Characterization of the chicken genomic growth hormone gene (Wai Chow strain)

Abstract

Genomic chicken growth hormone gene (cGH), similar to that of mammalian GH, has been reported to consist of five exons and four introns. However, the introns of the cGH gene are significantly larger than those reported in mammalian growth hormone genes, and the 5’-flanking region where regulatory sequences are located also shares only little homology with other mammalian GH genes. Therefore, the present study investigates the genomic structure of a Chinese strain chicken GH gene and the cis-regulatory elements located in the promoter region. Genomic DNA clones containing the cGH gene and its promoter have been isolated from a genomic library constructed from a Chinese strain chicken, Wai Chow. The cGH gene was subcloned and subjected to PCR sequence analysis. There are 8 additions and 26 substitutions found in intron regions of the cGH gene as compared to previous published data, whereas there is only 1 silent substitution (CTC, Leu to CTG, Leu) found at position 2338bp in exon 4. In addition, a 500 base pairs fragment upstream from the transcription start site has also been cloned and sequenced. Result shows that there is a single base pair deletion located at 5 base pairs upstream from a proposed TATA box. Deletion analysis on the 500 base pairs fragment will be carried out using a reporter gene system to study the cis-regulatory elements at the promoter region. Characterization of the promoter region will elicit the molecular regulation of GH gene expression in chicken.