Regional expression of intestinal genes for nutrient absorption.

Leading article Regional expression of intestinal genes for nutrient absorptionMany genes are specifically expressed in the intestine and produce the proteins that digest and absorb the diverse nutrient molecules in the diet.Despite apparent similarities of the mucosa in the duodenum, jejunum, and ileum, these regions differ in their abilities to absorb various nutrients.Clinical awareness of these differences is perhaps most obvious in vitamin B12 malabsorption following terminal ileal disease or resection, but there are many other examples including distal intestinal absorption of bile salts, proximal absorption of calcium and iron, and the various electrolyte transporters that produce net fluid secretion proximally but absorption distally.'These anatomical differences become important in the treatment of patients with the short bowel syndrome where certain, but not all, nutrient systems are capable of adaptation.Recent work is giving a better understanding of the fundamental reasons for these regional variations in gene expression, which are believed to underpin differences in cell and tissue differentiation.This article will review patterns of differentiation in intestinal cells and the control of the expression of nutrient transport genes by specific transcription factors.