Does phosphatidylinositol 3‐kinase play a role in insulin‐induced outgrowth of pseudopodial cables in cultured cells derived from micromeres of sea urchin embryos?

Cultured cells derived from micromeres isolated from sea urchin embryos at the 16‐cell stage, which have insulin receptors, undergo pseudopodial cable growth and spicule rod formation in culture with horse serum and only cable growth in culture with insulin. Genistein, an inhibitor of protein tyrosine kinase, and wortmannin, an inhibitor of phosphatidylinositol 3‐kinase (PI3kinase), inhibited pseudopodial cable growth in micromere‐derived cells cultured with insulin and also growth accompanied by spicule rod formation in horse serum‐treated cells. The PI3kinase activity in the immunoprecipitates obtained by anti‐phosphotyrosine antibody from the cells cultured with insulin was higher than that in cells cultured without insulin or with insulin and genistein. Following immunoblotting with antibody of SH‐2, Src homology 2 domains in PI3kinase regulatory subunit, a band appeared at 85 kDa in SDS‐PAGE of the immunoprecipitate, obtained from the micromere‐derived cells by anti‐phosphotyrosine antibody. This SDS‐PAGE also showed protein bands at molecular weights similar to IRS‐1 and the insulin receptor β subunit. These indicate that the insulin signal transduction pathway in micromere‐derived cells is somewhat similar to the pathway, in which PI3kinase is involved, in mammalian cells.