Genetic Polymorphism of the Epithellal Mucin, PAS-I, in Milk Samples from the Major Dairy Breeds

¹ Department of Neurosciences, Center for Molecular Genetics, 0634J University of California San Diego La Jolla 92093
² Department of Diary and Animal Science, The Pennsylvania State University, University Park 16802

Genetic polymorphism in a mucin of the human milk fat globule arises from variable numbers of a tandemly repeated amino acid sequence. As a consequence, the gene from each parent expresses a variable-sized protein. This is manifest on SDS gels in the form of either one or, more often, two protein bands, which differ among individuals in mobility. Evidence of such polymorphism in the bovine mucin, PAS-I, was first obtained from Holstein milk samples.

The objective of this study was to evaluate the other major dairy breeds for polymorphism of their PAS-I. Milk samples from individual Jerseys, Guernseys, Ayrshires, and Brown Swiss were analyzed by SDS-PAGE. Bands of the mucin varying in number and mobility were seen in samples from all four breeds. In three of the breeds (Ayrshire, Brown Swiss, and Jersey), there was evidence that two alleles for PAS-I may have become predominant, possibly through de-generation in the structure of their tandem repeats, one that gives rise to a faster moving mucin (relative molecular weight 170,000) and the other to a slower form (relative molecular weight 200,000). In contrast, the PAS-I band patterns on SDS gels for both Guemseys and Holsteins were characterized in nearly 50% of samples by two close bands near the 205,000-molecular weight marker. This pattern was never seen in the other three breeds. The findings suggest a genetic kinship among the Ayrshire, Brown Swiss, and Jersey, on the one hand, and between the Holstein and Guemsey, on the other.

Key Words: polymorphism • mucin • PAS-I • membrane • milk fat globule

Submitted on August 26, 1991
Accepted on October 31, 1991

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