Cell-type specific and thyroid hormone-dependent expression of genes of alpha 1(I) and alpha 2(I) collagen in intestine during amphibian metamorphosis

dBoth the epithelium and the mesenchyme of the larval small intestine of an urans undergoes metamorphic conversion into the adult counterparts. The con version of the mesenchyme has been poorly understood especially at the mole cular level, whereas the changes of the epithelium have been extensively st udied. The present study investigated the metamorphic changes of the mesenc hyme of tadpoles of bullfrog, Rana catesbeiana, focusing on the expression of genes of type I collagen. By using the cDNA clones coding for alpha 1(I) and alpha 2(I) collagen as probes, expression of each collagen gene was ex amined. These genes were drastically up-regulated at the climax period of s pontaneous metamorphosis, which was precociously mimicked by treating tadpo les with thyroid hormone. The increased expression of these genes at the cl imax stage was well correlated with the conversion of the thin larval mesen chyme to more thick and dense adult connective tissues of the intestine. In situ hybridization identified the fibroblasts that were actively expressin g the collagen genes and, therefore, were thought to be responsible for the remodeling. These results strongly suggest that the expression of type I c ollagen genes is regulated during the intestinal remodeling in a cell-type specific and thyroid hormone-dependent manner. (C) 1999 Elsevier Science B. V./International Society of Matrix Biology. All rights reserved.