Expression of three distinct somatostatin messenger ribonucleic acids (mRNAs) in goldfish brain: Characterization of the complementary deoxyribonucleic acids, distribution and seasonal variation of the mRNAs, and action of asomatostatin-14 variant

In this study, three somatostatin (SRIF) complementary DNAs (cDNAs) were ch aracterized from goldfish brain. The cDNAs encode three distinct preprosoma tostatins (PSS), designated as PSS-I, PSS-II, and PSS-III. The goldfish PSS -I, PSS-II, and PSS-III contain enzymatic cleavage recognition sites, poten tially yielding SRIF-14 with sequence identical to mammalian SRIF-14, SRIF- 28 with [Glu(1), Tyr(7), Gly(10)]SRIF-14 at its C-terminus, and [Pro(2)]SRI F-14, respectively. The brain distribution of the three SRIF messenger RNAs (mRNAs) were differential but overlapping in the telencephalon, hypothalam us and optic tectum-thalamus regions. Seasonal variations in the levels of the three mRNAs were observed, with differential patterns between the three mRNAs and differences between the sexes. However, only the seasonal altera tion in the levels of the mRNA encoding PSS-I showed close association with the seasonal variation in brain contents of immunoreactive SRIF-14 and inv ersely correlated with the seasonal Variation in serum GH levels described in the previous studies, suggesting that SRIF-14 is involved in the control of the seasonal variation in serum GH levels. The putative SRIF-14 variant , [Pro(2)]SRIF-14, inhibited basal GH secretion from in vitro perifused gol dfish pituitary fragments, with similar potency to SRIF-14; [Pro(2)]SRIF-14 also inhibited stimulated GH release from the pituitary fragments, support ing that [Pro(2)] SRIF-14 is a biologically active form of SRIF in goldfish .