Fish growth hormone receptor:: Molecular characterization of two membrane-anchored forms

A RT-PCR approach was used to clone and sequence the full-length growth hormone receptor (GHR) of a teleost fish, the turbot (Scophthalmus maximus). Total liver RNA was amplified by RT-PCR with degenerate primers designed in extracellular and cytoplasmic regions, and a single DNA fragment of 1100 bp was obtained. The entire coding region was obtained by 5' and 3' RACE assays, and comprises an open-reading frame of 633 amino acids. This sequence shows the characteristic motifs of the class I cytokine receptor superfamily, and its amino acid identity with mammalian, avian, reptilian and amphibian GHRs is 32-36%. The 3' RACE also revealed the occurrence of an alternate messenger encoding a membrane-anchored truncated receptor, which could facilitate the production of GH-binding protein in fish species. This report represents the first data on fish GHR sequence, and it provides evidence for the conservation of this receptor throughout vertebrate evolution.