Weak but Uniform Enrichment of the Histone Variant macroH2A1 along the Inactive X Chromosome

Abstract

We studied the enrichment and distribution of the histone variant mH2A1 in the condensed inactive X (Xi) chromosome. By using highly specific antibodies against mH2A1 and stable HEK 293 cell lines expressing either green fluorescent protein (GFP)-mH2A1 or GFP-H2A, we found that the Xi chromosome contains ϳ1.5-fold more mH2A1 than the autosomes. To determine the in vivo distribution of mH2A1 along the X chromosome, we used a native chromatin immunoprecipitation-on-chip technique. DNA isolated from mH2A1-immunoprecipitated nucleosomes from either male or female mouse liver were hybridized to tiling microarrays covering 5 kb around most promoters or the entire X chromosome. The data show that mH2A1 is uniformly distributed across the entire Xi chromosome. Interestingly, a stronger mH2A1 enrichment along the pseudoautosomal X chromosome region was observed in both sexes. Our results indicate a potential role for macroH2A in large-scale chromosome structure and genome stability.

The Trithorax group protein Ash2l and Saf-A are recruited to the inactive X chromosome at the onset of stable X inactivation

“…Detection of macroH2A was less efficient and at the final time point we detected clear macroH2A foci in only 30% of the cells, compared with over 70% for Ash2l. This could be due to a less prominent enrichment of macroH2A on the Xi over the nuclear average (Mietton et al, 2009). The number of cells showing macroH2A enrichment increased with slower kinetics than did that of Saf-A and Ash2l, and reached a maximum between days 4 and 8 (Fig.…”

“…PcG proteins have been implicated in the maintenance of X inactivation in keeping with their well-established function in maintaining repression of developmental control genes (Wang et al, 2001). Factors that contribute to maintaining the silent state of the Xi further include the histone variant macroH2A (Costanzi and Pehrson, 1998;Mermoud et al, 1999;Mietton et al, 2009;Rasmussen et al, 2000), histone H4 hypoacetylation (Keohane et al, 1996) and DNA methylation (Sado et al, 2000;Sado et al, 2004). Recently, it has been shown that the Smchd1 protein is required for the maintenance of DNA methylation patterns and gene repression on the Xi (Blewitt et al, 2008).…”

The histone variant macroH2A1 marks repressed autosomal chromatin, but protects a subset of its target genes from silencing

“…MacroH2A1 is enriched on the inactive X chromosome (Xi) in mammals, and has been postulated to play an important, but unknown, role in the repression of gene expression associated with X inactivation (Ladurner 2003). Importantly, macroH2A1 has also been found in a variety of contexts on autosomes (Zhang et al 2005;Agelopoulos and Thanos 2006;Changolkar and Pehrson 2006;Choo et al 2006;Buschbeck et al 2009;Mietton et al 2009). Although recent studies have suggested a role for macroH2A1 in autosomal gene regulation (Zhang et al 2005;Agelopoulos and Thanos 2006;Changolkar and Pehrson 2006;Choo et al 2006;Changolkar et al 2007Changolkar et al , 2008Bernstein et al 2008;Buschbeck et al 2009), many questions about the role of macroH2A1 in the regulation of autosomal genes remain.…”

Current view of the potential roles of proteins enriched on the inactive X chromosome

“…E-mail: tsado@nara.kindai.ac.jp macroH2A2 is encoded by H2afy2. These are enriched on Xi in a chromosome-wide fashion and form a macro chromatin body (Chadwick and Willard, 2001;Costanzi and Pehrson, 2001;Mietton et al, 2009). Their recruitment occurs at the morula stage during mouse development (Costanzi et al, 2000), and at a relatively late phase in the process of X-inactivation during embryonic stem (ES) cell differentiation (Mermoud et al, 1999;Pullirsch et al, 2010).…”