SEVERAL CELL RESPONSES TO INSULIN OF CULTURED-CELLS DERIVED FROM MICROMERES, ISOLATED FROM SEA-URCHIN EMBRYOS AT THE 16-CELL STAGE

In micromere-derived cells of sea urchin embryos, treatment with insul in started for up to 24 h during culture at 20 degrees C resulted in a ugmentation of P-32 incorporation into protein (protein phosphorylatio n) followed by activation of P-32 incorporation into RNA (RNA synthesi s) and then induced pseudopodial cable growth, accompanied by consider able decreases in the rates of protein phosphorylation and RNA synthes is. This augmentation of RNA synthesis and cable growth induced by ins ulin were blocked by H-7, which inhibited protein phosphorylation, and were also inhibited by actinomycin D without any inhibition of protei n phosphorylation. Similar results were obtained on treatment with hor se serum, found to contain insulin-like compounds. In cells treated wi th horse serum treated cells, high rates of protein phosphorylation an d RNA synthesis were maintained even after the initiation of cable gro wth and about 5 h later, spicule rods were produced. Insulin treatment did not induce spicule rod formation. In cells treated with horse ser um, actinomycin D treatment started at the time of initiation of cable growth, cables were formed but formation of spicule rods was blocked. These results suggest that horse serum contains some other substance besides insulin-like ones, which induces expression of genes that are indispensable for spicule rod formation.