The proteasome,an evolutionarily conserved proteolytic complex comprising the 20S core particle and 19S regulatory particles,performs both shared and distinct functions across various tissues and organs.Spermatogenesis,a highly complex developmental process,relies on proteasome activity at multiple stages to regulate protein turnover.In this study,we selected the 20S subunit PSMA1 and 19S regulatory subunit PSMD2 to investigate the potential functions of the proteasome in spermatogenesis.Using Psma1-EGFP and Psmd2-mCherry knock-in mouse models,we confirmed the expression of both subunits in all spermatogenic cell types,with pronounced presence in early germ cell development.To further clarify their functional significance,we specifically knocked out Psma1 and Psmd2 in germ cells.Deletion of either PSMA1 or PSMD2 led to disrupted spermatogenesis,characterized by the complete absence of sperm in the epididymis.Subsequent analysis indicated that loss of these proteasome components impaired meiotic initiation.Psma1 and Psmd2 knockout germ cells showed accumulation of DMRT1,a key regulator of mitosis-to-meiosis transition,leading to a reduction in STRA8 levels and consequent disruption of meiosis initiation.This study sheds light on the molecular mechanisms that govern meiotic initiation and identifies potential genes associated with male infertility.
Ting-Ting HanLi-Ying WangQiu-Xing ZhouWei WeiYan-Jie MaYing-Hong ChenWei LiZhen-Yu JuChao Liu
The transition from mitosis to meiosis is a critical event in the reproductive development of all sexually reproducing species.However,the mechanisms that regulate this process in plants remain largely unknown.Here,we find that the rice(Oryza sativa L.)protein RETINOBLASTOMA RELATED 1(RBR1)is essential to the transition from mitosis to meiosis.Loss of RBR1 function results in hyper-proliferative sporogenous-celllike cells(SCLs)in the anther locules during early stages of reproductive development.These hyperproliferative SCLs are unable to initiate meiosis,eventually stagnating and degrading at late developmental stages to form pollen-free anthers.These results suggest that RBR1 acts as a gatekeeper of entry into meiosis.Furthermore,cytokinin content is significantly increased in rbr1 mutants,whereas the expression of type-B response factors,particularly LEPTO1,is significantly reduced.Given the known close association of cytokinins with cell proliferation,these findings imply that hyper-proliferative germ cells in the anther locules may be attributed to elevated cytokinin concentrations and disruptions in the cytokinin pathway.Using a genetic strategy,the association between germ cell hyper-proliferation and disturbed cytokinin signaling in rbr1 has been confirmed.In summary,we reveal a unique role of RBR1 in the initiation of meiosis;our results clearly demonstrate that the RBR1 regulatory module is connected to the cytokinin signaling pathway and switches mitosis to meiosis in rice.
CtBP-interacting protein(CtIP)is known for its multifaceted roles in DNA repair and genomic stability,directing the homologous recombination-mediated DNA double-stranded break repair pathway via DNA end resection,an essential error-free repair process vital for genome stability.Mammalian oocytes are highly prone to DNA damage accumulation due to prolonged G2/prophase arrest.Here,we explore the functions of CtIP in meiotic cell cycle regulation via a mouse oocyte model.Depletion of CtIP by siRNA injection results in delayed germinal vesicle breakdown and failed polar body extrusion.Mechanistically,CtIP deficiency increases DNA damage and decreases the expression and nuclear entry of CCNB1,resulting in marked impairment of meiotic resumption,which can be rescued by exogenous CCNB1 overexpression.Furthermore,depletion of CtIP disrupts microtubule-organizing centers coalescence at spindle poles as indicated by failed accumulation ofγ-tubulin,p-Aurora kinase A,Kif2A,and TPX2,leading to abnormal spindle assembly and prometaphase arrest.These results provide valuable insights into the important roles of CtIP in the G2/M checkpoint and spindle assembly in mouse oocyte meiotic cell cycle regulation.
Wei YueHong-Yong ZhangHeide SchattenTie-Gang MengQing-Yuan Sun
Meiosis is the process of producing haploid gametes through a series of complex chromosomal events and the coordinated action of various proteins.The mitochondrial protease complex(ClpXP),which consists of caseinolytic mitochondrial matrix peptidase X(ClpX)and caseinolytic protease P(ClpP)and mediates the degradation of misfolded,damaged,and oxidized proteins,is essential for maintaining mitochondrial homeostasis.ClpXP has been implicated in meiosis regulation,but its precise role is currently unknown.In this study,we engineered an inducible male germ cell-specific knockout caseinolytic mitochondrial matrix peptidase X(Clpx^(cKO))mouse model to investigate the function of ClpX in meiosis.We found that disrupting Clpx in male mice induced germ cell apoptosis and led to an absence of sperm in the epididymis.Specifically,it caused asynapsis of homologous chromosomes and impaired meiotic recombination,resulting in meiotic arrest in the zygotene-to-pachytene transition phase.The loss of ClpX compromised the double-strand break(DSB)repair machinery by markedly reducing the recruitment of DNA repair protein RAD51 homolog 1(RAD51)to DSB sites.This dysfunction may be due to an insufficient supply of energy from the aberrant mitochondria in Clpx^(cKO) spermatocytes,as discerned by electron microscopy.Furthermore,ubiquitination signals on chromosomes and the expression of oxidative phosphorylation subunits were both significantly attenuated in Clpx^(cKO) spermatocytes.Taken together,we propose that ClpX is essential for maintaining mitochondrial protein homeostasis and ensuring homologous chromosome pairing,synapsis,and recombination in spermatocytes during meiotic prophase I.
Hai-Wei FengYu ZhaoYan-Ling GaoDong-Teng LiuLi-Jun Huo
