Cell culture, quantitative RT-PCR (qPCR), Western blot analyses and immunochemistry were performed according to routine protocols. miR-155 mutant mice and calcineurin transgenic mice (Tg(Myh6-Ppp3ca)37Eno), which were originally generated by Drs. Molkentin and Olson, were obtained from the Jackson lab. The transverse aortic constriction (TAC) operation and measurement of cardiac function by echocardiography are described as described 9 (link).