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

Abstract

In cultured cells derived from isolated micromeres of 16‐cell stage sea urchin embryos, which undergo insulin‐induced pseudopodial cable growth, specific and reversible insulin binding by a 52‐kDa protein, probably 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‐derived cells was only minimally blocked by actinomycin D and cycloheximide, which inhibited [U‐3H]uridine incorporation into RNA and [35S]methionine incorporation into protein, respectively. Insulin binding capacity was found in the plasma membrane fraction and the microsome fraction of isolated micromeres. The capacity in the plasma membrane fraction 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, resulting in an increase in the insulin binding capacity of micromere‐derived cells during 5 h of culture.