The Function Of Protein Prenylation In Spermatogonial Stem Cell Self-renewal And Differentiation Balance Regulation

The continuity of spermatogenesis depends on self-renewal and differentiation balance of spermatogonial stem cells(SSC)throughout the reproductive period in the mammalian testes.Both male and female gametes originate from primordial germ cells(PGCs).Male germ cells at puberty take on the dual task of maintaining spermatogonial stem cells and generating a continuous stream of sperm.Besides self-renewal as a population,undifferentiated spermatogonia generate differentiating spermatogonia,which then differentiate into meiotic spermatocytes,haploid spermatids and spermatozoa.Balance damage of SSC fate could impair testicular development and spermatogenesis afterward induce germ cell aplasia finally cause non-obstructive infertility.For male,Sertoli cell only(SCO)syndrome is a histopathologic phenotype displayed that the tubules are reduced in diameter,and contain only Sertoli cells but no spermatogonial cells involved in spermatogenesis.Regulation of SSC requires synergistic interaction of microenvironment factors and spontaneous response of germ cell.PI3K/Akt/mTORC1 signaling network is a critical rheostat for maintaining the homeostasis of stem cells has been reported relevant to the GDNF sensitivity,self-renewal and differentiation of SSC.And smallGTPase Rheb as an upstream regulation factor of mTORCl,which activation and location to endomembranes requires C-terminal C AAX modification by a farnesyl isoprenoid FPP,an intermediate of MVA pathway.GGPPS is a branch-point enzyme in the mevalonate pathway involved in the protein post-translational modification.GGPPS invert of geranylgeranyl diphosphate(GGPP)from farnesyl diphosphate(FPP),which are used for geranylgeranylation of proteins such as Ras and Ras-related small GTP-binding proteins with a CaaX motif at the C terminus and functions to regulate these proteins locate to the membrane.In study of spermatogenesis regulation,it has reported that total protein prenylation and the ratio of geranylgeranylated to farnesylated proteins both decreased during this same period,indicated dynamic balance of protein prenylation play an important role in spermatogenesis of rats during different periods.In our experiments,Ddx4-cre mice are used in generating conditional germ cell of ggpps knockouts in germ cell to studies male gametogenesis and infertility.We first found that ggpps germ cell specific knock out mice show imbalance GGPP/FPP level that displayed GGPP deficiency and FPP accumulation.Then we determined that adult Gc-ggpps-/-mice are high proportion infertile,and male mice represent Sertoli Cell Only phenotype during first round of spermatogenesis.Spermatogenesis failure happened at early stage displayed self-renewal decay and differentiation over-activation followed exhaust of spermatogonia stem cell and increased apoptosis of spermatocyte which cannot go through meiosis progress.Excessive accumulation of FPP induced Rheb over-farnesylation and activation,which cause mTORl signaling over activation in spermatogenic cell of Gc-ggpps-/-mice.We first hypothesis the fate of SSC maintain,self-renewal and differentiation,might be regulated by the dynamic balance between farnesylation/geranylgeranylation.Then we proved pretein isoprenylation of specific GTPase Rheb is an important cell-intrinsic regulator of differentiated fate determine via the mTORCl signaling pathway in SSCs.And we further propose that synergistic action between GGPP and FPP adjusting by GGPPS provides a time-conditioned dynamic balance between geranylgeranylation and farnesylation guide self-renewal and differentiating fate of SSC.We will further study the effect of protein prenylation on SSC to figure out possible molecular mechanism and effect genes of S SC self-renewal and differentiation fate determination.