DNA methylation and chromatin accessibility of the proximal Cyp19 promoter region 1.5/2 correlate with expression levels in sheep placentomes

Placental oestrogens play an important role as local regulators of placental growth and differentiation during gestation, and toward term they are also involved in the preparation of parturition. They are synthesized within the fetal cotyledons of placentomes by aromatase cytochrome P450 (P450arom; EC 1.14.14.1), the product of the Cyp19 gene. The first step of regulation of P450arom expression, and hence enzyme activity and oestrogen production, takes place at the level of Cyp19 transcription, which is driven by a proximal promoter region, P1.5/2, in the sheep placenta. The aim of the present study was to find out if different Cyp19 expression levels, which previously had been observed in ovine placentome tissues, correlate with the tissue-specific chromatin structure of the promoter. To this end, we investigated the chromatin structure across the P1.5/2 region in caruncles and cotyledons from 100 and 125 days pregnant ewes, and in term placentae, respectively, by analyzing the DNA methylation and the accessibility to restriction digestion. Our data show that: (1) cotyledonal DNA was significantly lower methylated than caruncular DNA; (2) methylation of cotyledonal DNA was low at 100 and 125 days of pregnancy, and increased to a significant higher level in term placentae; and (3) concurrently, cotyledonal chromatin became inaccessible to restriction digestion at term of gestation. The results imply that DNA methylation and chromatin accessibility of the P1.5/2 promoter region correlate with expression levels of the Cyp19 gene.