Immunocytochemical localization of histones H2B, H3 and H4 in pronuclei and four-cell stages of porcine embryos. Preliminary results.

In this preliminary work, using pig embryos ultrastructural immunocytochemistry with polyclonal antibodies against purified histones was used to demonstrate both their localization and the time of their appearance in pronuclei, from 15 h after ovulation (pronuclear stage) to 48 h postinsemination (4-cell stage). In pronuclei, the histones H2B, H3, and H4 were located in the heterochromatin as soon as it appeared. Usually, one of the pronuclei seemed to be more heavily labelled. The chromatin facing the zone of pronuclear contact formed a bowl-shaped region in each pronucleus heavily labelled for these histones. The so-called pseudo-nucleoli were present in both pronuclei and contained H2B. In 4-cell stages, the labelling intensities of heterochromatin for H2B, H3 and H4 were equal in all the nuclei. H2B was still evident in the pseudo-nucleoli, but in a lower quantity than before. The condensed chromatin located either under the nuclear envelope or surrounding the pseudo-nucleoli was heavily labelled for H2B, H3 and H4.