Changes in the Pattern of Intercellular Junctions during Early Embryogenesis of the Starfish, Asterias amurensis

Changes in the cellular adhesion pattern during the early embryogenesis of a starfish Asterias amurensis were examined using carboxyfluorescein (CF) dye as a probe. CF that was injected into one of the blastomeres at the 2- or 4-cell stage was in all cases restricted to the progeny cells of the CF-labelled blastomere. With the advancement of gastrulation, however, the injected dye was distributed not only to the progeny of the labelled blastomere, but also to cells that originated from non-injected blastomeres. At the beginning of mesenchyme cell release, the injected dye spread uniformly to most cells comprising the embryo. When one of the blastomeres situated in the vegetal hemisphere of an 8-cell embryo was labelled, the resulting embryo showed more intense fluorescence in the cells surrounding the archenteron than in the ectodermal layer, suggesting that the cells in ectodermal layer became associated more intimately or earlier than those surrounding the archenteron. Likewise, in double embryos formed by combining two denuded eggs, in which one egg had been labelled with CF, dye spread was observed when the ectodermal layer began to expand. The intercellular spread of CF dye in starfish embryo suggests that there is a dramatic change in the cellular adhesion pattern during the course of gastrulation.