Effects Of Changes In The Hydrophobicity Of C. Elegans SMC-1 On Meiosis And Reproductive Aging

Reproductive aging is a major reproductive problem that plagues women,which is mainly reflected as the increased aneuploidy incidences of oocytes and embryos,and a significant increase in the probability of female infertility,miscarriage and birth defects.Previous studies have shown that mammalian reproductive senescence is closely related to the inability of oocytes to maintain a normal cohesin level during the prolonged meiotic prophase.Clarify the influence of gene mutations and other internal or external factors on meiotic cohesin maintenance and their underlying mechanisms will benefit the prevention and treatment of reproductive aging.The cohesin complex is a multi-subunit ring complex highly conserved across species.Three core components SMC1,SMC3 and an α-kleisin subunit interact to form a closed ring structure.Specifically,SMC3 interacts with kleisin N terminus to form the kleisin N gate,and SMC1 C-terminal domain interacts with kleisin C terminus through hydrophobic interaction to form kleisin C gate.With the assistance of SCC2-SCC4 complex,cohesin can be loaded onto the chromosomes through the kleisin N gate,holding sister chromatids together.Cohesin plays a variety of roles during meiotic progression,including homologous chromosome pairing,synapsis,recombination and DSB repair etc.During anaphase of cell division,cohesin dissociates from the chromosomes under the action of the anaphase-promoting complex or cyclosome(APC/C)and the separase,ensuring ordered chromosome segregation.With the advantages in genetics and cell biology study,Caenorhabditis elegans has become a unique model organism for studying meiosis and reproductive aging.In this study,we first revealed the correlation between cohesin disturbance and reproductive aging in a small-scale genetic screen.We found that when the C terminus of SMC-1 is fused with a GFP protein tag(smc-1::gfp),the worms exhibited reproductive aging phenotypes,including reduced brood sizes and elevated incidence of males among the progeny when the worms were old.In addition,we also observed aging related reduction in nucleus diameter during pachytene and decreased transcriptional activity during late prophase in smc-1::gfp worms.Interestingly,these phenotypes were not obvious when the m Cherry tag was fused to the C terminus of SMC-1.By analyzing protein sequences,we identified strong hydrophobic segments at the N-terminal and C-terminal regions of GFP,and such hydrophobic segments are not present in the m Cherry tag,suggesting that the hydrophobic segments in GFP tag may be a key factor affecting reproductive aging in smc-1::gfp worms.By analyzing human genetic variants,we discovered a set of missense mutations that change hydrophobic segment formation in SMC1.To verify whether these changes in hydrophobic segment formation will affect cohesin function and meiotic progression,we created three point mutant worm strains to simulate the hydrophobic changes seen in human cohesin.Among them,the mutants with enhanced hydrophobicity at the junction site between SMC-1 C lobe and the coiled-coil arm showed a series of phenotypes,including synapsis defects at pachytene,abnormal bivalent formation at diakinesis,elevated germ cell apoptosis,and high incidence of males among the progeny.In mutants with reduced hydrophobicity at the SMC-1 C terminus,no obvious reproductive defects were observed when the worms were young.However,a series of phenotypes were observed for the aged worms,including abnormal chromosome remodeling at diakinesis,reduced brood sizes,and increased male progeny.In summary,our study in C.elegans revealed that changes in SMC-1hydrophobicity can lead to meiosis defects and reproductive aging,providing a useful reference for the diagnosis,prevention and treatment of human reproductive diseases.