Specific Inhibitors of Protein Synthesis Do Not Block RNA Synthesis or Settlement in Larvae of a Marine Gastropod...

Antibiotic inhibitors of protein synthesis were tested for their effectiveness in larvae of the red abalone, Haliotis rufescens (gastropod mollusk). Emetine and anisomycin proved highly effective in this system, while cycloheximide, fusidic acid, puromycin, and tetracycline were less effective. Emetine and anisomycin specifically inhibited protein synthesis but not RNA synthesis. The contribution to protein synthesis by chloramphenicolsensitive prokaryotic contaminants was found to be undetectable, except following the onset of symptoms of toxicity resulting from prolonged exposure to emetine or anisomycin. The induction of larval settlement and plantigrade attachment by γ-aminobutyric acid (GABA), a functional analog of the natural inducer of settlement, occurred even under conditions in which most protein synthesis was inhibited, as expected for a chemosensory system response, whereas subsequent developmental metamorphosis was completely blocked. Because emetine and anisomycin block protein synthesis--including the synthesis of new transcription factors--but do not block early transcription, treatment of marine invertebrate embryos and larvae with these inhibitors can be used to obtain a selective enrichment in the mRNA population of "early gene" transcripts induced directly by GABA and other morphogenetic signals, without dilution by new mRNAs, the appearance of which is dependent on the synthesis of new protein transcription factors.