TREHALASE GENE-EXPRESSION DURING POSTNATAL-DEVELOPMENT OF RABBIT INTESTINE AND KIDNEY - EFFECTS OF GLUCOCORTICOIDS

Rabbit trehalase is a 75-kDa glycosyl phosphatidylinositol-anchored gl ycoprotein of the microvillus membrane of the enterocyte and kidney pr oximal tubule epithelial cells. The purpose of this work was to try to elucidate the molecular basis of trehalase gene expression in intesti ne and kidney during normal postnatal development and after hydrocorti sone injection in suckling rabbits. Trehalase cDNA isolated, sequenced , and characterized by J. Ruf, H. Wacker, P. James, M. Maffia, P. Seil er, G. Galand, A. Kieckebusch, G. Semenza, and N. Mantei (J. Biol. Che m. 265: 15034-15039, 1990) was used to quantify trehalase mRNA. To mea sure the amount of trehalase mRNA encoding for trehalase, poly(A)(+) m RNA was isolated and analyzed by Northern blot hybridization. This cDN A hybridized to a 1.8-kb mRNA in the small intestine and kidney. In de veloping rabbit intestine, after a slow decrease between 4 and 10 days , there is a sharp and parallel rise of both trehalase specific activi ty (28x) and mRNA (10x) between 10 and 30 days after birth. In contras t, in the kidney, between 4 and 30 days, the general developmental pro file of both parameters is very different. There is an overall signifi cant and parallel increase of both trehalase specific activity (3.3x) and mRNA (4.3x). In intestine the longitudinal gradient of trehalase a ctivity and mRNA expression is different in adult and 16-day cortisol- treated suckling rabbits. In intestine, between 10 and 14 days, cortid ol induces a coordinate increase of both trehalase activity (26 x) and mRNA (19x), but at 16 days the two parameters diverge markedly. Daily injections of cortisol between 10 and 16 days do not induce significa ntly trehalase mRNA over controls at 16 days. In only 2 days, between 14 and 16 days, there is a clear loss of trehalase mRNA responsiveness to glucocorticoids. On the contrary, in the kidney, daily injections of cortisol between 10 and 16 days have no significant effect on treha lase mRNA but induce a small and significant increase of trehalase spe cific activity at 16 days (1.8x). Therefore we conclude that, with res pect to the distribution along the small intestine, normal development in kidney and intestine, and after induction with glucocorticoid in i ntestine, alteration in the steady-state levels of trehalase mRNA is a major mechanism for the regulation of trehalase gene expression.