Reaggregation of sea urchin blastula cells: I. Intrinsic differences in the blastula cells

The reaggregation process was studied in dissociated blastula cells from sea urchin embryos to characterize the degree of differentiation among them. During the reaggregation process at least four different cell types appear: (a) cells that remain round, do not reaggregate, and can differentiate into pigment cells; (b) epithelial cells that spread on the substratum and join together to form epithelial sheets, which then develop cilia and round up to form blastulalike structures; (c) spindle-shaped cells that send out protoplasmic extensions over long distances to make contact with other cells; (d) single polyfilamentous cells, their cytoplasm extending into filaments and forming a branched network. The polyfilamentous cells also form syncytia and can show regional differentiation into pigment. Partial success in separating the above types of cells has shown that some of them differ intrinsically. The differences are reflected in morphological differentiation in differential response to calcium, and in amount of hyalin produced.