The Involucrin Genes of the White-fronted Capuchin and Cottontop Tamarin: The Platyrrhine Middle Region ’ zyxwvutsrqpo Marjorie Phillips, * Robert H. Rice, * Philippe Djian,? and Howard Green- f *Department of Environmental Toxicology, University of California, Davis; and TDepartment of Cellular and Molecular Physiology, Harvard Medical School In all anthropoid species, the coding region of the involucrin gene contains a segment of short tandem repeats that were added sequentially, beginning in a common anthropoid ancestor. The involucrin coding region of each of two platyrrhine species, the white-fronted capuchin (Cebus albifrons) and the cottontop tamarin (Saguinus Oedipus), has now been cloned and sequenced. These genes share with the genes of the catarrhines the repeats added in the common anthropoid lineage (the early region). After their divergence, the platyrrhines, like the catarrhines, continued to add repeats vectorially 5’ of the early region, to form a middle region. The mechanism that was established in the common anthropoid lineage for the addition of repeats at a definite site in the coding region was transmitted to both platyrrhines and catarrhines, enabling each to generate its middle region independently. The process of vectorial repeat addition continued in two platyrrhine sublineages after their divergence from each other. Introduction Involucrin is a specialized protein of the keratinocyte of the epidermis and other stratified squamous epithelia. During terminal differentiation of the cell, involucrin becomes cross-linked to other ljroteins in a reaction that is catalyzed by transgluta- minase (Rice and Green 1977, 1979) and that results in the formation of an insoluble envelope beneath the plasma membrane (Sun and Green 1976; Green 1977). The coding region of the involucrin gene lies within a single exon and contains a segment of tandem repeats. While the parts of the coding region flanking the segment of repeats are homologous in all animals so far examined, the segment of repeats of the anthropoid primates differs from that of the prosimians and nonprimate mammals in its location within the cqding region, its repeat length, and the nucleotide sequence of the repeats (Eckert and Green 1986; Tseng and Green 1988, 1989, 1990; Djian and Green 1989a, 19896, 1990; Teumer and Green 1989; Phillips et al. 1990). It was concluded that an earlier segment of repeats homologous to that of the prosimians was excised in an ancestor of anthropoid primates and that a modern segment of repeats was generated by successive duplications of a 1 0-codon sequence located else- where in the coding region (Tseng and Green 1988). Of the numerous repeats in the modem segment of the anthropoids, only the 10 3’-most repeats (the early region) are shared by species as diverse as the owl monkey 1. Key words: involucrin genes, Cebus albifrons, Saguinus Oedipus, white-fronted capuchin, cottontop tamarin, primate evolution, internal repeals. Address for correspondence and reprints: Howard Green, Department of Cellular and Molecular Phys- iology, Harvard Medical School, 25 Shattuck Street, Boston, Massachusetts 02 115 Mol. Biol. Evol. 8(5):579-59 I. 199 I. 0 I99 I by The University of Chicago. All rights reserved. 0737-4038/91/0805-0002$02.00 579