MHC-DRB GENES OF PLATYRRHINE PRIMATES

The two infraorders of anthropoid primates, Platyrrhini (New World mon keys) and Catarrhini (Old World monkeys and the hominoids) are estimat ed to have diverged from a common ancestor 37 million years ago. The m ajor histocompatibility complex class II DRB gene and haplotype polymo rphism of the Catarrhini has been characterized in several recent stud ies. The present study was undertaken to obtain information on the DRB polymorphism of the Platyrrhini. Fifty-five complete exon 2 DRB seque nces were obtained from six species of Platyrrhini representing both t he Callitrichidae and the Cebidae families. Combined with the results of a parallel contig mapping study, our data indicate that at least th ree loci (DRB103, DRB3, and DRB5) are shared by the Catarrhini and th e Platyrrhini. However, the three loci are occupied by functional gene s in the former infraorder and mostly by pseudogenes in the latter. In stead of the pseudogenes, the Platyrrhini have evolved a new set of ap parently functional genes - DRB11 and DRBW12 through DRB*W19, which h ave thus far not been found in the Catarrhini. The DRBW13, *W14, *W15 , W17, *W18, and *W19 genes seem to be restricted to the Cebidae fami ly, whereas the DRBW16 locus has so far been documented in the Callit richidae family only. The DRB alleles of the cotton-top tamafin, and p erhaps also those of the common marmoset (both members of the family C allitrichidae), are characterized by low nucleotide diversity, possibl y indicating that they diverged from a common ancestral gene relativel y recently.