The polymorphic epithelial mucin MUC1 in human endometrium is regulated with maximal expression in the implantation phase

After ovulation, progesterone stimulates a temporally regulated secretory transformation in human endometrial epithelium. Using a combination of immunohistochemistry, and Western and Northern blotting, we demonstrate that 1) the polymorphic epithelial mucin MUC1 is secreted by human endometrial epithelium; 2) low levels of both mRNA and core protein are present in the preovulatory phase of the menstrual cycle; 3) mRNA levels increase several- fold after ovulation, consistent with transcriptional regulation by progesterone; 4) there is an increase in translation product in postovulatory endometrium; and 5) the tandem repeat domain of the MUC-1 polypeptide is glycosylated in endometrium.