Ma. Stolow et al., GENE-REGULATION BY THYROID-HORMONE DURING AMPHIBIAN METAMORPHOSIS - IMPLICATIONS ON THE ROLE OF CELL-CELL AND CELL-EXTRACELLULAR MATRIX INTERACTIONS, American zoologist, 37(2), 1997, pp. 195-207
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.