MHC-DRB AND MHC-DQA1 NUCLEOTIDE-SEQUENCES OF 3 LOWLAND GORILLAS - IMPLICATIONS FOR THE EVOLUTION OF PRIMATE MHC CLASS-II HAPLOTYPES

Mhc-DRB and -DQA1 second-exon and -DRB 3'-untranslated-region nucleoti de sequences of three lowland gorillas with no known family relationsh ip with each other and of two HLA homozygous typing cell lines were de termined and compared with published primate Mhc-DRB and -DQA1 sequenc es. Eleven distinct MhcGogo-DRB second-exon sequences were found, whic h represent the gorilla counterparts of the HLA-DRB103, -DRB1*-10, -D RB3, -DRB5, and -DRB6 allelic lineages. One Gogo-DRB second-exon seque nce does not have an obvious human counterpart and is tenatively desig nated Gogo-DRBY01. The gorilla equivalents of the HLA-DRB2 and -DRB8 loci were identified as judged on Mhc-DRB 3'-untranslated-region seque nces. In addition, four different Gogo-DQA1 alleles belonging to three different allelic lineages were detected. The Mhc-DRB-DQA1 haplotypes of these gorillas were deduced based on the obtained Mhc-DRB and -DQA 1 sequences and the two published Mhc-DRB haplotypes of the lowland go rilla Sylvia. All deduced Gogo-DRB-DQA1 haplotypes show gene constella tions different from known HLA-DRB-DQA1 haplotypes, while some of the Gogo-DRB haplotypes presented here contain more DRB genes than the HLA -DRB haplotypes. Based on phylogenetic trees, bootstrap analyses, and the gorilla, chimpanzee, and human Mhc-DRB haplotypes described, we pr opose that at least two Mhc-DRB loci, here tentatively designated Mhc- DRBI and -DRBII, existed on an ancient primate Mhc-DRB haplotype. The Mhc-DRB101, -DRB1*02 (-DRB1*15 and -DRB1*16), -DRB1*03 (-DRB1*03, -DR B108, -DRB1*11, -DRB1*12, -DRB1*13, and DRB1*14), and -DRB1*10 alleli c lineages and -DRB3 and -DRBY loci probably evolved from the hypothet ical primate Mhc-DRBI locus, whereas the present primate Mhc-DRB2, -DR B4, and -DRB6 loci originate from the ancient Mhc-DRBII locus of this core primate Mhc-DRB haplotype.