Submitted to: Comparative Endocrinology International Congress Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: February 1, 2005
Publication Date: May 22, 2005
Citation: Small, B.C., Waldbieser, G.C., Murdock, C.A., Peterson, B.C. Molecular cloning, genomic organization and functional characterization of channel catfish growth hormone receptor: Changes in hepatic GHR mRNA expression following fasting and feeding exogenous cortisol. Proc. XV International Conference of Comparative Endocrinology, Boston, MA. p. 120. Technical Abstract: The full-length channel catfish (Ictalurus punctatus) growth hormone receptor (GHR) was cloned from liver cDNA by reverse transcription-polymerase chain reaction (RT-PCR) and random amplification of 5' and 3' cDNA ends (RACE). Sequence analysis revealed an open reading frame that codes for a mature 555 amino acid protein with characteristic GHR motifs. Bacterial artificial chromosome (BAC) sequencing, RT-PCR, and genomic PCR indicate that the GHR gene encompasses five exons. A tetranucleotide microsatellite repeat (GATG)7 was identified in the 3' non-translated region and amplified from genomic DNA. Four alleles were identified in a population of 36 randomly bred catfish, and average heterozygosity in this population was 62%. Two reference full-sib families were genotyped and allelic inheritance permitted placement of the GHR locus on the channel catfish genetic linkage map. A real-time RT-PCR assay was used to measure GHR mRNA expression in the liver of channel catfish which were fasted, fed a standard feed, or fed a cortisol-laden feed for four weeks. Levels of hepatic GHR mRNA were lower in cortisol-fed and fasted fish compared to fed fish, and were positively correlated to circulating IGF-I levels. These results suggest that a reduction in hepatic GHR gene expression might serve as a mechanism for the reduction of circulating IGF-I in channel catfish during periods of long-term fasting and stress.