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Department of Zoology, University of Hong Kong, Hong Kong, People’s Republic of China
Address all correspondence and requests for reprints to: Dr. Anderson O. L. Wong, Associate Professor, Department of Zoology, University of Hong Kong, Pokfulam Road, Hong Kong SAR, People’s Republic of China. E-mail: olwong{at}hkucc.hku.hk.
Calmodulin (CaM) is a Ca2+-binding protein essential for biological functions mediated through Ca2+-dependent mechanisms. In the goldfish, CaM is involved in the signaling events mediating pituitary hormone secretion induced by hypothalamic factors. However, the structural identity of goldfish CaM has not been established, and the neuroendocrine mechanisms regulating CaM gene expression at the pituitary level are still unknown. Here we cloned the goldfish CaM and tested the hypothesis that pituitary expression of CaM transcripts can be the target of modulation by hypothalamic factors. Three goldfish CaM cDNAs, namely CaM-a, CaM-bS, and CaM-bL, were isolated by library screening. These cDNAs carry a 450-bp open reading frame encoding the same 149-amino acid CaM protein, the amino acid sequence of which is identical with that of mammals, birds, and amphibians and is highly homologous (
90%) to that in invertebrates. In goldfish pituitary cells, activation of cAMP- or PKC-dependent pathways increased CaM mRNA levels, whereas the opposite was true for induction of Ca2+ entry. Basal levels of CaM mRNA was accentuated by GnRH and pituitary adenylate cyclase-activating polypeptide but suppressed by dopaminergic stimulation. Pharmacological studies using D1 and D2 analogs revealed that dopaminergic inhibition of CaM mRNA expression was mediated through pituitary D2 receptors. At the pituitary level, D2 activation was also effective in blocking GnRH- and pituitary adenylate cyclase-activating polypeptide-stimulated CaM mRNA expression. As a whole, the present study has confirmed that the molecular structure of CaM is highly conserved, and its mRNA expression at the pituitary level can be regulated by interactions among hypothalamic factors.
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  Q. Jiang, W. K. W. Ko, E. A. Lerner, K. M. Chan, and A. O. L. Wong Grass carp somatolactin: I. Evidence for PACAP induction of somatolactin-{alpha} and -{beta} gene expression via activation of pituitary PAC-I receptors Am J Physiol Endocrinol Metab, August 1, 2008; 295(2): E463 - E476. [Abstract] [Full Text] [PDF]
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 K. H. Sze, H. Zhou, Y. Yang, M. He, Y. Jiang, and A. O. L. Wong Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) as a Growth Hormone (GH)-Releasing Factor in Grass Carp: II. Solution Structure of a Brain-Specific PACAP by Nuclear Magnetic Resonance Spectroscopy and Functional Studies on GH Release and Gene Expression Endocrinology, October 1, 2007; 148(10): 5042 - 5059. [Abstract] [Full Text] [PDF]
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X. Wang, M. M. S. Chu, and A. O. L. Wong Signaling mechanisms for {alpha}2-adrenergic inhibition of PACAP-induced growth hormone secretion and gene expression grass carp pituitary cells Am J Physiol Endocrinol Metab, June 1, 2007; 292(6): E1750 - E1762. [Abstract] [Full Text] [PDF]
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A. O. L. Wong, W. Li, C. Y. Leung, L. Huo, and H. Zhou Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) as a Growth Hormone (GH)-Releasing Factor in Grass Carp. I. Functional Coupling of Cyclic Adenosine 3',5'-Monophosphate and Ca2+/Calmodulin-Dependent Signaling Pathways in PACAP-Induced GH Secretion and GH Gene Expression in Grass Carp Pituitary Cells Endocrinology, December 1, 2005; 146(12): 5407 - 5424. [Abstract] [Full Text] [PDF]
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