Studies On The Regulation Of Meiotic Progression By SKR-1

Meiosis is a specialized cell division process by which sexually reproducing diploid organisms,The halving of chromosome number is accomplished by following one round of DNA replication with two consecutive rounds of chromosome segregation.Meiotic prophase I is a prolonged process,and a series of unique events occurring during this period are critical for the correct separation of chromosomes,including homologous chromosome pairing,synapsis,crossover formation,chromosome remodeling,and condensation.The synaptonemal complex(SC)is a large protein complex assembled between paired homologous chromosomes in the meiotic prophase I,and its structure and organization are highly conserved among species.The most conserved function of the synaptonemal complex is to mediate homologous pairing and recombination,and promote the formation of interhomologous crossovers to facilitate the precise segregation of meiotic chromosomes.Caenorhabditis elegans is a powerful model organism for the study of meiosis.The germ cells in the gonads are arranged in a temporal and spatial gradient manner.All stages of meiotic prophase can be observed in a single gonad,providing excellent conditions for cell biology study of meiosis.The synaptonemal complex is a dynamic structure,and the regulatory mechanisms underlying the dynamic changes of the SC have been receiving much attention recently.Previous study in the laboratory conducted a series of immunoprecipitation and mass spectrometry analyses to identify the binding partners of some structural components of the SC.A series of SC-binding proteins were discovered,and they may act as SC regulators to control the polymerization and depolymerization of the SC.From SYP-2 immunoprecipitates,SKR-1 was identified as a novel SC-binding protein.Immunofluorescence analysis of the skr-1::gfp nematode obtained by the CRISPR-Cas9 gene editing method revealed that SKR-1::GFP was expressed in many tissues of the nematode,including gonads and embryos,suggesting that this protein is not a germline-specific protein.During meiotic prophase I,SKR-1::GFP localizes to the nucleus and colocalizes with the SC,confirming that the protein is a SC-binding protein.In syp-1 mutants,where the SC is missing,and the nuclear localization of SKR-1::GFP is perturbed,indicating that the SC is responsible for recruiting SKR-1::GFP to the meiotic chromosomes.Reproductive cycle analysis revealed that skr-1mutants has an extended reproductive cycle compared to wild type,and such extension was further confirmed in aged worms that were provided with young adult male sperms by hybridization.To investigate the mechanism by which skr-1mutations cause prolonged reproductive cycles,we further analyzed the effect of skr-1mutations on meiotic progression.Immunofluorescence staining and other analyses did not reveal obvious defects in the polymerization and depolymerization process of the SC in meiosis,suggesting that the prolongation of the reproductive cycle in skr-1mutants is not a result of changes in SC dynamic regulation.In addition,the deletion of skr-1 in syp-1 mutant background can also lead to an extension of the reproductive cycle,further suggesting that the effect of SKR-1 on the reproductive cycle is independent of the SC.The mechanism by which the skr-1 mutation extends the reproductive cycle of nematodes remains to be elucidated.SKR-1 is a key protein subunit of the E3 ubiquitin ligase SCF.We found that in skr-1::gfp transgenic nematodes,the SC could not assemble normally and form aggregates under high temperature culture condition(25 °C).SKR-1::GFP is also recruited to SC aggregates under high temperature conditions.These findings suggest that the ubiquitin-proteasome pathway may be involved in the SC assembly and dynamic regulation,and the insertion of the GFP tag may exert a dominant negative affect on ubiquitin-proteasome pathway,resulting in abnormal assembly of the SC.These findings have opened up new directions for futher studies.