Goldfish calmodulin: molecular cloning, tissue distribution, and regulation of transcript expression in goldfish pituitary cells.
Calmodulin (CaM) is a Ca(2+)-binding protein essential for biological functions mediated through Ca(2+)-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 Ca(2+) 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.
Huo
Longfei
L
Department of Zoology, University of Hong Kong, Pokfulam Road, Hong Kong SAR, People's Republic of China.
Lee
Eric K Y
EK
Leung
P C
PC
Wong
Anderson O L
AO
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000235:genetics* / Q000378:metabolism; D003001:Cloning, Molecular; D000242:Cyclic AMP / Q000378:metabolism; D004298:Dopamine / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D006054:Goldfish / Q000235:genetics*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D008969:Molecular Sequence Data; D009479:Neuropeptides / Q000494:pharmacology; D010802:Phylogeny; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D010902:Pituitary Gland / Q000166:cytology / Q000502:physiology*; D011493:Protein Kinase C / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis
D002147:Calmodulin; D009479:Neuropeptides; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D012333:RNA, Messenger; D007987:Gonadotropin-Releasing Hormone; D000242:Cyclic AMP; D011493:Protein Kinase C; D002118:Calcium; D004298:Dopamine