Mammalian reproductive tract mucins

Mucin glycoproteins are major constituents of the glycocalyx that covers mu cosal epithelium. Two broad classes of mucins exist: membrane-associated an d secretory. Of the secreted mucins, those crith cysteine-rich regions are thought to polymerize through disulphide bonds. Among these gel-forming muc ins are MUC2, MUC5AC, MUC5B and possibly MUC6. MUC7 lacks cysteine-rich dom ains and is thought to be secreted as a soluble monomer, Incomplete sequenc e information prevents classification of other mucins. Tandem repeats of am ino acids rich in serine, threonine and proline are a common element in muc in core proteins, giving rise to relatively rigid, linear molecules with gr eat potential for glycosylation. Ten distinct mucin genes have been identif ied in humans so far. Patterns of expression vary greatly. While MUC9, or o viductin, appears to be restricted to oviduct, the transmembrane mucin MUC1 is widely expressed. Proven functions for the different mucins are largely unknown, although potential functions are addressed in this review. Geneti c and protein sequence information and expression profiles are also summari zed, followed by a description of mucin assembly. Special attention is give n to mucin expression in male and female reproductive tracts.