Raymond Pictet

Control of insulin secretion in the developing pancreatic rudiment.

Abstract The embryonic rat pancreas, removed on the 14th day of gestation and cultivated in vitro , accumulates differentiated levels of exocrine enzymes and insulin. In the period corresponding to days 16–22 in vivo , 99% of the final insulin content accumulates. During this period we have studied the development of competence for insulin secretion, the regulation of this secretion by glucose and other secretatogues, and the rate of synthesis following a secretory challenge. Our results demonstrate that the capacity for insulin secretion develops in parallel with the accumulation of insulin in secretory granules since β granules appear at day 16. On day 16, after 48 hr of culture, both glucose and caffeine are required for detectable insulin secretion. At later stages, insulin release can be effectuated by glucose alone. In the fetal pancreas at day 20 of development, glucose is ten times more efficient than caffeine and fourfold more efficient than caffeine combined with either glucagon, cholera toxin or dibutyryl cyclic AMP. Glucagon, cholera toxin or cyclic AMP in the presence of caffeine increases equally (about tenfold) both the “basal” and the glucose-induced level of secretion. This suggests that glucose and caffeine act independently but synergistically. The integrity of the cells is maintained under the stimulation conditions, and there is a selective increase in insulin synthesis measured during 18 hr following stimulation of insulin release.

Pancreas‐specific genes: Structure and expression

Via recombinant DNA technology the mRNA sequence of pancreatic amylase has been cloned and its nucleotide sequence has been determined. The cloned sequence represents 96% of the total length of amylase mRNA; missing are an estimated 75 ± 30 nucleotides from the 5′ end. The amino acid sequence of rat pancreatic amylase was deduced solely from the nucleotide sequence of the mRNA. Unlike other eukaryotic mRNAs, the amylase mRNA has short 5′ and 3′ untranslated regions, suggesting that long untranslated regions of eukaryotic mRNAs either do not contain extensive functional sequences or that these sequences are incorporated within the amino acid coding region of amylase mRNA. The cloned amylase mRNA sequence was radiolabeled and used as a probe for in situ hybridization. These experiments demonstrate that amylase mRNA is present in all acinar cells but not in other pancreatic cell types. Using the cloned amylase mRNA sequences as a hybridization probe, three nonoverlapping genomic DNA fragments containing amylase gene sequences were isolated. From the similar sequence organization of the three amylase genes visualized by DNA heteroduplex mapping, a consensus structure of a rat amylase gene is proposed. It is an extended gene structure 10 kilobase pairs in length containing the 1547 base pairs of the cloned mRNA coding sequence interrupted by seven intervening sequences ranging from 400–2000 base pairs long. Thus, in nuclear DNA the amylase mRNA coding sequence is disrupted into at least eight segments from 150–300 base pairs long.