Differentiation of cartilage from cranial neural crest in the axolotl (Ambystoma mexicanum).

Explants of cranial neural crest from neurula-stage Ambystoma mexicanum embryos form cartilage nodules in 10-14 days, when cultured with pharyngeal endoderm. The time course of formation of the nodules, and their appearance, correspond closely to that observed for visceral cartilage in vivo. Endoderm from any area of the sheet surrounding the pharyngeal cavity can induce cartilage formation, but endoderm from regions posterior to the pharyngeal cavity cannot. No other tissues are required for induction in vitro. Cranial neural crest cultured without inductive endoderm did not yield cartilage when taken prior to the stage at which migration begins, indicating that the crest was not determined for cartilage formation at this time. However, a small proportion of the cultures from neural crest taken during the early migratory phase did form cartilage, suggesting that interactions leading to their determination had begun.