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β2-Microglobulin (β2M) forms the invariant chain of major histocompatibility complex (MHC) class I molecules and is essential for their structural stability and optimal functioning (Pedersen and others 1994). Loss or downregulation of MHC class I expression has been reported in various types of cancer (Chang and others 2003, Aptsiauri and others 2007). In human beings, mutations in β2M are a significant mechanism for the total loss of MHC class I, and β2M mutations have been described in colon carcinomas, melanomas and lymphomas. The mutational hot spot in β2M mutations is exon 1 (Garrido and others 1997, Pérez and others 1999), although no such mutations have been identified in breast cancers (Chen and others 1996). Several point mutations have been identified in β2M in healthy domestic dogs, and the data have been deposited in the Broad Institute Dog Genome Project database (CanFam2.0—2,544,508 SNPs; http://www.broadinstitute.org/mammals/dog). However, almost all known canine point mutations remain uncharacterised (Chang and others 2007). To the best of our knowledge, no other group has studied β2M mutations in canine mammary gland tumours. Therefore, the aim of the present study was to determine β2M mutations in canine mammary gland simple and complex carcinomas.
Materials and methods
Approximately 1 g tissue samples were collected from the mammary gland tissues of seven healthy beagles, from the tumours of 11 dogs with mammary gland tumours (one Shih Tzu, two Labrador retrievers, two mixed breeds, one Welsh corgi, two toy poodles, one great Pyrenees, and two papillons), and from normal …