Modulation of sarcomere organization during embryonic stem cell-derived cardiomyocyte differentiation

Mouse embryonic stem (ES) cells, when cultivated as embryoid bodies, differ entiate in vitro into cardiomyocytes of ventricles atrium- and pacemaker-li ke cell types characterized by developmentally controlled expression of car diac-specific genes, structural proteins and ion channels, Using this model system, we show here, (1) that during cardiac myofibrillogenesis sarcomeri c proteins are organized in a developmentally regulated manner following th e order: titin (Z-disk), alpha-actinin, myomesin, titin (M-band), myosin he avy chain, alpha-actin, cardiac troponin T and M-protein, recapitulating th e sarcomeric organization in the chicken embryonal heart in vivo. Our data support the view that the formation of I-Z-I complexes is developmentally d elayed with respect to A-band assembly. We show (2) that the process of car diogenic differentiation in vitro is influenced by medium components: Using a culture medium supplemented with glucose, amino acids, vitamins and sele nium ions, we were able to increase the efficiency of cardiac differentiati on of wildtype, as well as of beta(1) integrin-deficient (beta(1)-/-) ES ce lls, and to improve the degree of organization of sarcomeric structures in wild-type and in beta(1)-/- cardiac cells, The data demonstrate the plasticity of cardiogenesis during the differentia tion of wild-type and of genetically modified ES cells.