The Establishment Of Spermatogonial Stem Cell Xenotransplantation System And Regulation Of Early Spermatogenesis

Germ cells are main players of mammalian reproduction,in which spermatogonia stem cells(SSCs)are crucial for postnatal germ cell development,a process called spermatogenesis.In this study,we investigated the SSC properties and regulations from two aspects:xenotransplantation of SSCs and regulation of subcellular organelle interactions in early spermatogenesis.We first explored the effect of mouse testicular microenvironment on human spermatogonial stem cells(h SSCs)through xenotransplantation.We found that injected human spermatogonia could survive in the testis of nude mice,ICR mice and c-kit W/W^vmice,and could migrate to the basal membrane of seminiferous tubules,thus exhibiting the functional characteristics of SSCs.Therefore,these data suggest that microenvironment in mouse testes can provide a suitable niche for h SSC colonizations without immunological rejection.The h SSC xenotransplantation system provides a new platform for the functional confirmation of spermatogonium-like cells from pluripotent stem cells,and also offers a new way for the h SSC preservation.In the 2^nd part of the study,we explore the germline regulation in functions of mitochondria and endoplasmic reticulum(ER).We found that mitofusins(MFNs)or ASZ1 deficiency affects spermatogonial differentiation.In addition,MFNs preferentially regulate mitochondrial and ER functions via mitochondrial-associated membranes(MAM)in certain cell types.Conditional knockout Mfns in germ cells increase the expression of unfolded protein response and activate the ER stress.More interestingly,we found that germ cell-specific protein ASZ1 interacts with MFNs to impact the mitochondrial and ER functions.To understand the germ cell regulation of mitochondrial functions,we identified potential MFN interacting proteins in germ cells.We also isolated MAMs and will futher determine the composition of protein complex at MAMs through mass spectrometry.This will advance our knowledge how mitochondrial and ER functions are spercifically regulated in early spermatogenesis.