RFLP analysis of the HLA-, ChLA-, and RhLA-DQ alpha chain gene regions: conservation of restriction sites during evolution.

Genomic DNA samples, derived from a panel of 60 chimpanzees and 45 rhesus monkeys, were digested with the restriction enzymes Taq I and Bgl II and hybridized with an HLA-DQ alpha chain cDNA probe. The results were compared with the data available on a human reference panel. Use of the restriction enzyme Taq I and the DQ alpha chain probe allows the detection of five HLA-DQA1 and two HLA-DQA2 gene-associated fragments within the human population. For the ChLA and RhLA systems, 3 and 7 different DQA1-associated restriction patterns were detected, respectively, while for the chimpanzee a nonpolymorphic DQA2 (DX alpha) gene-associated fragment was also observed. The equivalent of the HLA- and ChLA-DQA2 genes appears to be absent in the rhesus monkey. The ChLA-DQA1 and -DQA2 gene-associated RFLP patterns are identical in man and chimpanzee, whereas such restriction site conservation is not seen in the rhesus monkey. The conclusion drawn is that the genetic organization of the HLA-DQA and ChLA-DQA gene regions, and possibly some of their allelic variabilities, already existed before man and chimpanzee separated in evolution. Moreover, the particular duplication which led to the generation of the HLA- and ChLA-DQA2 genes must have happened before speciation of members belonging to the superfamily Hominoidea (man, chimpanzee, etc), but probably after the separation of superfamily Cercopitecoidea (rhesus monkeys, baboons, etc.) from Hominoidea.