Table 2.
Morphological and biochemical responses to thyroid hormone during amphibian metamorphosis.
| Tissue | Response | |
|---|---|---|
| Morphological | Biochemical | |
| Brain | Restructuring, axon guidance, axon growth, cell proliferation, and death | Cell division, apoptosis, and new protein synthesis |
| Liver | Restructuring, functional differentiation | Induction of urea cycle enzymes and albumin; larval to adult haemoglobin gene switching |
| Eye | Repositioning; new retinal neurones and connections; lens structure | Visual pigment transformation (porphyropsin → rhodopsin); β- crystallin induction |
| Skin | Restructuring; skin granular gland formation; keratinization and hardening; apoptosis | Induction of collagen, 63 kDa (adult) keratin and magainin; induction of collagenase |
| Limb bud, lung | Do novo formation of bone, skin, muscle, nerves, and so forth. | Cell proliferation and differentiation; chondrogenesis |
| Tail, gills | Complete regression | Programmed cell death induction and activation of lytic enzymes (collagenase, nucleases, phosphatases, and matrix metalloproteinases); lysosome proliferation |
| Pancreas, Intestine | Major tissue restructuring | Reprogramming of phenotype, induction of proteases, fatty acid binding protein, and stromelysin-3 |
| Immune system | Redistribution of cell populations | Altered immune system and appearance of new immunocompetent components |
| Muscle | Growth and differentiation; apoptosis | Induction of myosin heavy chain |