Expression Patterns and Post-translational Modifications Associated with Mammalian Histone H3 Variants

Sandra B. Hake, Benjamin A. Garcia, Elizabeth M. Duncan, Monika Kauer, Graham Dellaire, Jeffrey Shabanowitz, David P. Bazett-Jones, C. David Allis, Donald F. Hunt
2005 Journal of Biological Chemistry  
Covalent histone modifications and the incorporation of histone variants bring about changes in chromatin structure that in turn alter gene expression. Interest in non-allelic histone variants has been renewed, in part because of recent work on H3 (and other) histone variants. However, only in mammals do three non-centromeric H3 variants (H3.1, H3.2, and H3.3) exist. Here, we show that mammalian cell lines can be separated into two different groups based on their expression of H3.1, H3.2, and
more » ... f H3.1, H3.2, and H3.3 at both mRNA and protein levels. Additionally, the ratio of these variants changes slightly during neuronal differentiation of murine ES cells. This difference in H3 variant expression between cell lines could not be explained by changes in growth rate, cell cycle stages, or chromosomal ploidy, but rather suggests other possibilities, such as changes in H3 variant incorporation during differentiation and tissue-or species-specific H3 variant expression. Moreover, quantitative mass spectrometry analysis of human H3.1, H3.2, and H3.3 showed modification differences between these three H3 variants, suggesting that they may have different biological functions. Specifically, H3.3 contains marks associated with transcriptionally active chromatin, whereas H3.2, in contrast, contains mostly silencing modifications that have been associated with facultative heterochromatin. Interestingly, H3.1 is enriched in both active and repressive marks, although the latter marks are different from those observed in H3.2. Although the biological significance as to why mammalian cells differentially employ three highly similar H3 variants remains unclear, our results underscore potential functional differences between them and reinforce the general view that H3.1 and H3.2 in mammalian cells should not be treated as equivalent proteins. Eukaryotic organisms depend on complex and highly regulated mechanisms to activate or silence genes in response to a variety of stimuli, including environmental changes, cell cycle regulators, and developmental cues. An increasing body of evidence suggests that epigenetic mechanisms involving chromatin remodeling alter the accessibility of proteins, such as transcription factors, to the DNA template. FIGURE 3. Analysis of histone H3 variant expression in different cell cycle phases. A, HeLa cells were synchronized in G 1 phase by a double thymidine block, released and analyzed every 2 h by FACS. B, quantification of FACS analysis results from the experiment shown in A. C, immunoblots with histones isolated from HeLa cells, described in A, using antibodies against H3 S28 phosphorylation (H3 S28P, top) and C-terminal tail of H3 (H3, bottom) as loading control. D, quantification of H3.3A and H3.3B (left) and H3.2, H3.1H, and H3.1L (right) Mammalian Histone H3 Variants
doi:10.1074/jbc.m509266200 pmid:16267050 fatcat:zwnwlhdm4nbalbf62xrictca4u