Characterization of a novel growth hormone receptor-encoding cDNA in rainbow trout and regulation of its expression by nutritional state

• A novel member of the (GHR) family was characterized in a teleost fish
• The mRNA encoded a 657-amino acid protein, denoted GHR1
• GHR mRNA was expressed widely and was most abundant in liver and muscle
• Fasting reduced expression of GHR1 mRNA in liver, adipose, and red and white muscle
• The divergence of the GHRs was clarified and a nomenclature is proposed and GHRs

To clarify the divergence of the growth hormone receptor (GHR) family, we characterized a novel GHR from a teleost fish (rainbow trout). A 2357-nt cDNA was isolated and found to contain a single initiation site 71 nt from the most 5′ end, an open reading frame of 1971 nt encoding a 657-amino acid protein, and a single polyadenylation site 229 nt from the poly-A tail. Based on structural analysis, the protein was identified as a type 1 GHR (GHR1). The new GHR1 shares 42% and 43% amino acid identity, respectively, with GHR2a and GHR2b, the two type 2 GHRs isolated from trout previously. GHR1 mRNA was found in a wide array of tissues with the highest expression in the liver, red muscle, and white muscle. Fasting animals for 4 weeks reduced steady state levels of GHR1 in the liver, adipose, and red muscle. These findings help clarify the divergence and nomenclature of GHRs and provide insight into the function of duplicated GHR types.