Two-dimensional gel patterns of protein synthesis before and after fertilization of sea urchin eggs

Eggs and embryos of the sea urchin Lytechinus pictus were labeled with [35S]methionine. Aqueous extracts of protein were prepared and analyzed by a high resolution two-dimensional polyacrylamide gel electrophoresis system described recently by O'Farrell utilizing isoelectric focusing and sodium dodecyl sulfate electrophoresis. Out of about 400 distinctly resolved newly synthesized proteins, all but a few detectable in the zygote were being synthesized in the egg. Thus, the activation of translation of stored maternal messenger RNA following fertilization is due to a quantitative rather than qualitative change in the population of messenger RNA available for translation. The patterns of protein synthesis change only slightly during cleavage, but major differences appear by the beginning of gastrulation.