| Abstract: | In gastrulating sea urchin embryos, secondary mesenchyme cells at the tip of the advancing archenteron extend long narrow filopodia which probe the inner surface of the blastocoele wall, rejecting some surface contacts before adhering to other cells. After specific cell adhesions are made, contractions of the filopodia pull the leading tip of the archenteron to the opposite wall of the blastocoele with an accompanying elongation of the archenteron. A study was made of the biochemistry and morphology of the specific adhesions of filopodial extensions by injecting a variety of compounds into the blastocoele of living sea urchin gastrulae and observing their effects on filopodia and cell movements. A number of agents (proteases, lectins) caused specific filopodial detachment and subsequent archenteron regression. Fluorescein-conjugated lectins, including concanavalin A (conA) and wheat germ agglutinin (WGA) exhibited marked specificity of cell surface binding to specific regions (primary mesenchyme cells, blastocoele wall, etc.) of the embryo. |
