Synthesis of ribosomal RNA during sea urchin development. 3. Evidence for an activation of transcription

A denaturation map of sea urchin ribosomal DNA

The ribosomal RNA genes from the sea urchin Lytechinus variegatus have been studied with the electron microsocope using the technique of denaturation mapping. A repeating pattern of denatured regions was found with an average repeat length of 3.87 +/- 0.24 mum. This corresponds to a DNA sequence of approximately 12,000 base pairs with a molecular weight of 8 X 10(6) daltons.

Differential gene activity and segregation of cell lines: an attempt at a molecular interpretation of the primary events of embryonic development

The study of differentiation is concerned with the analysis of the processes responsible for ‘the cellular changes in macromolecular synthesis and composition, patterned in time and space and resulting in specialized functions, forms and organization’ (Moscona, 1973).

The effect of protein synthesis inhibition on the entry of messenger RNA into the cytoplasm of sea urchin embryos

Emetine is a potent inhibitor of protein synthesis in sea urchin embryos. At a concentration of the drug that rapidly inhibits protein synthesis in blastulae by 95%, uridine incorporation into RNA continues for more than 1 hr and presumptive histone messenger RNA is synthesized and transported into the cytoplasm where it is apparently associated with polyribosomes. Possible explanations of this result and its implications for the "informasome" theory of messenger transport in embryonic cells are discussed.

Ribosomal RNA synthesis and the multiple, atypical nucleoli in cleaving embryos

The rate of ribosomal RNA synthesis per nucleus in cleaving sea urchin embryos is similar to the rate at later embryonic stages. The multiple, atypical nucleoli, present in early embryos and usually attributed to decreased ribosomal RNA synthesis, are beginning stages of nucleolar formation. Full nucleolar development requires more time than the brief interphase of the rapidly dividing cells.

Synthesis of RNA in isolated nuclei of sea urchin embryos

It is demonstrated that isolated nuclei of sea urchin embryos are able to incorporate radioactive nucleotides into RNA.Some properties of the incorporation system are described.