Fig. 1. Development of new basolateral domain is contemporaneous with cleavage furrowing. Embryo manually stripped of its vitelline envelope was placed on an agarose-coated surface, incubated briefly with FITC-soybean agglutinin and observed via full-spectrum (upper panels) or epifluorescence (lower panels) illumination. The new membrane domain develops as a broad, unpigmented surface along the cleavage plane (A-D). Lectin bound to the surface of devitellinated egg undergoes local concentration at onset of furrowing (bright stripe, E), followed by appearance and expansion on either side of the new, unlabelled domains of the basolateral membrane (dark areas; arrows). (H) The membrane expansion process repeats during second cleavage (arrows). Note that the new/old membrane boundary corresponds closely to the boundary between pigmented and unpigmented regions. Frames approximately 8 minutes apart.