CHANGES IN INSULIN-BINDING CAPACITY OF THE PLASMA-MEMBRANE FRACTION DURING CULTURE IN-VITRO OF CELLS DERIVED FROM MICROMERES OF 16-CELL-STAGE SEA-URCHIN EMBRYOS

In cultured cells derived from isolated micromeres of 16-cell stage se a urchin embryos, which undergo insulin-induced pseudopodial cable gro wth, specific and reversible insulin binding by a 52-kDa protein, prob ably an insulin receptor in the plasma membrane, is augmented during 5 h of culture without any change in the dissociation constant (Kuno et al : 1994). The increase in insulin-binding capacity in micromere-der ived cells was only minimally blocked by actinomycin D and cycloheximi de, which inhibited [U-H-3]uridine incorporation into RNA and [S-35]me thionine incorporation into protein, respectively. Insulin binding cap acity was found in the plasma membrane fraction and the microsome frac tion of isolated micromeres, The capacity in the plasma membrane fract ion increased, accompanied by its decrease in the microsome fraction, during 5 h of culture of micromere-derived cells. The insulin receptor is probably accumulated in microsomes of presumptive micromeres prior to the 16-cell stage and transferred to the plasma membrane, resultin g in an increase in the insulin binding capacity of micromere-derived cells during 5 h of culture.