Comparative analysis of expression of histone H2a genes in mouse

Abstract

Background: At least 18 replication-dependent histone H2a genes are distributed in 3 Hist gene clusters on different chromosomes of the mouse genome. In this analysis we designed specific PCR primers for each histone H2a transcript and studied the expression levels and patterns using quantitative RT-PCR (qRT-PCR). In addition, we compared histone H3 K9 acetylation levels in the promoter regions of H2a genes by ChIP (chromatin immunoprecipitation)--quantitative PCR (qPCR) analysis.

Results: RT-PCR analysis indicated that all 20 histone H2a genes assessed in this study are expressed. The replication-dependent histone H2a genes have different expression levels but similar expression patterns. Among the 20 histone H2a genes, the expression-level of H2afz, a replication-independent gene, was highest, and that of Hist1h2aa, a replication-dependent gene, was lowest. Among 18 replication-dependent H2a genes, the expression level of Hist3h2a was highest. The ChIP-qPCR analysis showed that histone H3 K9 acetylation levels in promoter regions of both H2afz and Hist3h2a are clearly higher than that in the promoter region of Hist1h2aa. The H3 K9 acetylation level in the promoter of Hist1h2aa is similar to that in the gamma-satellite region.

Conclusion: These results strongly suggest that histone H3 K9 acetylation plays a role in the expression of histone genes.

Figure 1

RT-PCR products. Lanes 1 and 19, DNA ladder marker; 2, Hist1h2aa transcript; 3, Hist1h2ab transcript; 4, Hist1h2ac transcript; 5, Hist1h2ad/1h2ao transcripts; 6, Hist1h2ae transcript; 7, Hist1h2af transcript; 8, Hist1h2ag transcript; 9, Hist1h2ah transcript; 10, Hist1h2ai/1h2aj transcripts; 11, Hist1h2ak transcript; 12, Hist1h2an transcript; 13, Hist2h2aa1/2h2aa2 transcripts; 14, Hist2h2ab/2h2ac transcripts; 15, Hist3h2a transcript; 16, H2afj transcript [9]; 17, H2afx transcript; 18, H2afz transcript.

Figure 2

Expression patterns and levels: results of a) first and b) second qRT-PCR analyses. X-axis, time (hours); Y-axis, expression level relative to H2afz expression level adjusted to 1.0 at 0 h in each experiment.

Figure 3

Sum of expression levels at 0, 1, 2, 3, 4, 5, and 6 h (S-phase) in Fig. 2. Blue and red indicate a) and b) in Fig. 2, respectively. Y-axis, sum of expression levels.