Chromatin topology during the transformation of the mouse sperm nucleus into pronucleus in vivo.

Time relationships of sperm chromatin dispersion and sperm nucleoprotein replacement have been studied in vivo, by an in situ cytochemical approach. We used the Feulgen reaction to reveal DNA, which allow us to record both processes simultaneously, on the basis of the return after fertilization to haploid Feulgen values after sperm nucleoprotein replacement with somatic histones. We have shown that sperm nucleoprotein replacement occurs at around anaphase II, whereas sperm chromatin dispersion is massive between the anaphase and telophase II oocyte phases. The morphological pattern of sperm chromatin dispersion supports the idea that the process involves the whole sperm chromatin mass simultaneously, with the region located between the implantation fossa and the postacrosomial region the last to swell.