Mucins of the human endocervix

The physical character and amount of mucus secreted by the endocervix chang es dramatically at midcycle to facilitate the reproductive process. Mucins expressed by the endocervical epithelium contribute to this all-important p hysiologic event. This review summarizes work from our laboratory demonstra ting the mucin gene expression profile of cervical epithelium and mucin lev els in cervical mucus through the menstrual cycle. mRNA levels of the gel-f orming mucin MUC5B, the major gel-forming mucin expressed by the endocervic al epithelium, peak before midcycle and the amount of MUC5B protein per uni t total protein in cervical mucus peaks at midcycle. Message levels for MUC 4, a major membrane-spanning mucin of the endocervix, peak at midcycle, but protein levels of MUC4 in human cervical mucus have not been measured. Mes sage for each mucin diminishes dramatically as progesterone levels increase in the blood. These data suggest hormonal regulation of the two mucin gene s in the endocervix, but there is no information on their regulation at the biosynthetic level via genomic hormone response elements. Perhaps, through its hydrophilicity, the MUC5B mucin holds water in place a t the endocervical canal surface at midcycle, keeping the canal patent for sperm motility. A second potential role of the increased mucins at midcycle is to protect the cervix and uterus at the time when increased water is se creted into the cervical canal to facilitate sperm penetrance. Pathogens an d other seminal fluid components may be excluded from entering the uterus b y mucin trapping. Studies to determine the mechanism of hormonal regulation of mucins as well as the function of individual mucins are needed.