Many studies have focused on the mechanisms of stem cell maintenance via their interaction with a particular niche or microenvironment in adult tissues, but how formation of a functional niche is initiated, including how stem cells within a niche are established, is less well understood. Adult Drosophila melanogaster ovary Germline Stem Cell (GSC) niches are comprised of somatic cells forming a stack called a Terminal Filament (TF) and associated Cap and Escort Cells (CCs and ECs, respectively), which are in direct contact with GSCs. In the adult ovary, the transcription factor Engrailed is specifically expressed in niche cells where it directly controls expression of the decapentaplegic (dpp) gene encoding a member of the Bone Morphogenetic Protein (BMP) family of secreted signaling molecules, which are key factors for GSC maintenance. In larval ovaries, in response to BMP signaling from newly formed niches, adjacent primordial germ cells become GSCs. The bric-à-brac paralogs (bab1 and bab2) encode BTB/POZ domain-containing transcription factors that are expressed in developing niches of larval ovaries. We show here that their functions are necessary specifically within precursor cells for TF formation during these stages. We also identify a new function for Bab1 and Bab2 within developing niches for GSC establishment in the larval ovary and for robust GSC maintenance in the adult. Moreover, we show that the presence of Bab proteins in niche cells is necessary for activation of transgenes reporting dpp expression as of larval stages in otherwise correctly specified Cap Cells, independently of Engrailed and its paralog Invected (En/Inv). Moreover, strong reduction of engrailed/invected expression during larval stages does not impair TF formation and only partially reduces GSC numbers. In the adult ovary, Bab proteins are also required for dpp reporter expression in CCs. Finally, when bab2 was overexpressed at this stage in somatic cells outside of the niche, there were no detectable levels of ectopic En/Inv, but ectopic expression of a dpp transgene was found in these cells and BMP signaling activation was induced in adjacent germ cells, which produced GSC-like tumors. Together, these results indicate that Bab transcription factors are positive regulators of BMP signaling in niche cells for establishment and homeostasis of GSCs in the Drosophila ovary.

许多研究都集中于通过干细胞与成人组织中特定生态位或微环境的相互作用来维持干细胞的机制，但是人们对如何启动功能生态位的形成（包括如何在生态位中建立干细胞）的了解较少。成年果蝇卵巢生殖干细胞（GSC）壁ches由体细胞组成，形成一个称为末端细丝（TF）的栈以及与Cap和Escort细胞（分别为CC和EC）（直接与GSC接触）形成的堆栈。在成年卵巢，转录因子ENGRAILED具体利基细胞，其中它直接控制的表达表达decapentaplegic（DPP）编码分泌信号分子的骨形态发生蛋白（BMP）家族成员的基因，这是维持GSC的关键因素。在幼虫卵巢中，响应于新形成的壁B的BMP信号传导，相邻的原始生殖细胞成为GSC。在金砖四国小古玩旁系同源（bab1和bab2）编码含有BTB / POZ结构域的转录因子，这些转录因子在幼虫卵巢发育的壁ni中表达。我们在这里表明，在这些阶段中，它们的功能对于TF形成的前体细胞特别必要。我们还为幼虫卵巢中GSC的建立和成年后GSC的稳健维护开发了适当位置的Bab1和Bab2的新功能。此外，我们表明，利基细胞中Bab蛋白的存在对于激活报告dpp表达的转基因是必需的，否则在其他正确指定的Cap细胞中，幼虫阶段的dpp表达独立于Engrailed及其同系物（En / Inv）。而且，大大减少了纠缠/被感染幼虫阶段的表达不损害TF的形成，仅部分降低GSC数量。在成年卵巢中，db报告基因在CC中表达也需要Bab蛋白。最后，当bab2在该位以外的体细胞中此阶段过表达时，没有检测到异位En / Inv水平，但是在这些细胞中发现了dpp转基因的异位表达，并且在邻近生殖细胞中诱导了BMP信号激活。 ，产生了GSC样肿瘤。在一起，这些结果表明Bab转录因子是在果蝇卵巢中GSCs的建立和稳态的利基细胞中BMP信号的正向调节剂。