XENOPUS-LAEVIS TADPOLE LIMB REGENERATION IN-VIVO AND IN-VITRO - THYROXINE DIRECTLY PROMOTES BLASTEMAL CELL-PROLIFERATION AND MORPHOGENESIS

Regeneration in hindlimbs of Xenopus laevis larvae which were amputate d at stage 53 and 55 through the tarsalia region is promoted by thyrox ine (T4), while propyl-thiouracil (PTU) inhibits regeneration when com pared to controls. In this paper, by in vivo and in vitro experiments, we demonstrate that the promoting effect of T4 on the regenerative pr ocesses of larval X. laevis hindlimbs is a direct effect of this hormo ne on the blastemal cells. By contrast, the inhibitory effect of PTU o n the regenerative process is not due to a direct effect on blastemal cells or to a general toxic effect on the treated larvae, but is relat ed to hypothyroidism induced by the drug. We find that: (i) an increas e in blastemal cell proliferation is observed not only in blastemata o f T4-treated larvae, but also in blastemata cultured in vitro in a med ium supplemented with T4; (ii) the renegerative process is accelerated not only in larvae reared in T4 but also in larvae submitted to a com bined treatment of T4 and PTU; (iii) inhibition of cell proliferation is observed in blastemata of PTU-reared larvae but not in blastemata c ultured in vitro in a medium supplemented with PTU. Experiments on thy roidless larvae (which were submitted to transplantation of hindlimbs from larvae at stages 53 and 55 followed by amputation of their own ri ght hindlimb and the transplanted limbs) have shown that without thyro id hormone the regenerative process is arrested at cone stage and the promoting effect of T4 treatment is dependent on limb stage and amputa tion level.