Tissue-specific promoter methylation and histone modification regulate CYP19 gene expression during folliculogenesis and luteinization in buffalo ovary

Abstract

Aromatase, the key enzyme of estrogen biosynthesis, is encoded by the CYP19 gene. The expression of CYP19 gene is regulated in species- and tissue-specific manner by alternate use of different promoters. We have previously, cloned and characterized the tissue-specific promoter and tissue-specific transcripts in preovulatory (granulosa cells) and postovulatory (corpus luteum) structure of buffalo ovary. The present study was aimed to understand if epigenetic gene regulation through DNA methylation and histone modifications is involved in tissue-specific CYP19 gene regulation during folliculogenesis and luteinization in buffalo ovary. Methylation analysis of five CpG dinucleotides of ovary specific proximal promoter II showed hypo-methylation in large follicle while hyper-methylation in corpus luteum. However, PI.1, the exclusive promoter responsible for residual CYP19 gene expression in corpus luteum, was found to be hypermethylated. Analysis of histone modifications using ChIP assay revealed that the distal promoter (PI.1) of CYP19 gene is ∼40-fold more enriched with acetylated Histone H3 in corpus luteum than in the large follicle. This indicates that PI.1 chromatin was more accessible for transcription in corpus luteum as compared to large follicles. The chromatin accessibility for the proximal promoter (PII) in the preovulatory stage tends to be higher than the luteal tissue. However, the difference was not found to be significant. In vitro experiments showed the similar results. In conclusion, results of the present study suggests that tissue-specific methylation status of PII and chromatin remodeling through histone modifications of PI.1, coincides with the changes in expression of CYP19 gene and thus are the regulatory mechanism controlling its tissue-specific expression and promoter activity during folliculogenesis and luteinization.