CLONING OF RAT MUC5AC MUCIN GENE - COMPARISON OF ITS STRUCTURE AND TISSUE DISTRIBUTION TO THAT OF HUMAN AND MOUSE HOMOLOGS

The human mucin gene MUC5AC codes for a large mucin which has tandem r epeat units rind cysteine rich regions characteristic of several membe rs of this class of glycogroteins. Human epithelia expressing the muci n include that of stomach, bronchus/trachea, endocervix and conjunctiv a. We report here a 3.8 kb partial sequence of a rat homologue for the human MUC5AC gene and compare its tandem repeat sequence and cysteine rich domains to those of the human and mouse gene. Rat and mouse have the same number of amino acids (16) in their Muc5AC tandem repeat uni ts and share 69% sequence similarity, whereas human MUC5AC has only 8 amino acids in its tandem repeat. In rat, the tandem repeat domain is flanked at its 3' end by a non-repeat region coding for 1142 amino aci ds. Four cysteine rich subdomains were identified in this region; one of these has 64% similarity to a corresponding region in human MUC5AC and 80% similarity to a mouse MUC5AC cysteine rich region. Southern bl ot analysis revealed cross hybridization of a probe for the rat cystei ne rich region, to human, mouse, rabbit, and porcine genomic DNA; the rat tandem repeat probe hybridized with mouse and rabbit only. Unlike humans, rat expressed MUC5AC message detectable by Northern blot and i n situ hybridization only in stomach epithelium and conjunctival goble t cells. (C) 1997 Academic Press.