Methylation of progesterone receptor isoform A and B promoters in the reproductive system of cows.

The aim of this study was to investigate whether the promoters of progesterone receptor isoform A (PGRA) and B (PGRB) are methylated and to determine the percentage of methylation occurring for each isoform. Genomic DNA was isolated from the corpora lutea (CL) and endometrial slices from cows on Days 2-5, 6-10, 11-16 and 17-20 of the oestrous cycle. DNA was bisulphite-converted and amplified using methyl-specific polymerase chain reaction (PCR) with primers that detect both methylated and unmethylated sequences. The determination of the percentage of the methylation was performed using HpaII and MspI restriction enzymes. Methyl-specific PCR showed partial methylation of PGRA and PGRB promoters in the CL and endometrium during the oestrous cycle. Methylation for PGRA was between 15 and 17% and for PGRB was in the range of 6 to 7.7% during the oestrous cycle in the CL. In the endometrium, the methylation for PGRA was between 6 and 7.3% and for PGRB was between 3 and 4.8% during the oestrous cycle. The data obtained indicate that the higher promoter methylation of the PGRA isoform could be a mechanism for regulation of PGRA inhibitory activity against PGRB and, in this way, methylation may influence the regulation of progesterone action in the CL and endometrium.