Temporal control of gene expression from endogenous and exogenously-introduced DNAs in early embryogenesis of Xenopus...

We review here our studies on temporal control of the expression of genes in zygotic nucleus and of exogenously introduced genes in Xenopus embryos. For zygotic gene expression, our studies have revealed that mRNA synthesis, tRNA synthesis and rRNA synthesis initiates at the cleavage stage, MBT stage and late blastula stage, respectively. We also briefly summarize here results of the effects of weak bases on rDNA expression, nucleo-cytoplasmic transport and polysomal mobilization of newly-synthesized RNAs. For exogenously injected genes expression our data have shown the control of the expression by the promoter and configuration (circular or linear) of the injected DNAs but not necessarily by cellular changes that take place during the midblastula transition (MBT).