Roles of Matrix Metalloproteinases and ECM Remodeling during Thyroid Hormone-Dependent Intestinal Metamorphosis in Xenopus laevis.

Intestinal metamorphosis in anurans is an excellent model system for studying post-embryonic tissue remodeling and organ development in vertebrates. This process involves degeneration of the larval or tadpole form of its primary functional tissue, the simple tubular epithelium through apoptosis or programmed cell death. Concurrently, adult epithelial stem cells, whose origin remains to be determined, proliferate and differentiate to form a multiply folded, complex adult epithelium. The connective tissue and muscles also develop extensively during this period. Like all other changes during amphibian metamorphosis, intestinal remodeling is controlled by thyroid hormone (TH). Isolation and characterization of genes that are regulated by TH has implicated the involvement of matrix metalloproteinases (MMPs) in the remodeling of the extracellular matrix (ECM) during intestinal metamorphosis. Here we will review some studies, almost exclusively in Xenopus laevis, that support a role of MMPs, particularly stromelysin 3, and ECM remodeling in regulating cell fate and tissue morphogenesis.