Incorporation of tritiated cytochalasin B into ectodermal explants of the amphibian gastrula

Ectodermal explants from gastrulae of Triturus alpestris were exposed to tritiated cytochalasin B (5 and 10 mug/ml) for 1/2-2 1/2 h. The flat explants failed to heal into compact spheres and the component cells gradually rounded up. Radioactivity in the fixed and sectioned material was analysed by light and electron microscopic autoradiography. Silver grains were found predominantly over the yolk platelets, but were also scattered over other cellular components. Areas containing pigment granules or the feltwork material, present in the apices of dissociating cells of the superficial layer, exhibited higher activity than areas containing mitochondria or cytoplasmic matrix. Lipid droplets and nuclei showed comparatively little activity. The results are discussed in relation to previous findings on the uptake of tritiated cytochalasin D by cell fractions.