Transcription of sea-urchin mesenchyme blastula histone genes after heat shock

Turnover of histone acetyl groups during sea urchin early development is not required for histone, heat shock and actin gene transcription

Histone acetylation is an extremely complex, reversible and specific process. In order to evaluate the importance of this modification for gene expression during sea urchin development, acetyl group turnover of histone lysine residues was blocked by sodium butyrate. The continuous presence of 15 Mm sodium butyrate in the incubation medium from the onset of development blocked gastrulation and resulted in chromatin containing hyperacetylated histone molecules in amounts usually not found in nature. At the mesenchyme blastula stage, the expression of the early histone genes was shut off and the expression of the late genes was switched on both in control and sodium butyrate-treated embryos. Investigation of the early histone gene chromatin structure in butyrate-treated embryos revealed a random distribution of nucleosomes when the genes were transcriptionally active as compared to regular nucleosomal packaging when genes were inactive. These changes in chromatin structure during development mimicked the chromatin structural transition of the early histone genes in control embryos. In addition, the ability of heat shock genes to be induced at elevated temperature and repressed at normal temperature was unaffected in butyrate treatment of embryos. Finally, the developmental profiles of the cytoskeletal CyIIIa actin gene expression in control and butyrate-treated embryos were very similar. The data presented suggest that turnover of histone acetyl groups and the overall level of histone acetylation are not determining factors in the up and down regulation of a number of genes during early development of sea urchin.

Processing and nucleo-cytoplasmic transport of histone gene transcripts

Precursors of Xenopus and sea urchin histone mRNAs were synthesized in vitro with the SP6 transcription system, and their maturation and nucleo-cytoplasmic transport was studied by frog oocyte injection. 3' processing is most rapid for homologous histone messenger sequences and does not require either genuine 5' or specific 3' ends of the precursor, but capping of the 5' terminus strongly influences the efficiency of 3' processing. No generation of 5' histone mRNA ends can be detected when precursors containing 5' spacer sequence extensions are injected into the oocyte nucleus. This finding may have some implications for the question whether histone gene transcription could be polycistronic. Using a novel oocyte technique, we have separated nuclei from cytoplasm and have studied the time course of exit of the processed RNA from the oocyte nucleus into the cytoplasm. The results suggest that RNA maturation and nucleo-cytoplasmic transport are not temporally coupled processes.

3' editing of mRNAs: sequence requirements and involvement of a 60-nucleotide RNA in maturation of histone mRNA precursors

In vitro-synthesized transcripts of the sea urchin histone H2A gene with 3' extensions are efficiently and rapidly processed to H2A mRNA with faithful 3' ends in Xenopus laevis oocyte nuclei. Processing requires the presence of a histone-specific dyad symmetry element and of H2A-proximal spacer sequences in the precursor RNA. In DNA injection experiments with a processing-deficient H2A mutant, the transcription products appear to terminate heterogeneously in the first 100-200 base pairs of the post-H2A spacer. Processing of synthetic H3 RNA precursors requires the prior injection of a 60-nucleotide RNA from sea urchin embryos that seems to be a component of a small nuclear ribonucleoprotein.