Visualization of inactive X chromosome in preimplantation embryos utilizing MacroH2AEGFP transgenic mouse

One of the two X chromosomes is inactivated in female eutherian mammals. MacroH2A, an unusual histone variant, is known to accumulate on the inactive X chromosome (Xi) during early embryo development, and can thus be used as a marker of the Xi. In this study, we produced a transgenic mouse line expressing the mouse MacroH2A1.2enhanced green fluorescent protein (EGFP) fusion protein (MacroH2AEGFP) under the control of a CAG promoter and verified whether MacroH2AEGFP would be useful for tracing the process of X chromosome inactivation by visualizing Xi noninvasively in preimplantation embryos. In transgenic female mice, MacroH2AEGFP formed a fluorescent focus in nuclei throughout the body. In female blastocysts, the MacroH2AEGFP focus colocalized with Xist RNA, well known as a marker of Xi. Fluorescence marking of Xi was first observed in some embryonic cells between the 4- and 8-cell stages. These results demonstrate that MacroH2A can bind to the Xi by around the 8-cell stage in female mouse embryos. These MacroH2AEGFP transgenic mice might be useful to elucidate the process of X chromosome inactivation during the mouse life cycle. genesis 51:259267. (c) 2013 Wiley Periodicals, Inc.