Gastrointestinal expression and partial cDNA cloning of murine Muc2

To help us investigate the role of mucin in the protection of the colonic e pithelium in the mouse, we aimed to identify the murine colonic mucin (MCM) and its encoding gene. We isolated MCM, raised an anti-MCM antiserum, and studied the biosynthesis of MCM in the gastrointestinal tract. Isolated MCM resembled other mucins in physicochemical properties. Anti-MCM recognized MCM as well as rat and human MUC2 on Western blots, interacting primarily w ith peptide epitopes, indicating that MCM was identical to murine Muc2. Usi ng anti-MCM and previously characterized anti-human and anti-rat MUGS antib odies, we identified a murine Muc2 precursor in the colon of similar to 600 kDa, which appeared similar in size to rat and human MUC2 precursors. West ern blotting, immunoprecipitation of metabolically labeled mucins, and immu nohistochemistry showed that murine Muc2 was expressed in the colon and the small intestine but was absent in the stomach. To independently identify m urine Muc2, we cloned a cDNA fragment from murine colonic mRNA, encoding th e 302 NH2-terminal amino acids of murine Muc2. The NH2 terminus of murine M uc2 showed 86 and 75% identity to the corresponding rat and human MUC2 pept ide sequences, respectively. Northern blotting with a murine Muc2 cDNA prob e showed hybridization to a very large mRNA, which was expressed highly in the colon and to some extend in the small intestine but was absent in the s tomach. In situ hybridization showed that the murine Muc2 mRNA was confined to intestinal goblet cells. In conclusion, by two independent sets of expe riments we identified murine Muc2, which appears homologous to rat and huma n MUC2. Because Muc2 is prominently expressed in the colon, it is most like ly to be the predominant mucin in the colonic mucus layer.