Histone macroH2A1 is concentrated in the inactive X chromosome of female preimplantation mouse embryos.
MacroH2As are core histone proteins with a hybrid structure consisting of a domain that closely resembles a full-length histone H2A followed by a large nonhistone domain. We recently showed that one of the macroH2A subtypes, macroH2A1.2, is concentrated in the inactive X chromosome in adult female mammals. Here we examine the timing of the association of macroH2A1.2 with the inactive X chromosome during preimplantation mouse development in order to assess the possibility that macroH2A1 participates in the initiation of X inactivation. The association of macroH2A1.2 with one of the X chromosomes was observed in 50% of blastocysts, occurring mostly, if not exclusively, in extraembryonic cells as was expected from previous studies, which indicated that X inactivation in embryonic lineages happens after implantation. Examination of earlier embryonic stages indicates that the association of macroH2A1 with the inactive X chromosome begins between the 8- and 16-cell stages. Of the changes that are known to happen during X inactivation in preimplantation embryos, the accumulation of macroH2A1 appears to be the earliest marker of the inactive X chromosome and is the only change that has been shown to occur during the period when transcriptional silencing is initiated.
Costanzi
C
C
Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
Stein
P
P
Worrad
D M
DM
Schultz
R M
RM
Pehrson
J R
JR
D000818:Animals; D000918:Antibody Specificity; D001755:Blastocyst / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism; D004303:Dosage Compensation, Genetic; D047108:Embryonic Development / Q000502:physiology*; D005260:Female; D006657:Histones / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D051379:Mice; D011247:Pregnancy; D013997:Time Factors; D014960:X Chromosome / Q000378:metabolism*
D002843:Chromatin; D006657:Histones; C120756:macroH2A histone