AUTOINDUCTION OF ACTIVIN GENES IN EARLY XENOPUS-EMBRYOS

Activin exhibits a potent mesoderm inducing activity towards the ectod ermal tissue (animal cap) of Xenopus laevis blastulae. Thus in order t o investigate the role of activin in morphogenesis of early Xenopus em bryos, activation of genes for activin beta A and beta B was examined by the reverse transcription polymerase chain reaction. In vivo, activ in beta B mRNA appears to be present in embryonic stage 1 whereas beta A mRNA is undetectable prior to gastrulation. beta B and beta A mRNAs were noted to accumulate after stages 9 and 15 respectively. Activin gene expression in Xenopus animal caps was examined after treatment wi th various concentrations of activin A. Under these treatment conditio ns, both activin beta A and beta B mRNAs accumulated in a dose-depende nt fashion after 24 h. The same effect was noted for treatment with si milar concentrations of activin B. Accumulation of mRNAs was inhibited by the addition of cycloheximide to the culture medium, consistent wi th the proposition that activin gene expression requires certain prote in factors. In total, therefore, these data suggest that an autoinduct ion mechanism is involved in the regulation of activin mRNA levels in normal Xenapus embryos and that this mechanism may play a pivotal role during early embryonic development.