LENS INDUCTION IN AXOLOTLS - COMPARISON WITH INDUCTIVE SIGNALING MECHANISMS IN XENOPUS-LAEVIS

Amphibian lens induction is an embryonic process whose broad outlines are conserved between anurans and urodeles; however, it has been argue d that some aspects of this process differ significantly between even closely related species. Classical embryologists concluded that in som e species direct contact between the optic vesicle and ectoderm was bo th necessary and sufficient to induce the ectoderm to form a lens, whi le in other species tissues other than the optic vesicle induce lens f ormation. Recent studies of lens induction in Xenopus have argued that lens induction may be more conserved evolutionarily than was previous ly thought and that the different conclusions reached in the classical literature may be due more to experimental methodology than to actual differences in the process of lens induction. We have tested this hyp othesis by examining the timing of lens induction in the axolotl and t he ability of various tissues to induce lenses in explant cultures. We find that, despite the evolutionary divergence between Xenopus and Am bystoma, the mechanism of lens specification is substantially similar in the two species. These results support the hypothesis that the mech anism of lens induction is evolutionarily conserved among amphibians.