Evidence that the ectoderm is the affected germ layer in the wingless mutant chick embryo.

We grafted normal flank ectoderm to the denuded presumptive wing bud mesoderm of stages 14-15 wingless embryos. When this was done, the wingless wing bud mesoderm was capable of inducing a ridge in the grafted ectoderm, maintaining that ridge, and growing out to form a wing. However, when stage 17-18 wingless wing bud mesoderm was combined with a normal leg bud ectodermal jacket, the recombinant bud failed to grow out to form a wing (Zwilling, '56a; and this report). When normal ectoderm was first grafted to a wingless host at stages 14-15, and the resulting stage 18 wing bud was removed and then the mesoderm recombined with a normal ectodermal jacket, the double recombinant bud could form a distally complete wing. However, these wings had some deficiencies compared to similar double recombinants made with normal mesoderm. These results show, first, that the ectoderm is affected by the wingless gene and, second, that there may be a prelimb bud stage interaction between wingless ectoderm and mesoderm such that, by stage 17, the wingless mesoderm becomes defective as a result of the ectodermally expressed mutation. Deficiencies in wingless mesoderm double recombinants indicate that the mesoderm may be sensitive to manipulation, possibly because the ectoderm has affected the mesoderm to some extent before stage 14. We believe it is not possible to determine the affected germ layer in wingless after the limb bud arises. However, after using the prelimb bud recombinant technique which we have designed, it becomes apparent that the ectoderm is affected by the wingless gene.