The characterization of prepro-Insulin-like growth factor-1 Ea-2 expression and Insulin-like growth factor-1 genes (devoid 81 bp) in the zebrafish (Danio rerio)

In this study, we cloned zebrafish (Danio rerio) IGF-1 cDNA and gene from zebrafish brain cDNA library and adult zebrafish genomic library, respectively. Based on two cDNAs sequence with different length of 5 '- and 3 ' -untranslated region (5UTR and 3UTR) and one nucleotide difference at glutamine (A9, GAG) of A domain represented at IGF-1 sequence. One of zebrafish IGF-1 genes named as IGF-la gene. The zebrafish IGF-la gene spanned approximately 15 kb and is divided into five exons. The results of IGF-1 cDNA and genomic Southern blotting, all indicated that the zebrafish have more than one IGF-1 gene. The genomic organization of zebrafish IGF-la gene in an exon is devoid of 81 bp segment which is located at 3 ' end of exon 3 encoded 27 amino acid of E domain. The segment of 27 amino acid exists in known teleost IGF-1 genes but is absent in zebrafish IGF-1 gene. The E domain of zebrafish IGF-1 Ea-2 is encoded by 3 ' end of exon 3 (16 amino acid), full of exon 4 (12 amino acid) and exon 5 (19 amino acid). The sequence data revealed the zebrafish IGF-la gene encoded IGF-la Ea-2 mRNA. In combination RT-PCR with Southern blotting, zebrafish IGF-1 genes abundantly expressed IGF-1 Ea-2 mRNA in all tested adult tissues and developmental stages of embryo. The IGF-1 Ea-2 mRNA was first detected during embryo development from blastula stage to hatching, during yolk absorption and at feeding. All these findings suggest that the expression of pro-IGF-1 Ea-2 is not controlled by alternative splicing but alternative gene usage in the zebrafish. (C) 2001 Elsevier Science B.V. All rights reserved.