|Budget Amount *help
¥3,100,000 (Direct Cost : ¥3,100,000)
Fiscal Year 2004 : ¥800,000 (Direct Cost : ¥800,000)
Fiscal Year 2003 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 2002 : ¥1,600,000 (Direct Cost : ¥1,600,000)
In the digestive tract during amphibian metamorphosis, under the control of the connective tissue, the larval epithelium undergoes apoptosis, whereas a small number of stem cells actively proliferate and form the adult epithelium similar to the mammalian counterpart. We previously examined expression profiles of thyroid hormone(TH) response genes and found that the connective tissue-specific expression of stromelysis-3 (ST3;MMP11) correlates well with the epithelial apoptosis, whereas that of BMP-4 correlates with development of the adult epithelium in the Xenopus laevis intestine. In this study, to clarify molecular mechanisms of the intestinal remodeling, we focused on functions of these TH response genes. First, using transgenic tadpoles expressing ST3 under the control of a heat shock-inducible promoter, we have shown by electron microscopy that the overexpression of ST3 induces apoptosis of the intestinal epithelium possibly through the modification of its basal lamina. Next, we performed organ culture experiments with BMP-4 and its antagonist, Chordin, proteins and have shown that BMP-4 causes precocious differentiation of the adult intestinal epithelium and inhibits cell proliferation of the connective tissue. Finally, to analyze functions of TH response genes more precisely, we established an in vitro gene transfer system by combining electroporation with organ culture techniques. Using this system, we overexpressed one of TH response genes, TH/bZip, in the epithelium of Xenopus tadpole intestines and demonstrated that TH/bZip functions as a growth activator during the intestinal remodeling. This in vitro system may provide a powerful tool for clarifying molecular mechanisms underlying the intestinal remodeling.