Cytochalasin B inhibits morphogenetic movement and muscle differentiation of activin-treated ectoderm in Xenopus

Xenopus ectodermal explants (animal caps) begin to elongate after treatment with the mesoderm inducing factor activin A. This phenomenon mimics the co nvergent extension of dorsal mesoderm during gastrulation. To analyze the r elationship between elongation movement and muscle differentiation, animal caps were treated with colchicine, taxol, cytochalasin B and hydroxyurea (H UA)/aphidicolin following activin treatment. Cytochalasin B disrupted the o rganization of actin filaments and inhibited the elongation of the activin- treated explants. Muscle differentiation was also inhibited in these explan ts at the histologic and molecular levels. Colchicine and taxol, which are known to affect microtubule organization, had little effect on elongation o f the activin-treated explants. Go-treatment with HUA and aphidicolin cause d serious damage on the explants and they did not undergo elongation. These results suggest that actin filaments play an important role in the elongat ion movement that leads to muscle differentiation of activin-treated explan ts.