Epigenetic analysis of human spermatozoa after their injection into ovulated mouse oocytes

BACKGROUND: The epigenetic status of human spermatozoa is difficult to analyse. The method of interspecies fertilization can be used for different purposes. The aim of our work was to adopt this approach for the detailed analysis of epigenetic status of human spermatozoa injected into mouse oocytes. METHODS: Human spermatozoa were injected into ovulated mouse oocytes. When both parental pronuclei were formed, the zygotes were fixed and labeled with antibodies against histones methylated or acetylated at different positions (residues). RESULTS: Our results show that human spermatozoa injected into mouse oocytes fully respond to oocyte cytoplasmic factors and form analysable pronuclei. The labeling of zygotes showed that as in other species, the paternal chromatin is extensively epigenetically remodeled. CONCLUSIONS: The interspecies ICSI may be a powerful tool for the analysis of sperm epigenetic status even with a very low number of spermatozoa available. This analysis could be used as an additional approach for the assessment of certain forms of human infertility, as well as for testing the normality of male gametes obtained from embryonic stem cells.