THE 2 NONALLELIC XENOPUS INSULIN GENES ARE EXPRESSED COORDINATELY IN THE ADULT PANCREAS

We have previously shown that the two nonallelic insulin genes in Xenopus laevis are expressed differentially during neurulation in prepancreatic embryos (Shuldiner et al., 1991, Proc. Natl. Acad. Sci. USA 88, 7679-7683). We now examine pancreatic expression with alterations in ambient temperature, glucose administration, fasting and feeding, somatostatin analog treatment, as well as during postmetamorphic growth. Insulin I and II mRNAs were quantitated by slot blot hybridization with specific probes and were expressed as the number of copies (x10(8)) per 5 mu g total RNA +/- SEM. Frogs maintained at 12 degrees showed no significant changes when compared to frogs maintained at 20 degrees. There was a coordinate decrease in insulin I and II mRNA levels in frogs maintained at 29 degrees (Ins I-20, 3.41 +/- 0.34 vs Ins I-29, 2.39 +/- 0.17; Ins II20, 2.59 +/- 0.36 vs Ins II29, 1.67 +/- 0.09; P < 0.05). When compared to fasting animals, both insulin I and II mRNA levels decreased slightly in frogs given repeated intraperitoneal injections of glucose and in those fed ad libitum; there were no changes after a single dose of glucose or in frogs given somatostatin. When compared to young frogs (6 to 24 months), older frogs (36 months) had higher insulin I and II mRNA levels (e.g., Ins I-6mo, 2.14 +/- 0.15 vs Ins I-36mo, 3.68 +/- 0.43; Ins II6mo, 1.21 +/- 0.06 vs Ins II36mo, 3.26 +/- 0.38; P < 0.05). Further, there was a modest reduction in the percentage of insulin I mRNA with aging (e.g., 6 months 63.6 +/- 3.1% vs 36 months 53.9 +/- 2.7%; P < 0.05). We conclude that the two nonallelic insulin genes are regulated coordinately in adult pancreas and suggest that the mechanisms responsible for differential insulin gene expression during neurulation in prepancreatic embryos are distinct from those that regulate coordinate expression in the adult pancreas. (C) 1994 Academic Press, Inc.