Bilateral eye formation in the eyeless mutant Mexican salamander following unilateral, partial excision of neural fold tissues: A quantitative study

Previous results showed that ectopic neural fold grafts, performed unilaterally during neurulation on eyeless mutant axolotl embryos, frequently stimulated eye formation bilaterally. The analysis of the eyeless mutant was expanded in order to obtain quantitative data on the effect of various types of neural fold grafts. While performing these experiments, significant eye formation occurred in controls. Larvae in which neural fold tissues were not grafted but only partially removed at neurula stages formed eyes in some experiments, but not in others. In those cases that eyes did form, partial removal of the posterior neural fold of the prospective ear region stimulated eyes to differentiate more frequently than partial removal of the anterior neural fold of the prospective nose area. In both cases, unilateral neural fold ectomy frequently resulted in bilateral eye formation. There was a positive correlation between the amount of posterior neural fold tissues excised and the frequency of cases in which eyes formed. This increase was roughly 10% if the posterior neural fold excision was performed bilaterally instead of unilaterally. A comparison of eye formation between neural fold excision experiments and ectopic neural fold grafts was performed. There was a statistically significant different between anterior and posterior neural fold operations, but not between grafting and excision experiments. I interpret these results to suggest that there is a signal in the posterior neural fold of the eyeless mutant that prevents eye formation. This signal can be neutralized most efficiently by wounding of the posterior neural folds. In addition, the results provide strong evidence that the effect of wounding propagates from posterior to anterior regions, as well as from one side of the developing neuroepithelium to the other. © 1993 Wiley‐Liss, Inc.