Regulation Of Synaptonemal Complex Dynamics By Ubiquitination Pathway Related Proteins

Meiosis is a special form of cell division necessary for sexual reproduction.It is the process of producing haploid gametes(sperm and eggs)from a diploid germ cell.In this process,DNA is duplicated only once,while chromosomes are separated twice.A ccurate meiotic chromosome segregation depends on the orderly occurrence of several key events in the prophase,including homologous pairing,synaptonemal complex(SC)formation,programmed DNA double-strand break formation,and the formation of genetic crossover.The SC is a large,structurally highly conserved ladderlike protein complex formed between homologous chromosomes after homologous pairing.SC promotes homologous recombination and crossover formation between homologous chromosomes,thus ensuring the correct segregation of homologous chromosomes and the genetic diversity of progeny.SC is not a static structure,it undergoes a dynamic process of assembly,maintenance and disassembly during the meiotic prophase.The dynamic process from assembly to disassembly of the synaptonemal complex needs to be precisely regulated to ensure the proper meiotic progression.Known protein modifications,such as Nterminal acetylation,SUMO modification,and phosphorylation,play important roles in regulating the dynamics of the SC during meiosis in different organisms.In this study,we focused on the role of ubiquitination on SC dynamics.Using model organism Caenorhabditis elegans,we performed immunoprecipitation and mass spectrometry analysis of central element of the SC to identify SC binding proteins.Three proteins related to the ubiquitination pathway were identified in the immunoprecipitation of SC central element SYP-2,all of which belong to the E3 ubiquitin ligase,including Skp-1-related genes,skr-1 and skr-2,and B0281.3.With immunofluorescence microscopy analysis of gonads dissected from skr-1::gfp strain,we confirmed that SKR-1:: GFP indeed co-located with SC during meiotic prophase,implying that the ubiquitination pathway related proteins discovered by proteomic analysis may play a key SC regulatory role during meiosis.In single mutants of skr-1,skr-2 and B0281.3,the SC was fully assembled along the length of the chromosome,suggesting that these gene related ubiquitination pathways may not be necessary for SC assembly.By measuring the fluorescence intensities of SC components in the germline,we found that these gene related ubiquitination pathways could affect the amount of SC polymerization on the chromosomes.Under high temperature culture condition,proper morphologic maintenance of the SC was disrupted in these ubiquitination mutants,and polycomplex was formed,indicating that ubiquitination modification is crucial for heat resistance of the SC.Moreover,our data further suggested that the recovery of high-temperature induced SC aggregates under the normal temperature culture condition also depended on ubiquitination modification.These data thus suggest that although ubiquitination modification is not necessary for SC assembly between homologous chromosomes,it is essential for the dynamic property of the SC.By analyzing offspring survival rates of the ubiquitination-related mutants after heat exposure,we found that the mutations of these genes resulted in a decrease of the offspring survival rate compared to the wild type,suggesting that ubiquitination-regulated SC dynamic property may be an important mechanism for the temperature adaptation in nematodes.These findings may provide useful references for the diagnosis and prevention of human reproductive health problems.