Protein synthesis and degradation are essential to regulate germline stem cell homeostasis in Drosophila testes

The homeostasis of self-renewal and differentiation in stem cells is strictly controlled by intrinsic signals and their niche. We conducted a large-scale RNA interference (RNAi) screen in <i>Drosophila</i> testes and identified 221 genes required for germline stem cell (GSC) maintenance or differentiation. Knockdown of these genes in transit-amplifying spermatogonia and cyst cells further revealed various phenotypes. Complex analysis uncovered that many of the identified genes are involved in key steps of protein synthesis and degradation. A group of genes that are required for mRNA splicing and protein translation contributes to both GSC self-renewal and early germ cell differentiation. Loss of genes in protein degradation pathway in cyst cells leads to testis tumor with overproliferated germ cells. Importantly, in the Cullin 4-Ring E3 ubiquitin ligase (CRL4) complex, we identified multiple proteins that are critical to GSC self-renewal. pic/DDB1, the linker protein of CRL4, is not only required for GSC self-renewal in flies but also for maintenance of spermatogonial stem cells (SSCs) in mice.

干细胞自我更新与分化的稳态严格受内在信号及其微环境（niche）调控。我们在果蝇（Drosophila）睾丸中开展了大规模RNA干扰（RNA interference，RNAi）筛选，鉴定出221个对生殖系干细胞（germline stem cell，GSC）的维持或分化必需的基因。在过渡扩增精原细胞与囊细胞中敲低这些基因，进一步揭示了多种表型。综合分析显示，多数鉴定出的基因参与蛋白质合成与降解的关键步骤。一类参与mRNA剪接与蛋白质翻译的基因，同时参与GSC的自我更新与早期生殖细胞分化过程。在囊细胞中缺失蛋白质降解通路相关基因，会引发携带过度增殖生殖细胞的睾丸肿瘤。尤为重要的是，在Cullin 4环E3泛素连接酶（Cullin 4-Ring E3 ubiquitin ligase，CRL4）复合物中，我们鉴定出多个对GSC自我更新至关重要的蛋白质。作为CRL4的衔接蛋白，pic/DDB1不仅在果蝇中对GSC自我更新不可或缺，在小鼠中也对精原干细胞（spermatogonial stem cells，SSCs）的维持发挥关键作用。