Histone MacroH2A1.2 is concentrated in the XY-body by the early pachytene stage of spermatogenesis

The pairing of sex chromosomes during meiosis in male mammals is associated with ongoing heterochromatinization and X inactivation. This process occur s in a specific area of the nucleus that can be discerned morphologically: the sex vesicle or XY-body. In contrast to X inactivation in the somatic ce lls of female mammals the reasons for X inactivation in the male germline r emain obscure. We have recently demonstrated that the inactive X chromosome in somatic cells of female mammals is marked by a high concentration of hi stone macroH2A. Here we investigate X inactivation in the meiotic cells of the male germline. We demonstrate here that macroH2A1.2 is present in the n uclei of germ cells starting first with localization that is largely, if no t exclusively, to the developing XY-body in early pachytene spermatocytes, Our results suggest that inactivation of sex chromosomes in the male germ c ell includes a major alteration of the nucleosomal structure. (C) 2000 Acad emic Press.