Sperm nuclear proteome and its epigenetic potential

The main function of the sperm cell is to transmit the paternal genetic message and epigenetic information to the embryo. Importantly, the majority of the genes in the sperm chromatin are highly condensed by protamines, whereas genes potentially needed in the initial stages of development are associated with histones, representing a form of epigenetic marking. However, so far little attention has been devoted to other sperm chromatin-associated proteins that, in addition to histones and protamines, may also have an epigenetic role. Therefore, with the goal of contributing to cover this subject we have compiled, reviewed and report a list of 581 chromatin or nuclear proteins described in the human sperm cell. Furthermore, we have analysed their Gene Ontology Biological Process enriched terms and have grouped them into different functional categories. Remarkably, we show that 56% of the sperm nuclear proteins have a potential epigenetic activity, being involved in at least one of the following functions: chromosome organization, chromatin organization, protein-DNA complex assembly, DNA packaging, gene expression, transcription, chromatin modification and histone modification. In addition, we have also included and compared the sperm cell proteomes of different model species, demonstrating the existence of common trends in the chromatin composition in the mammalian mature male gamete. Taken together, our analyses suggest that the mammalian sperm cell delivers to the offspring a rich combination of histone variants, transcription factors, chromatin-associated and chromatin-modifying proteins which have the potential to encode and transmit an extremely complex epigenetic information.