Increased expression of basement membrane proteins by Smad4 mutant EB outgrowths. A. Day 4 wild-type and Smad4 null EBs grown for 2 days on fibronectin-coated (25 μg/ml) dishes. Smad4 mutant EBs express increased levels of laminin. B. Cryosections of day 4, day 7 and day 10 suspension EBs stained for collagen IV. Smad4 mutant EBs display progressively increased basement membrane deposition beneath the outer endoderm layer.