Both serological and DNA sequence analyses were performed to determine the extent of genetic polymorphism in Q region genes. A panel of Qa-2-specific monoclonal antibodies (mAbs) was tested on 35 wildderived and inbred mouse strains. Members of this reagent panel recognize multiple and distinct epitopes on the Qa-2-bearing molecule(s). Although quantitative variations in Qa-2 levels were observed, no structural polymorphisms were detected. All strains were either entirely positive or entirely negative with the complete set of reagents. Moreover, cell surface Qa-2 expression was not significantly affected by differences in age or sex of the mouse or cell cycle status. To confirm this apparent lack of genetic polymorphism, the polymerase chain reaction (PCR) technique was used to amplify a portion of the 3′ end of the Q region genes, Q4 to Q9, from several independent wild-derived strains of mice. Sequence analysis of the amplified material revealed very little evidence of nucleotide divergence. All strains tested had a Q even DNA sequence identical to that of Q6/Q8 in the B10 strain. Likewise, all tested strains had a Q odd DNA sequence identical to Q7/Q9 in the B10 strain. Two strains showed additional Q even sequences, while all strains tested possessed additional Q odd sequences. The observed lack of polymorphism suggests that the Q genes have evolved in a different manner from H-2K and H-2D. Moreover, duplications of these genes appear to have arisen prior to nucleotide sequence divergence.
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