Centrosomal association of histone macroH2A1.2 in embryonic stem cells andsomatic cells

The histone 2A variant macroH2A1.2 is expressed in female and male mammals and is implicated in X-chromosome inactivation and autosomal gene silencing . In undifferentiated and early differentiating murine embryonic stem (ES) cells a cytosolic pool of macroH2A1.2 has recently been reported and found to be associated with the centrosome. Here, we show that the centrosomal as sociation of macroH2AI.2 is a widespread phenomenon and is not restricted t o undifferentiated and early differentiating ES cells. By indirect immunofl uorescence we detect macroH2A1.2 protein in a juxtanuclear structure that d uplicates once per cell cycle and colocalizes with centrosomal gamma -tubul in in both XX and XY ES cells prior to and throughout their differentiation . MacroH2A1.2 localization to the centrosome is also observed in female and male somatic cells, both in interphase and in mitosis. Biochemical analysi s demonstrates that the association between macroH2A1.2 and the centrosome in somatic cells is stable, as macroH2A1.2 copurifies with centrosomes isol ated from human lymphoblasts. Therefore, in addition to a nuclear pool of m acroH2A1.2 a fraction of the histone is associated with the centrosome in v arious cell types and throughout ES cell differentiation. (C) 2001 Academic Press.