Smad4 null embryoid bodies display defects in endoderm migration. A. Day 4 wild-type and Smad4 null EBs were plated onto fibronectin-coated dishes and cultured for 2 days. At both fibronectin concentrations, outgrowth and migration were markedly reduced in Smad4 mutant EBs. B. The surface area of the outgrowths was compared using ImageJ. Smad4 null EB outgrowths, plotted as a percentage of the corresponding wild-type, show a reduction in the total surface area of outgrowth. C. Oct4 staining of EBs grown on 25 μg/ml fibronectin for 2 days. In contrast to barely detectable Oct4 levels in wild-type EB derivatives Smad4 null EBs retain robust expression.