Polymorphic forms of the epithelial mucin, PAS-I (MUC1), in milk of Holstein cows (Bos taurus)

The polymorphic epithelial mucin, PAS-I (also known as MUC1), in individual milk samples from 119 Holstein cows was resolved into bands on SDS-gels. Mobility indices established for these bands provided evidence of four and possibly five polymorphic forms. Sialic acid, a major component of the oligosaccharide portion of PAS-I, was removed from the mucin by treatment of milk samples with neurominidase. This reduced the mobility of the mucin bands but did not alter their mobility relationships within a sample or among samples. Consideration of evidence from this and other studies indicates that the four or five polymorphic forms correspond to alleles, which are inherited, one each from sire and dam, and co-dominantly expressed. It appears that the Holstein population may carry several more alleles for PAS-I than do Ayrshire, Jersey or Brown Swiss cattle. In addition to these breed differences, some remarkable molecular differences have been noted between MUC1 (PAS-I) of human and mouse suggesting that research regarding molecular evolution of this mucin could provide another approach to understanding relationships among species.