The initiation of new gene transcription during Xenopus gastrulation requires immediately preceding protein synthesis.

The incubation of Xenopus embryo fragments in cycloheximide at 5 or 10 micrograms ml-1 rapidly inhibits protein synthesis to 10% or less of control levels. In most batches of embryos, treatment with cycloheximide for up to 1 h causes no obvious cellular damage and protein synthesis is fully restored to normal levels 5 h later. Transcript analysis with RNA probes shows that the inhibition of protein synthesis at late blastula or early gastrula stages completely suppresses the normal initiation of actin gene transcription at the mid-late gastrula stage. This applies to muscle-specific actin genes, whose transcription is initiated by induction, as well as to cytoskeletal actin genes not activated by induction. Two-dimensional gel protein analysis shows that cycloheximide irreversibly inhibits only 10% of all genes normally expressed at a postneurula stage and that all of these are genes whose expression is normally initiated during or soon after gastrulation. Cycloheximide treatment causes a limited reduction of DNA synthesis, and no reduction of overall RNA synthesis. We conclude that the initiation of new gene transcription during gastrulation in Xenopus is dependent on the immediately preceding synthesis of certain proteins.