Analysis of global and gene-specific acetylation of histones in the liver of American bullfrog (Rana catesbeiana) tadpoles acclimated to low temperature.

Abstract

Severe environmental stressors such as low temperatures can affect gene expression by changing epigenetic states. American bullfrog (Rana catesbeiana) can overwinter as tadpoles, which can be active even in winter. However, the molecular mechanisms of epigenetic controls by which the tadpoles acclimate to low temperature are still unclear. In this study, we aimed to clarify the molecular mechanisms of global and gene-specific epigenetic regulations of low-temperature acclimation. We found that the global acetylation was decreased in the liver of bullfrog tadpoles acclimated to low temperature. The amounts of transcripts for two histone acetyltransferases were higher in the liver of tadpoles acclimated to low temperature than in those acclimated to warm temperature, while we observed no significant differences in the amounts of transcripts for histone deacetylases. We also found that the amounts of transcripts and acetylated histones on the specific temperature-responsive genes scd and cyp7a1 whose transcripts were increased and decreased, respectively, in response to low temperature were positively correlated. Cellular acetyl-CoA levels were higher in the liver of tadpoles acclimated to low temperature than in those acclimated to warm temperature. These results contradicted the states of histone acetylation, suggesting that bullfrog tadpoles have different epigenetic mechanisms to modify the histones when compared with those of other organisms such as reptiles and mammals, even though the relationship between the transcript amount and the states of histone acetylation on temperature-responsive genes was similar to that of mammals.