GENE-REGULATION BY THYROID-HORMONE DURING AMPHIBIAN METAMORPHOSIS - IMPLICATIONS ON THE ROLE OF CELL-CELL AND CELL-EXTRACELLULAR MATRIX INTERACTIONS

Amphibian metamorphosis is the developmental process initiated by thyr oid hormone which transforms a tadpole into a frog. This transformatio n requires extensive remodeling of almost every tissue in the animal, One of the more well-studied tadpole tissues that undergoes remodeling is the small intestine, This tissue requires a shortening in length a s well as internal anatomical restructuring to function in the adult f rog, Briefly, the tadpole epithelial cells undergo programmed cell dea th (or apoptosis) and are replaced by a layer of newly formed adult ep ithelium. About 20 thyroid hormone-regulated genes participating in th is intestinal remodeling have been identified, These genes can be divi ded into several groups based on the proposed functions of their produ cts, One of these groups contains several secreted and/or signaling mo lecules, Most prominent among these are the Xenopus homologs of the he dgehog and stromelysin-3 genes, Based on the expression profiles and c ellular localization, hedgehog appears to be involved in adult epithel ial morphogenesis, Stromelysin-3 may participate in basal lamina modif ication which is potentially involved in the apoptosis of the larval e pithelium and development of the adult epithelium. Here we mill review in detail the potential roles for these secreted factors as well as t he proposed molecular mechanisms responsible for their physiological f unctions, Furthermore, me will examine the effect of these proteins on the extracellular environment and how this impacts upon cellular proc esses involved in intestinal remodeling.