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 a somatostatin-14 variant

In this study, three somatostatin (SRIF) complementary DNAs (cDNAs) were characterized from goldfish brain. The cDNAs encode three distinct preprosomatostatins (PSS), designated as PSS-I, PSS-II, and PSS-III. The goldfish PSS-I, PSS-II, and PSS-III contain enzymatic cleavage recognition sites, potentially 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)]SRIF-14, respectively. The brain distribution of the three SRIF messenger RNAs (mRNAs) were differential but overlapping in the telencephalon, hypothalamus 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 alteration in the levels of the mRNA encoding PSS-I showed close association with the seasonal variation in brain contents of immunoreactive SRIF-14 and inversely 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 goldfish pituitary fragments, with similar potency to SRIF-14; [Pro(2)]SRIF-14 also inhibited stimulated GH release from the pituitary fragments, supporting that [Pro(2)] SRIF-14 is a biologically active form of SRIF in goldfish.