Sialomucin complex (Muc4) expression in the rat female reproductive tract

Previous studies in our laboratory demonstrated the presence of sialomucin complex (SMC)/Muc4 covering the rat uterine luminal epithelium. SMC/Muc4 ex pression in the uterus is regulated by estrogen and progesterone and lost a t the time of receptivity. In contrast to this hormonal regulation at the u terine luminal surface, SMC/Muc4 in the uterine glandular epithelium, ovidu ct, cervix, and vagina was constitutively expressed at all stages of the es trous cycle, Furthermore, SMC was expressed in the cervix and vagina of the ovariectomized rat, even though it is not found in the uterine luminal epi thelium. Both soluble and membrane-hound forms of SMC were present in these tissues. Immunohistochemical analyses showed distinctive localization patt erns of SMC in the various tissues during the estrous cycle. Moreover, the previously unreported expression of SMC/Muc4 in the isthmus, ampulla, and i nfundibulum of the oviduct suggests potential functions in gamete developme nt, these results indicate that SMC/Muc4 is expressed in most tissues of th e female reproductive tract, in which it may have multiple functions. Howev er, hormonal regulation appears to be restricted to the uterine luminal epi thelium.