Fig. 4. Paraxis expression is maintained in both pancreatin- and collagenase-isolated chick PSMs cultured for 6 hours. After 6 hours of culture, control sides (intact halves, A,C) strongly express Paraxis in the anterior PSM in a pattern identical to that of the contralateral isolated PSMs, regardless of whether these were isolated with pancreatin (B) or collagenase (D). Only the collagenase-isolated explants formed somites (asterisks in D). Anterior, top. nt, neural tube; lp, lateral plate; psm, presomitic mesoderm; panc, pancreatin-isolated PSM; coll, collagenase-isolated PSM. Scale bars: 100 µm.