Histones in Early Embryogenesis: DEVELOPMENTAL ASPECTS OF COMPOSITION AND SYNTHESIS

Abstract

Abstract Acid-soluble proteins were extracted from purified chromatin of eggs, gastrula embryos, and sperm of the sea urchin Arbacia punctulata. The results of disc electrophoresis and amino acid analysis indicate that embryo and sperm extracts resemble mammalian histones whereas acid-soluble proteins from chromatin of unfertilized eggs differ in several respects from mammalian histones. Histones change during development from egg to gastrula from a lysine-rich to a relatively arginine-rich form. Embryos developing in the presence of actinomycin incorporated 14C-valine into cytoplasmic and nuclear proteins at rates similar to those of control embryos during the first 13 hours of development. The specific activity of the cytoplasmic proteins and of nonchromosomal nuclear proteins was about one-fourth that of whole nuclear proteins. These results indicate that chromosomal proteins are the most rapidly synthesized cellular components in early embryogenesis. At least part of this synthesis depends on new mRNA transcribed after fertilization. The incorporation of valine into lysine-rich histones was inhibited by actinomycin, whereas its incorporation into arginine-rich histones was increased 3- to 4-fold by actinomycin. The synthesis of other histone fractions was unaffected by the drug. The facilitated production of certain histone fractions in the presence of actinomycin suggests that normal synthetic rates of embryogenic proteins are maintained in the absence of new mRNA by means of increased production of some proteins, while others are inhibited.