MET-2 and SET-25 have sexually dimorphic effects on chromosome structure in Caenorhabditis elegans
Date
2023
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Publisher
University of Delaware
Abstract
Meiosis is a highly conserved cellular division, which allows for the formation of haploid gametes. During meiosis chromosomes undergo two successive segregation events. Homologous chromosomes segregate in meiosis I and the sister chromatids subsequently segregate in meiosis II, leading to the production of egg and sperm with half the number of chromosomes of the parent cells. Although many similarities exist between meiosis in males and females, there are also meiotic mechanisms that differ between oogenesis and spermatogenesis. In C. elegans, we found that the bivalent length of diakinesis oocytes is significantly longer than spermatocytes. In addition, we found that mutations in different genes involved in histone post-translational modifications have distinct impacts on oocyte and spermatocyte bivalent length. A mutation of set-25, a histone methyltransferase converting histone H3 lysine 9 dimethylation (H3K9me2) to trimethylation (H3K9me3), reduces the bivalent length in oocytes. On the other hand, a mutation of met-2, a histone methyltransferase depositing H3K9me2 in the germ line decreases the bivalent length in spermatocytes. Although bivalent length is altered in these mutants, I discovered that there is no significant impact on embryonic viability. Because the epigenome is complex there could be redundant mechanisms to prevent germline dysfunction. Analysis of a met-2(n4256) set-25(n5021) double mutant, which have previously been found to interact genetically, resulted in a significant increase in diakinesis bivalent length compared to wild type and the single mutants. Through immunostaining against histone H3 lysine 9 dimethylation and trimethylation, we found robust localization of H3 lysine 9 trimethylation at diakinesis nuclei in both spermatogenesis and oogenesis, but H3 lysine 9 dimethylation is absent at diakinesis in both hermaphrodite and male germlines. Analysis of global gene transcription in spermatogenesis with an antibody against an active form of RNA polymerase II revealed that a delay in the silencing of global transcription occurs in met-2(n4256). These findings have revealed that two histone methyltransferases, MET-2 and SET-25, have differential roles on chromosome compaction and structure in C. elegans oogenesis and spermatogenesis.
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Keywords
Caenorhabditis elegans, Sexually dimorphic, Chromosome structure