Histone H3Acetylation And Lysine9Trimethylation Are Involved In The Epigenetic Regulation Of Slow Skeletal Troponin I Expression During Heart Development

Objective：Two main troponin I genes, cardiac (cTnI) and slow skeletal(ssTnI), are expressed in the mammalian heart under the control of adevelopmentally regulated program. ssTnI is expressed first in embryonicand fetal heart, and is then downregulated by unknown mechanisms afterbirth. In our previous studies we have demonstrated that ssTnI expression inthe heart is partially regulated by hormones, such as thyroid hormone, duringheart development. In the present study, we have explored the role of histonemodification in the regulation of ssTnI expression.Method： Mouse hearts were collected at different time of heartdevelopment, i.e. embryonic day15.5, postnatal day1, day7, day14and day21. Levels of histone H3acetylation (acH3) and histone H3lysine9trimethylation (H3K9me3) were detected using chromatinimmunoprecipitation (ChIP) assays in SURE domain (TnI slow upstreamregulatory element),300bp proximal upstream domain and the first intron ofssTnI gene, which are recognized as critical regions for ssTnI regulation. The expression of ssTnI mRNA was quantified using real time RT-PCRanalysis.Result：The levels of acetylation in histone H3that binds with SUREregion of ssTnI gene in the heart were decreased with the time duringdevelopment. However, the levels of trimethylation of histone H3lysine9site that binds with the same domain of ssTnI gene were not significantlychanged with time during development, showing two different tendencies inthe heart during the development. The levels of histone acetylation andmethylation on the sites that bind with the first intron of ssTnI gene showed adifferent pattern in the heart during the development. The levels of acH3thatbinds with the first intron did not show any significant changes in the heartduring the development. However, the levels of trimethylation on histoneH3lysine9site that binds to the first intron were slowly increased in theheart during the development, showing a different pattern compared to thehistone modification that occurs on SURE domain. Neither the acetylationlevels nor the methylation levels of histone H3that binds with the300bpupstream part of ssTnI gene had any changes in the heart during thedevelopment.Conculusion：Our results indicate that both histone acetylation andmethylation are involved in the epigenetic regulation of ssTnI expression inthe heart during the development, however, different histone modifications occur at different domains of ssTnI gene.