FATE OF A REDUNDANT GAMMA-GLOBIN GENE IN THE ATELID CLADE OF NEW-WORLD MONKEYS - IMPLICATIONS CONCERNING FETAL GLOBIN GENE-EXPRESSION

Conclusive evidence was provided that gamma 1, the upstream of the two linked simian gamma-globin loci (5'-gamma(1)-gamma 2-3'), is a pseudogene in a major group of New World monkeys. Sequence analysis of PCR-amplified genomic fragments of predicted sizes revealed that all extant genera of the platyrrhine family Atelidae [Lagothrix (woolly monkeys), Brachyteles (woolly spider monkeys), Ateles (spider monkeys), and Alouatta (howler monkeys)] share a large deletion that removed most of exon 2, all of intron 2 and exon 3, and much of the 3' flanking sequence of gamma(1). The fact that two functional gamma-globin genes were not present in early ancestors of the Atelidae (and that gamma(1) was the dispensible gene) suggests that for much or even all of their evolution, platyrrhines have had gamma(2) as the primary fetally expressed gamma-globin gene, in contrast to catarrhines (e.g., humans and chimpanzees) that have gamma(1) as the primary fetally expressed gamma-globin gene. Results from promoter sequences further suggest that all three platyrrhine families (Atelidae, Cebidae, and Pitheciidae) have gamma(2) rather than gamma(1) as their primary fetally expressed gamma-globin gene. The implications of this suggestion were explored in terms of how gene redundancy, regulatory mutations, and distance of each gamma-globin gene from the locus control region were possibly involved in the acquisition and maintenance of fetal, rather than embryonic, expression.