Polarization of the Surface Membrane and Cortical Layer of Sea Urchin Blastomeres, and its Inhibition by Cytochalasin B: (post-cleavage surface movements/cortical microfilaments/egg-surface antibody/cytochalasin B/sea-urchin blastomeres).

Sea-urchin blastomeres have two domains of the plasma membrane which can be distinguished immunocytochemically. An egg-surface antibody (anti-ES), which binds to the membrane of the entire surface region of eggs before cleavage, binds to the membrane of the outer surface region of blastomeres after cleavage, but not to that of the cleavage furrow region or interblastomeric surface region. The anti-ES binding sites on the egg membrane were chased after cleavage by labeling the egg plasma membrane with FITC conjugated monovalent anti-ES (FITC-Fab anti-ES) before the first cleavage, and then allowing the eggs to cleave. The surface fluorescence increased in intensity in the cleavage furrow region with progress of furrowing, but after completion of the furrowing, the fluorescence became uniform and finally decreased in the interblastomeric surface region. The distributions of pigment granules and NBD-phallacidin stainable microfilaments in the cortex after completion of furrowing were polarized in the same way as the anti-ES binding area. As cytochalasin B completely inhibited the polarization in both the surface and cortical layer but colchicine did not, polarization of the anti-ES binding area was concluded to be due to the post-cleavage polarized distribution of submembranous microfilaments in the cortical layer.