CLONING AND CHARACTERIZATION OF A CHICK-EMBRYO CDNA AND GENE FOR IGF-BINDING PROTEIN-2

We have isolated and characterized a cDNA for IGF-binding protein-2 (I GFBP-2) and its gene from the chick embryo. Using primers from a conse rved region of the mammalian IGFBP-2 sequence, a cDNA clone (1.6 kb) w as isolated from an embryonic day-18 chick retina cDNA library. Althou gh the clone was truncated at the 5' end,the complete coding sequence was obtained from 5' rapid amplification of cDNA ends and genomic sequ encing. The open reading frame encoded a 311 amino acid precursor prot ein which contains a putative 36 residue signal peptide. The mature 27 5 amino acid protein had a predicted M(r) of 33 500 and exhibited 71, 68, 68 and 66% identity to rat, bovine, ovine and human IGFBP-2 cDNA r espectively, with conservation of all 18 cysteines. The cDNA contained an RGD peptide but lacked a putative ATP-binding motif. A single tran script of approximately 2.3 kb was present in embryonic day-15 eye, br ain, skeletal muscle, heart and intestine, but was virtually absent fr om embryonic day-15 liver. The chicken IGFBP-2 gene spanned approximat ely 38 kb, consisted of four exons, and was similarly organized to tha t of the rat and human. Southern blot analysis of chicken genomic DNA suggested that it is encoded by a single gene. The sequence informatio n from the avian IGFBP-2 should be of value in examining the role of I GFBP-2 in vertebrate development.