This chapter examines the structure and evolution of fish growth hormone and insulin-like growth factor genes. Growth hormone (GH), prolactin (PRL), placental lactogen (PL), and somatolactin (SL) form a family of polypeptide hormones with common structural and overlapping biological characteristics. The chapter presents a study in which amino acid sequence comparisons were carried out for GHs by aligning the conserved half-cystine residues and by introducing several deletions to maximize the homology. A comparison of structural characteristics between the fish GHs and hGH was executed using the Wisconsin GCG program package. The somatolactin precursor is a single-chain polypeptide of approximately 231 amino acid residues. Although the amino acid homology among SL, GH, and PRL is low, they are structurally related to one another because four of the six cysteine residues are present in positions similar to those in GH and PRL polypeptides. GH, PRL, and SL are all known to be actively involved in the osmoregulatory responses of teleosts. This suggests thatthat the GH-family ancestral gene may have been involved in the osmoregulation response of the deuterostome-invertebrate ancestors of chordates.
ASJC Scopus subject areas
- Animal Science and Zoology