Fractionation and analysis of nuclear proteins in sea urchin embryos

Abstract

Acid-soluble protein from the nuclei of three sea urchin species ( Strongylocentrotus purpuratus, Sphaerechinus granulosus and Paracentrotus lividus) were analyzed during early embryonic development. No histone-like proteins could be detected in unfertilized eggs or in embryos before the blastula stage. Electrophoretic patterns showing five major bands, similar to the mammalian histones, were found for acid-soluble proteins extracted from the blastula nuclei. This pattern did not change qualitatively during further development. There were no differences in histone patterns from the three sea urchin species. Lysine-rich histones from sperm differed electrophoretically from histones in embryos. Electrophoretic patterns of acid-soluble nuclear proteins in unfertilized eggs and embryos before blastula strongly resembled patterns obtained for proteins extracted with acid from cytoplasmic components of the same embryos. The amino acid composition of acid-soluble proteins from unfertilized eggs was not basic. In blastula and especially in gastrula and later stages the amino acid composition of acid-soluble nuclear proteins became basic, resembling the composition of histones from vertebrate nuclei. Nuclear acidic proteins (NaOH-soluble) and nuclear residual proteins increased their content of dicarboxylic amino acids during blastulation. In gastrula and later stages the dicarboxylic amino acid contents of these proteins returned to values seen in unfertilized eggs.