Attmepts to analyse the biochemical basis of regional differences in animal eggs.

The microinjection of cell material or macromolecules into living cells is potentially useful for identifying cell components responsible for positional information. Experiments with purified globin mRNA injected into frog oocytes and eggs show that macromolecules can retain their activity when injected into living cells. Experiments with histones show that injected macromolecules can take up their normal intracellular location in living cells. Attempts have been made to identify the molecules involved in regulating DNA synthesis, ribosomal RNA synthesis, and early developmental events by fractionating egg cytoplasm, and by rescuing maternal effect mutants. The present state, and theoretical basis, of such experiments is discussed.