ULTRASTRUCTURAL-STUDY OF INTESTINAL LACTASE GENE-EXPRESSION

The distribution of the mRNA encoding rat intestinal lactase-phlorizin hydrolase (LPH) was analyzed by ultrastructural in situ hybridization , and compared to the distribution of the cognate protein. Different p ictures were obtained depending on the epithelial cell position along the crypt-villus axis: i) cells localized at the crypt base were devoi d of LPH mRNA and protein; ii) cells of the crypt-villus junction and of the villus base showed a high level of mRNA but a low amount of enz yme; and iii) enterocytes of the middle and upper part of the villi ex hibited an intense protein immunolabeling, but a low content of LPH mR NA. The analysis of the intracellular distribution of the LPH mRNA rev ealed a gradient of concentration along the cellular axis, as the tran scripts were the most abundant in the apical and subapical domains of the enterocytes. In addition, LPH mRNA labeling was often paired or ar ranged in a circular shape, suggesting that the transcripts may be loc ated in closed vicinity to rounded structures within the cytoplasm. Th e results indicate that distinct patterns of mRNA and protein occur al ong the villus height during the continuous process of cell differenti ation of the intestinal epithelium. In addition, the emergence of the functional polarity of the enterocytes comes together with the establi shment of an intracellular gradient of concentration of the mRNA encod ing a brush border enzyme. A Link between the intracellular distributi on of LPH mRNA molecules and the membranous flow is proposed.