REGULATION OF SUCRASE-ISOMALTASE MESSANGER RNA CONCENTRATION IN RAT SMALL INTESTINE BY SUCROSE FEEDING

Abstract

Sucrose feeding is known to induce increase of sucrase (S) and isomaltase (I) activities. In order to document the molecular process involved, we studied in rat, the regulation of the transcription of the corresponding mRNA in response to sucrose feeding. In this purpose, a cloned rat S-I probe has been prepared. By Northern hybridization in high stringent conditions, the cDNA sequence hybridizes to a single 6kb nucleotides species specific to the rat intestine.

After 3 days of pre-feeding a carbohydrate free diet (cellulose diet, CD), rats were fed either with CD, either with a diet containing high amounts of carbohydrates (sucrose diet, SD). Animals were then killed at 0, lh30, 3h, 6h and 15h after refeeding, and a jejunal segment removed. In the mucosal homogenates, a significant increase in S and I activities (p < 0.05) occured only 3h after initiation of SD. Northern hybridization of equal amount of total jejunal RNA to rat S-I cDNA probe indicated that after lh30 of refeeding, SD rats had twice as much S-I mRNA as those on cellulose diet. This difference in S-I mRNA levels was maintained or increased at tha other experimental times. In contrast, hybridization with β-actin cDNA failed to show difference in the β-actin mRNA.

The rapid production of SI mRNA provides convincing evidence that the carbohydrate stimulated rise of sucrase activity involved an increase of S-I gene expression at the transcriptional level, associated or not with a stabilization of the S-I messenger.

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