CONSERVATIVE EVOLUTION OF THE MHC-DP REGION IN ANTHROPOID PRIMATES

To determine the organization of the DP region in the Mhc of anthropoi d primates, we constructed contig maps from cosmid clones of the chimp anzee and orangutan, representatives of the infraorder Catarrhini, as well as of the cotton-top tamarin, a representative of the infraorder Platyrrhini. We found the maps to be remarkably similar to each other and to the previously published map of the human DP region. In each of the four species, the DP region consists of four loci arranged in the same order (DPB2 . . . DPA2 . . . DPB1 . . . DPA1) and in the same tr anscriptional orientation (tail-to-tail). The regions in the four spec ies are of approximately the same length and many of the restriction s ites are shared between species. The inserts of most Alu elements, of a ribosomal protein pseudogene, and of an IgCepsilon-like pseudogene a re found in corresponding positions in all four species. The data indi cate that the human-type organization of the DP region was established before the divergence of the Catarrhini and Platyrrhini lines more th an 37 million years ago and that it has remained principally intact si nce that time. This conservation of the DP region is in striking contr ast to the evolutionary instability of certain other Mhc regions, in p articular those occupied by the DRB or C4 and CYP21 loci. We interpret the stability of the DP region as an indication that the region is be ing phased out functionally.