Fig. 5. Critical exposure times to 10 ng/ml FGF2 for chondrogenic differentiation of neural crest cells. Although continuous exposure to FGF2 is not required, the initial 24 hour exposure period is critical in promoting skeletogenic differentiation. The number of cultures containing cartilage nodules after 10 days in vitro is expressed as percentage of the total number of cultures analysed under each experimental condition (indicated above each bar).