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N Nakao, M Tanaka, Y Higashimoto, and K Nakashima

Insulin receptor (IR) and IGF-I receptor (IGF-IR) are structurally and functionally related and belong to the tyrosine kinase receptor family. In teleosti such as salmonids and turbot, occurrence of multiple IR and IGF-IR members has been reported, but the structures of a complete set of both IR and IGF-IR members in a single teleost species have not yet been characterized. In this study, we cloned and analysed four distinct cDNA clones for IR and IGF-IR members from the liver and kidney of the Japanese flounder (Paralichthys olivaceus). Deduced amino acid sequence analyses and phylogenetic analysis have revealed that two of them (fIR-1 and fIR-2) belong to IR members and the other two (fIGF-IR-1 and fIGF-IR-2) are IGF-IRs. fIR-1 and fIR-2 comprised 1369 and 1368 amino acid residues respectively, and fIGF-IR-1 and fIGF-IR-2 comprised 1412 and 1418 residues respectively. All the receptor proteins contained cysteine-rich domains in their alpha-subunits, and conserved each transmembrane and tyrosine kinase domains in their beta-subunits. The amino acid sequences of fIRs and fIGF-IRs showed more than 90% sequence identity with turbot IR and IGF-IR respectively. When compared with their mammalian homologues, fIGF-IR-1 and fIGF-IR-2 proteins contained large insertions at their C-termini, as was observed in the corresponding region of turbot IGF-IR. Occurrence of multiple species of mRNA for each IR and IGF-IR was suggested by Northern blot analyses. A ribonuclease protection assay revealed diverse expressions of four receptor mRNAs in a wide range of tissues including heart, liver, ovary, testis, brain, gill arch, kidney, skeletal muscle, intestine, stomach, spleen and eye of the flounder.

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N Nakao, Y Higashimoto, T Ohkubo, H Yoshizato, N Nakai, K Nakashima, and M Tanaka

Growth hormone receptor (GHR) cDNA and gene of the Japanese flounder (Paralicthys olivaceus) were cloned and their molecular structures were characterized. The 641 amino acid sequence predicted from the cDNA sequence showed more than 75% overall sequence similarity with GHRs of other teleosts such as turbot and goldfish, and contained common structural features of vertebrate GHRs. The extracellular domain of flounder GHR had three pairs of cysteines and an FGEFS motif with a replacement E to D. The cytoplasmic domain contained two conserved motifs referred to as box 1 and box 2. The flounder GHR gene was cloned by PCR using primers designed from the sequence of the GHR cDNA. The GHR gene was composed of 10 exons. The sequence of exon 1 corresponded to the 5'-untranslated region of the cDNA, and exons 2-6 encoded most parts of the extracellular domain. The transmembrane domain was found in exon 7, and the intracellular domain was encoded in exons 8-10. Exon 10 also encoded the 3'-untranslated region. Comparison of the flounder GHR gene with the human GHR gene shows that the flounder gene contains no exons corresponding to exon 3 of the human GHR gene, and that the region corresponding to exon 10 in the human GHR gene is encoded by exons 9 and 10 in the flounder GHR gene. These findings indicate that the flounder GHR gene diverged from those of mammalian and avian GHR genes, especially in the organization of the exons encoding the cytoplasmic domain. In addition to the regular form of GHR mRNA, a 3'-truncated form lacking the region derived from exons 9 and 10 was detected as a minor species in the liver by RT-PCR and by RNase protection assay. RT-PCR analysis showed that both the regular and the 3'-truncated GHR mRNAs are expressed in a wide range of flounder tissues with the highest levels being found in the liver. The 5'-flanking region of the flounder GHR gene was cloned by inverse PCR, and three transcription start points were identified with similar frequency by RNase protection assay.

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N Hama, H Itoh, S Suga, Y Komatsu, T Yoshimasa, and K Nakao


C-type natriuretic peptide (CNP), the third member of natriuretic peptides, has recently been discovered from the porcine brain. Using a polyclonal antiserum to CNP, we demonstrated that CNP-like immunoreactivity (CNP-LI) is present mainly in the central nervous system. Recently, however, we have discovered the production and secretion of CNP in vascular endothelial cells. These observations suggested that CNP may act not only as a neuropeptide but also as a local regulator of vascular tone or growth. In order to further clarify the pathophysiological significance of CNP, we aimed at the preparation of a monoclonal antibody to CNP.

A monoclonal antibody to CNP, KY-CNP-I, has been produced. This monoclonal antibody belongs to the immunogloblin G1 subclass and has high affinity for CNP. Using this monoclonal antibody, we established a specific radioimmunoassay (RIA) for CNP. The RIA detected CNP-LI in rat brain extracts and culture media conditioned with bovine endothelial cells. In addition, the pretreatment of cultured aortic smooth muscle cells with KY-CNP-I attenuated cyclic GMP production induced by CNP in vitro. The preadministration of KY-CNP-I to rats also attenuated plasma cyclic GMP increase after intravenous injection of CNP in vivo.

These results indicate that this monoclonal antibody is a useful tool to clarify the pathophysiological role of CNP as a neuropeptide and as a local vascular regulator.

Journal of Endocrinology (1994) 141, 473–479

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H. Imura, Y. Kato, Y. Nakai, K. Nakao, I. Tanaka, H. Jingami, T. Koh, T. Yoshimasa, T. Tsukada, M. Suda, M. Sakamoto, N. Morii, H. Takahashi, K. Tojo, and A. Sugawara


Advances in techniques in molecular biology have facilitated the research into endogenous opioids and related peptides in several ways. The organization and expression of genes and the primary structure of three precursor proteins of opioid peptides have been elucidated. These studies predicted the presence of potentially bioactive peptides, which has been confirmed by later studies. Advances in techniques in protein chemistry have helped to elucidate the distribution and molecular forms of endogenous opioids and related peptides in the body, and the processing of precursor proteins. Studies on the function of these peptides have shown a broad spectrum of actions. Leumorphin, a newly identified peptide, has been shown to exhibit unique biological activities. In spite of extensive studies, the physiological and pathophysiological significance of opioid peptide systems are not yet completely understood. This is mainly due to the paucity of our knowledge about opioid receptors. Further studies on the subtypes of opioid receptors will help to elucidate all aspects of the function of endogenous opioids and related peptides.

J. Endocr. (1985) 107, 147–157