Oncogene expression in thymocytes after emetine treatment of mice.

Emetine (33 mg/kg IP) was used as an immunosuppressive agent to inhibit thymic development. The specific and reversible effect of emetine on the macromolecular biosynthesis of thymocytes provided an in vivo model to investigate cellular differentiation. Cortical cells emigrated upon emetine administration at the early stage of inhibition of macromolecular synthesis, followed by a repopulation stage and differentiation 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 rise in total tyrosine kinase activity. The concomitant appearance of an M(r) = 60,000 protein a t = 96 h after emetine treatment may be an indication of the involvement of specific proteins in thymic development.