Reversible activation of c-Myc in thymocytes enhances positive selection and induces proliferation and apoptosis in vitro

In order to study the effect of c-Myc activation in T lymphocytes in vivo, we generated transgenic mice that express a 4-hydroxytamoxifen (4-OHT)-depe ndent switchable c-myc oncoprotein under the control of the proximal lck pr omoter. Activation of c-MycER(TM) causes no obvious alteration in T cell on togeny. However, using MHC class I restricted H-Y-TCR transgenic mice, we f ound that c-Myc activation in vivo enhances the efficiency of positive sele ction. Moreover, splenic T cells derived from lck-c-mycER(TM) transgenic mi ce in which c-Myc had been activated exhibited increased proliferation in v itro in response to activation with anti-CD3/CD28 antibody. Activation of c -MycER(TM) also promotes apoptosis in thymocytes in vitro.