Transient expression of stromelysin-3 mRNA in the amphibian small intestine during metamorphosis

It has been suggested that a matrix metalloproteinase, stromelysin-3 (ST3), is an important enzyme for epithelial transformation; the ST3 gene is known to be regulated by thyroid hormone during Xenopus metamorphosis. In this study, we have examined the distribution of ST3 mRNA in the small intestine of Xenopus during metamorphosis by using in situ hybridization. Around stage 58, ST3 mRNA is first detectable in larval fibroblasts near the muscular layer, and then increases in amount throughout the entire region of connective tissue. By stage 61, when connective tissue cells are rapidly increasing in number, ST3 mRNA is localized in fibroblasts just beneath the epithelium. This localization of ST3 mRNA is in good temporal accordance with modification of the basement membrane and epithelial transformation from the larval to adult form. Thereafter, ST3 mRNA gradually decreases and is no longer detected after stage 63 when the adult epithelium has completely replaced the larval type. The transient expression of ST3 mRNA in the fibroblasts of connective tissue during metamorphosis indicates that it plays an important role in epithelial transformation by changing the basement membrane.