Molecular cloning and expression of a type-two somatostatin receptor in goldfish brain and pituitary

Somatostatin (SRIF or SS) effects diverse inhibitory actions through bindin g to specific receptors. In this study, a SRIF receptor cDNA was cloned and sequenced fi om goldfish brain using PCR and cDNA library screening. The c DNA encodes a 380-amino acid goldfish type-tno SRIF receptor (designated as sst(2)), with seven putative transmembrane domains (TR;ID) and YANSCANP mo tif in the seventh TMD. a signature sequence for the mammalian SRIF recepto r (sst) family. In addition, the amino acid sequence of the receptor has 61 - 62% homology to mammalian sst(2), 41-47%, homology to other mammalian ss t subtypes and 41-43%;, homology to recently identified fish sst(1) and sst (3) receptors. Both SRIF-14 and [Pro(2)]SRIF-14, two of the native goldfish SRIF forms, but not a putative goldfish SRIF-28, significantly inhibited f orskolin-stimulated adenosine 3':5'-cyclic monophosphate (cAMP) release in COS-7 cells transiently expressing goldfish sst(2), suggesting functional c oupling of the receptor to adenylate cyclase. None of the three peptides af fected inositol phosphate production in the same receptor expression system . Northern blot showed that mRNA for the sst(2) receptor is widely distribu ted in goldfish brain, and highly expressed in the pituitary. The decrease in pituitary sst, mRNA levels following estradiol implantation suggests the presence of a negative feedback mechanism on sst, gene expression. (C) 200 0 Elsevier Science Ireland Ltd. All rights reserved.