Macromolecular Syntheses and Nucleocytoplasmic Interactions in Early Development

Abstract

This chapter provides an overview of macromolecular syntheses and nucleocytoplasmic interactions in early development. Many aspects of gene replication, protein synthesis, and mechanisms of gene regulation have been solved by modern molecular biology and studies of viruses and bacteria. The oocyte, the developing fertilized egg, and the embryo raise difficult problems: cytoplasmic heterogeneity may dominate and determine the fate of certain regions, while other phenomena, like regulation, induction, and morphogenetic fields, influence their further destiny. Many hybrid combinations between sea urchins and amphibians are lethal in early stages of development. Biochemical study of such hybrids has supplied a certain amount of information concerning control mechanisms, which are disturbed by the introduction of a foreign nucleus. Methods that provide information about the genetic activity of single cells or clusters of cells are required to analyze the rich heritage left by experimental embryology. The techniques required to demonstrate the activity of the chromatin, that is, its transcriptive capacity, are likely to make rapid progress. The technical problems encumbering detection of tritiated actinomycin, fixation at the ultrastructural level seem to have been vanquished. The condensed and diffused regions of the chromatin differ in their ability to fix actinomycin.