FETAL GLOBIN EXPRESSION IN NEW-WORLD MONKEYS

Reverse phase chromatography of the globin chains of adult, newborn, a nd fetal erythrocytes from three species of New World monkeys (Cebus a pella, Aotus azarae, and Callithrix jacchus) representing three of the seven platyrrhine clades showed that gamma-globin expression was feta l in these animals, The globins were identified by a combination of ch emical sequencing and mass spectro metric analysis, Since gamma-globin expression is fetal in the other major simian branch, the catarrhines , but embryonic in prosimian primates and nonprimate placental mammals , the evolution of fetal recruitment can now be assigned to the period between the simian-prosimian divergence (55 million years ago) and th e platyrrhine-catarrhine divergence (35 million years ago), The gamma- globin gene underwent tandem duplication during the same evolutionary epoch, in accord with a model that suggests that the downstream duplic ated gamma-gene (gamma 2) was free to acquire the mutations necessary for fetal recruitment, Mass spectrometric analysis of tryptic digests of the gamma-globins verified the amino acid sequences deduced from ge nomic sequencing, Detailed analysis of high performance liquid chromat ography and matrix-assisted laser desorption/ionization mass spectrome try data showed that gamma 2-globin in Cebus was expressed to a far gr eater extent than gamma 1-globin, supporting inferences drawn from a s tudy of the promoter sequences, A ''pre-gamma''-globin was observed in C. apella and shown to be primarily the glutathionyl adduct, The othe r species, A. azarae and C. jacchus, also express only one gamma-globi n polypeptide. This work provides biochemical evidence of an evolution ary trend in the platyrrhines to alter the duplicated gamma-globin gen e locus so that only one gamma-globin polypeptide is expressed.