Neural-crest derivation of the ossified skull in amphibians revealed by vital labeling with GFP

Derivation of most if not all of the ossified skull from the embryonic neural crest is an accepted axiom of contemporary developmental biology. Yet, this 'fact' is based on direct empirical results involving just one species of vertebrate, the domestic chicken. Anuran amphibians (frogs) pose a particularly difficult challenge in this regard: bone typically forms many weeks after hatching, and tracing individual cells over this lengthy interval is technically difficult. We used RNA encoding for green fluorescent protein (GFP) to label premigratory neural crest in embryos of Xenopus laevis, and assessed cranial derivatives both before and after metamorphosis. Results confirm the neural crest contribution to larval cranial cartilages demonstrated previously by using conventional vital stains, lineage markers, and ablation techniques. They also provide evidence for the neural crest derivation of a major paired skull bone, the frontoparietal; other, later-forming bones are currently under study. This is the first direct empirical demonstration of neural crest contribution to the ossified skull in any amphibian. Supported by NSF.