CELL-INTERACTIONS DURING EARLY SEA-URCHIN DEVELOPMENT

The sea urchin embryo is known to show considerable powers of regulati on. This developmental plasticity has been taken to indicate that many of the early events of determination are a result of cell interaction s. We inquire here whether such interactions do in fact occur during n ormal development, what is their character, and possible mechanisms of these interactions. Attempts from our laboratory to answer these ques tions will be reviewed. Experiments in which marked cells are recombin ed with one another confirm the remarkable plasticity of the animal he misphere cells of these early embryos. The effect of vegetal cells oth er than micromeres is to suppress formation of gut and spicules in ani mal hemisphere cells. Micromeres differentiate into spicules in any lo cation and stimulate animal cells to form gut. Li ion stimulates the f ormation of gut and spicules in cells from the animal hemisphere. Expe riments with phorbol esters and myo-inositol support the idea that the inositol tris phosphate second messenger cycle, acting on protein kin ase C, is a key component of these cell interactions.