametes is regulated by both intrinsic factors in the germ line as well as extrinsic factors from the surrounding somatic niche. dWnt4, in the escort cells of the adult somatic niche promotes GSC differentiation using the canonical β-catenin-dependent transcriptional pathway to regulate escort cell survival, adhesion to the germ line and downregulation of self-renewal signaling. Here, we show that in addition to the β-catenin-dependent canonical pathway, dWnt4 also uses downstream components of the Wnt non-canonical pathway to promote escort cell function earlier in development. We find that the downstream non-canonical components, RhoA, Rac1 and cdc42, are expressed at high levels and are active in escort cell precursors of the female larval gonad compared to the adult somatic niche. Consistent with this expression pattern, we find that the non-canonical pathway components function in the larval stages but not in adults to regulate GSC differentiation. In the larval gonad, dWnt4, RhoA, Rac1 and cdc42 are required to promote intermingling of escort cell precursors, a function that then promotes proper escort cell function in the adults. We find that dWnt4 acts by modulating the activity of RhoA, Rac1 and cdc42, but not their protein levels. Together, our results indicate that at different points of development, dWnt4 switches from using the non-canonical pathway components to using a β-catenin-dependent canonical pathway in the escort cells to facilitate the proper differentiation of GSCs.
生殖细胞干细胞 (GSC) 的自我更新和分化为配子，既受到生殖系中内在因素的调节，也受到周围体腔细胞外基质的外在因素的调节。成年体腔细胞外基质中的 escort 细胞中的 dWnt4 通过经典的β-catenin 依赖性转录途径促进 GSC 分化，从而调节 escort 细胞的存活、与生殖系的黏附和自我更新信号的下调。在这里，我们表明，除了β-catenin 依赖性经典途径外，dWnt4 还利用 Wnt 非经典途径的下游成分来更早地促进 escort 细胞功能。我们发现，下游非经典成分 RhoA、Rac1 和 cdc42 在雌性幼虫性腺的 escort 细胞前体中表达水平较高且活性较高，与成年体腔细胞外基质相比。与这种表达模式一致，我们发现非经典途径成分在幼虫阶段发挥作用，而在成年阶段不发挥作用，以调节 GSC 分化。在幼虫性腺中，dWnt4、RhoA、Rac1 和 cdc42 需要促进 escort 细胞前体的混合，这一功能随后促进了成年 escort 细胞的正常功能。我们发现，dWnt4 通过调节 RhoA、Rac1 和 cdc42 的活性而不是它们的蛋白水平来发挥作用。总之，我们的结果表明，在不同的发育阶段，dWnt4 在 escort 细胞中从使用非经典途径成分切换到使用β-catenin 依赖性经典途径，以促进 GSCs 的适当分化。
