Repressive and active histone methylation mark distinct promoters in human and mouse spermatozoa (Nimblegen)

In higher eukaryotes, histone methylation is involved in the maintenance of cellular identity during somatic development. During spermatogenesis, most nucleosomes are replaced by protamines. Therefore, it is unclear if histone modifications function in paternal transmission of epigenetic information. Here we show that active H3K4 di-methylation (H3K4me2) and repressive H3K27 tri-methylation (H3K27me3), two modifications important for Trithorax and Polycomb-mediated gene regulation, are present in chromatin of human spermatozoa and show methylation-specific distributions at regulatory regions. H3K4me2-marked promoters control gene functions in spermatogenesis and cellular homeostasis suggesting that this mark reflects germline transcription. In contrast, H3K27me3 marks promoters of key developmental regulators in sperm as in soma. Many H3K27me3-marked genes are never expressed in the male and female germline, and in early “totipotent” embryos, suggesting a function for Polycomb in repressing somatic determinants across generations. Targets of H3K4me2 and H3K27me3 are also modified in mouse spermatozoa, implicating an evolutionary conserved role for histone methylation in chromatin inheritance via the male germline.