ONCOGENE EXPRESSION IN THYMOCYTES AFTER EMETINE TREATMENT OF MICE

Emetine (33 mg/kg IP) was used as an immunosuppressive agent to inhibi t thymic development. The specific and reversible effect of emetine on the macromolecular biosynthesis of thymocytes provided an in vivo mod el to investigate cellular differentiation. Cortical cells emigrated u pon emetine administration at the early stage of inhibition of macromo lecular synthesis, followed by a repopulation stage and differentiatio n of the thymus. Early events of differentiation were measured by the gene expression of oncogenes showing a gradual decrease of c-myc mRNA level, a temporary decline in c-fos mRNA which was reversed at t = 72 h after emetine treatment. The two-fold increase in mRNA synthesis of c-src oncogene after emetine treatment was paralleled by a fivefold ri se in total tyrosine kinase activity. The concomitant appearance of an M(r) = 60,000 protein at t = 96 h after emetine treatment may be an i ndication of the involvement of specific proteins in thymic developmen t.