Excel file of soma versus germline TRAP analysis.

Gap junctions allow the exchange of small molecules between cells. How this function could be used to promote cell growth is not yet fully understood. During Drosophila ovarian follicle development, germ cells, which are surrounded by epithelial somatic cells, undergo massive growth. We found that this growth depends on gap junctions between these cell populations, with a requirement for Innexin4 and Innexin2, in the germ cells and the somatic cells, respectively. Translatomic analyses revealed that somatic cells express enzymes and transporters involved in amino acid metabolism that are absent in germ cells. Among them, we identified a putative amino acid transporter required for germline growth. Its ectopic expression in the germline can partially compensate for its absence or the one of Innexin2 in somatic cells. Moreover, affecting either gap junctions or the import of some amino acids in somatic cells induces P-bodies in the germ cells, a feature usually associated with an arrest of translation. Finally, in somatic cells, innexin2 expression and gap junction assembly are regulated by the insulin receptor/PI3K kinase pathway, linking the growth of the two tissues. Overall, these results support the view that metabolic transfer through gap junction promotes cell growth and illustrate how such a mechanism can be integrated into a developmental program, coupling growth control by extrinsic systemic signals with the intrinsic coordination between cell populations.间隙连接（gap junction）可介导细胞间小分子物质的交换，但其介导的该功能如何促进细胞生长的具体机制目前尚未完全阐明。在果蝇卵巢卵泡发育进程中，被上皮体细胞包裹的生殖细胞会经历大规模的生长过程。本研究发现，该生长过程依赖于两类细胞群之间的间隙连接，且分别需要生殖细胞中的Innexin4与体细胞中的Innexin2。翻译组学（translatomic）分析结果显示，体细胞可表达生殖细胞中缺失的、参与氨基酸代谢的酶类与转运蛋白。在此类分子中，我们鉴定出一种假定的氨基酸转运蛋白，其为生殖系生长所必需；该蛋白在生殖系中的异位表达，可部分弥补其自身缺失或是体细胞中Innexin2缺失所导致的生长缺陷。此外，干扰间隙连接功能或是抑制体细胞中部分氨基酸的摄入过程，均会诱导生殖细胞内形成P小体（P-bodies）——这一特征通常与翻译停滞状态相关。最后，体细胞中Innexin2的表达与间隙连接的组装过程，受胰岛素受体/PI3K激酶通路调控，进而将两种组织的生长进程关联起来。综上，本研究结果支持“通过间隙连接进行的代谢物质转运可促进细胞生长”这一学术观点，并阐明了此类机制如何整合至发育程序中，将外源系统信号介导的生长调控与细胞群间的内在协同过程相耦合。