Grass carp somatolactin: I. Evidence for PACAP induction of somatolactin-alpha and -beta gene expression via activation of pituitary PAC-I receptors.
Somatolactin (SL), the latest member of the growth hormone/prolactin family, is a novel pituitary hormone with diverse functions. At present, SL can be identified only in fish but not in tetrapods and its regulation at the pituitary level has not been fully characterized. Using grass carp as a model, we examined the direct effects of pituitary adenylate cyclase-activating polypeptide (PACAP) on SL secretion and synthesis at the pituitary cell level. As a first step, the structural identity of grass carp SL, SLalpha and SLbeta, was established by 5'/3'-rapid amplification of cDNA ends. These two SL isoforms are single-copy genes and are expressed in two separate populations of pituitary cells located in the pars intermedia. In the carp pituitary, PACAP nerve fibers were detected in the nerve tracts of the neurohypophysis and extended into the vicinity of pituitary cells forming the pars intermedia. In primary cultures of grass carp pituitary cells, PACAP was effective in stimulating SL release, cellular SL content, and total SL production. The increase in SL production also occurred with parallel rises in SLalpha and SLbeta mRNA levels. With the use of a combination of molecular and pharmacological approaches, PACAP-induced SL release and SL gene expression were shown to be mediated by pituitary PAC-I receptors. These findings, as a whole, suggest that PACAP may serve as a hypophysiotropic factor in fish stimulating SL secretion and synthesis at the pituitary level. Apparently, PACAP-induced SL production is mediated by upregulation of SLalpha and SLbeta gene expression through activation of PAC-I receptors.
Jiang
Quan
Q
Endocrinology Division, School of Biological Sciences, University of Hong Kong, Pokfulam Road, Hong Kong SAR, P.R. China.
Ko
Wendy K W
WK
Lerner
Ethan A
EA
Chan
K M
KM
Wong
Anderson O L
AO
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D015139:Blotting, Southern; D002347:Carps / Q000502:physiology*; D003001:Cloning, Molecular; D029941:Fish Proteins / Q000096:biosynthesis* / Q000235:genetics; D006023:Glycoproteins / Q000096:biosynthesis* / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide / Q000378:metabolism*; D010902:Pituitary Gland / Q000502:physiology*; D010907:Pituitary Hormones / Q000096:biosynthesis* / Q000235:genetics; D020033:Protein Isoforms; D012313:RNA / Q000737:chemistry / Q000235:genetics; D019105:Random Amplified Polymorphic DNA Technique; D051237:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D015854:Up-Regulation
D029941:Fish Proteins; D006023:Glycoproteins; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D010907:Pituitary Hormones; D020033:Protein Isoforms; D051237:Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide, Type I; C064448:somatolactin protein, fish; D012313:RNA