Differentiation of Sea Urchin Micromeres: Correlation between Specific Protein Synthesis and Spicule Formation

Sea urchin micromeres were isolated from the 16-cell stage embryos and cultured until they differentiated into spicule-forming cells. Electrophoretic analysis of proteins labeled with [³⁵S]-methionine showed that the differentiation accompanied the synthesis of five cell-specific proteins. These proteins appeared prior to spicule formation and were synthesized continuously or maintained stably while the cultured micromeres formed spicules. In contrast, these proteins were hardly detectable during development of the meso- and macromeres. Correlation between synthesis of the specific proteins and spicule formation was further examined in culture conditions which inhibit spicule formation. In Zn²⁺ -containing or serum-free medium, the micromere descendants failed to form spicules and exhibited markedly reduced synthesis of one of the specific proteins (32 K daltons). After removal of Zn²⁺, or addition of serum, however, spicules were formed with delay but concomitantly with an increase in the synthesis of this protein. This clear correlation suggests the participation of the 32 K protein in the process of spicule formation.