DNA methylation of placenta-specific Cyp19 promoters of cattle and sheep.

Locally produced estrogens are important paracrine regulators of placental growth and differentiation in cattle and sheep. The key enzyme of estrogen biosynthesis, aromatase cytochrome P450, is encoded by CYP19. Transcription of this gene in fetal cotyledons is the first regulatory step of placental estrogen production. The aim of the present study was to comparatively investigate if epigenetic mechanisms as tissue- and differentiation-specific DNA methylation might be involved in the regulation of placental CYP19 expression. Earlier investigations demonstrated that cattle and sheep use different promoters, P1.1 and P1.5 for placental CYP19 expression, respectively. During the present investigation, methylation of individual CpG dinucleotides within these promoter regions was analyzed with bisulfite direct sequencing in placental and luteal tissue. Transcript abundance in sheep was determined with qPCR. Both promoters contain only few CpGs and can therefore be classified as "low CpG densitiy regions". The average methylation levels of both promoter regions were significantly reduced in cotyledons compared to caruncles and corpus luteum of both species, which inversely coincides with high and low expression levels, respectively. It was evident however that even neighbouring CpGs can show very different, individual methylation levels. From the data we conclude that (1) CYP19 promoters are differentially methylated in ovine and bovine placental tissues of foetal and maternal origin; (2) DNA methylation is suggestively involved in the regulation of CYP19 expression; (3) the DNA methylation status on its own is not sufficient for the selection of tissue-and species-specific CYP19 promoters.