No abstract

In mammals, growth hormone-releasing hormone (GHRH), acting via the GHRH receptor, plays an important role in the regulation of growth hormone (GH) synthesis and secretion as well as the proliferation and differentiation of somatotropes in the pituitary. In fishes, information concerning the functional role of the characterized GHRHs is limited. For that reason, a putative goldfish GHRH receptor cDNA was characterized in this study. The receptor cDNA is 2,243 bp in length, encoding a 438-amino-acid-long polypeptide with 7 putative transmembrane-spanning regions, which is a characteristic of G-protein-coupled receptors. The receptor, when expressed in COS-7 cells, showed minimal responses (2-fold cAMP responses) when stimulated with 100 nM of human GHRH, pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP). However, this receptor was found to be specific for a carp GHRH-like peptide isolated from the brain of common carp (Cyprinus carpio); there was a significant and dose-dependent increase in intracellular cAMP (a maximum response of 22-fold increase with an EC₅₀ of 0.1 nM) when the transfected cells were stimulated with this peptide. As a preliminary study to investigate the functional role of this receptor, the tissue distribution of the mRNA was analyzed by reverse-transcription-polymerase chain reaction. The receptor mRNA was found to be present in the brain, pituitary, gut, gill, heart, liver, skeletal muscle, spleen, ovary and testis. Together with a goldfish PACAP type 1 receptor and a VIP1 receptor recently isolated in our laboratory, characterization of this putative GHRH receptor provides the molecular basis for the future understanding of the neuroendocrine control of growth and reproduction by these neuropeptides in goldfish as well as other teleosts.

Jaundice is common in ethnic Chinese infants, but to our knowledge Crigler-Najjar syndrome (CN syndrome) type I has never been reported in China. A Chinese girl with severe jaundice was recently diagnosed to have CN syndrome type I by analyzing the bilirubin-uridinediphospho (UDP)-glucuronosyltransferase gene (UGT1A1). The patient was homozygous for a nonsense mutation that replaced glutamine (CAG, amino acid 239) with stop codon (TAG) at nucleotide number 715 (715C-->T) in exon 1. No mutation was found in exons 2-5. Her parents were heterozygous for the same mutant. The patient had an average bilirubin level of 300-500 mumol/L and a peak of 701 mumol/L. Daily phototherapy for 15 h was required to keep the bilirubin levels within 280-320 mumol/L. The unconjugated hyperbilirubinaemia apparently resulted from homozygous nonsense mutation of UGT1A1, which could completely abolish the UGT activity towards bilirubin (hepatic glucuronidation) and result in CN syndrome type I. Identification of the genetic defect is very useful for gene therapy, especially for DNA/RNA chimera therapy, and can be used as an antenatal screening test to identify the affected offsprings.