A review of epithelial muc1n genes and gene products

Mucin glycoproteins are the major ni; cromolecular components of the mucus thai covers the lumenal surfaces of cpithe ial organs and serves as a selective physical barrier between the extracellular milie i and the plasma membrane and cell interior. Mucins constitute îfamily of large highly glycosylated macromolecules that impart physical (aggregation, viscosit '. viscoelasticity. lubrication) and biological (protection) properties to mucus. MIR ins are highly glycosylated. with 50 to 90% of the molecular mass due to O-linkeii oligosaccharides. This carbohydrate serves to keep the protein core greatly exttnded and rod-like and ii likely key to the function. Mucins have been classif ed as secretory or membrane-associated. Secretory mucins constitute the "iscous mucus of the tracheobronchia], gastrointestinal, and reproductive facts and typically form extremely large oligomers through linkage of protein n onomers via disulfide bonds. The membrane associated mucins have a hydrophobl : membrane-spanning domain and have not been observed 10 form oligomeric coriplexes. In recent years cDNA and genomic clones have been obtained for nine hur lan mucin (MUC) genes, ( )nly three rnucins. MUC1. MUC2. and MUC7 have been completely sequenced. Characteristic features include tandem repeats, whicl are the regions of O-glycosy lation. Secreted mucins also contain cysteine-rich dorr ains that are homologous to each other. The cysteine-rich domains are responsible for the dimerization and oligomerization of the secreted mucins. Features of the g mes and gene products, expression patterns, and regulation will be discussed.