Micromere Differentiation in the Sea Urchin Embryo: Two‐Dimensional Gel Electrophoretic Analysis of Newly Synthesized Proteins

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Abstract
A method for large-scale culture of isolated blastomeres of sea urchin embryos in spinner flasks was developed. Micromeres and meso-, and macromeres isolated from sea urchin embryos at the 16-cell stage were cultured by this method and the patterns of protein synthesis by their descendants were examined by two-dimensional gel electrophoresis of [35S] methionine-labeled proteins. Six distinct proteins with molecular weights of 140-kDa, 105-kDa, 43-kDa, 32-kDa, and 28-kDa (two components) were specifically synthesized by differentiating micromers. Quantitative analysis of the two-dimensional gel patterns demonstrated that all these proteins, except the 32-kDa protein, appeared at the time of ingression of primary mesenchyme cells (PMC''s) in vivo, several hours earlier than the onset of spicule formation. The synthesis of 32-kDa protein was paralleled to active spicule formation and the uptake of Ca2+. Cell-free translation products directed by poly (A)+ RNAs isolated from descendant cells of micromeres and meso-, macromeres were compared by two-dimensional gel electrophoresis. Several spots specific to the micromere lineage were detected. However, none of them comigrated with the proteins synthesized specifically by the cultured micromeres. The results suggest that the expression of these proteins specific to differentiating micromeres may involve post-translational modification.