Paternal histone H2A variant incorporation and function before and after fertilization in C. elegans [ChIP-seq]
During spermatogenesis, chromatin repackaging transforms germ cells into sperm and transmits paternal epigenetic information to embryos. We have found distinct functions in these processes for two C. elegans H2A variants, HTAS-1, a sperm-specific paralog, and HTZ-1, a conserved H2A.Z homolog. HTAS-1 activates and represses gene expression less than two-fold, indicating HTAS-1 does not globally silence genes. In contrast, during spermatogenesis HTZ-1 regulates different germline genes compared to HTAS-1. During oogenesis, HTZ-1 strongly represses sperm gene expression over six-fold and activates oocyte and sex-independent genes, revealing tissue-specific modes of HTZ-1 regulation. ChIP-seq analysis of sperm chromatin shows HTZ-1 is present in 75% of HTAS-1 targets. HTZ-1 is incorporated at promoters of targets not occupied by HTAS-1 but is depleted in promoters of genes also occupied by HTAS-1. Instead HTAS-1 and HTZ-1 incorporate within gene bodies of shared targets. Post- fertilization, paternally-contributed HTAS-1 regulates the expression of a large number of genes in mixed-staged embryos. Correspondingly, loss of HTAS-1 causes decreased fertility and delayed development. Our studies indicate H2A variants have distinct incorporation mechanisms during sperm formation and tissue-specific functions in gene expression and fertility. Overall design: Chromatin immunoprecipitation DNA-sequencing (ChIP-seq) for histone variants HTZ-1 and HTAS-1 was performed in C. elegans sperm.