Protein Synthesis And Degradation Are Critical To Regulate Germline Stem Cell Homeostasis In Drosophila Testes

The Drosophila testis is an ideal model for researchers to study germline stem cells(GSCs)and the process of spermatogenesis.The obtain of mature sperm depends on the normal self-renewal and differentiation of GSCs.Once the GSCs fail to self-renew and differentiate,it easily leads to either gonad developmental anomaly,or the loss of fertility,and even germ cell tumor,And further,the homeostasis of self-renewal and differentiation in stem cells is controlled by intrinsic signals and their niche.We conducted a large-scale RNA interference(RNAi)screen in Drosophila testes and identified 221 genes required for GSCs maintenance or differentiation.And these genes play different roles in many ways.For example,when some of those genes involving in transit-amplifying spermatogonia and cyst cells were knocked down respectively,we got various phenotypes of fly testis.By further bioinformational analysis,we get a regulatory network of GSCs in Drosophila testis.Then,we uncovered that many of the identified genes are involved in key steps of protein synthesis and degradation.And interestingly,we found a group of genes required for mRNA splicing and protein translation have dual functions.They not only contribute to GSCs self-renewal,but also play roles in early germ cell differentiation.What's more,loss of genes in the protein degradation pathway in cyst cells leads to testis tumors consisting of over-proliferated germ cells.Importantly,in the Cullin 4-RING E3 ubiquitin ligase(CRL4)complex,we identified multiple proteins that are crucial to GSC self-renewal,such as pic/DDB1,a CRL4 linker protein.And a series of tests suggested that CRL4 complex might be the only member among the CRL family that was involved in GSCs' self-renewal by mediating Nedd8.We further observed the testis developmental abnormal and the loss of germ cells in Ddb1 knockout mice.It indicated that pic/DDB1 is not only required for GSCs in flies but also required for maintenance of spermatogonial stem cells(SSCs)in mice.