N-cadherin is essential for retinoic acid-mediated cardiomyogenic differentiation in mouse embryonic stem cells

Contraction forces developed by cardiomyocytes are transmitted across the plasma membrane through end-to-end connections between the myocytes, called intercalated disks, which enable the coordinated contraction of heart muscle. A component of the intercalated disk, the adherens junction, consists of the cell adhesion molecule, N-cadherin. Embryos lacking N-cadherin die at mid-gestation from cardiovascular abnormalities. We have evaluated the role of N-cadherin in cardiornyogenesis using N-cadherin-null mouse embryonic stem (ES) cells grown as embryoid bodies (EBs) in vitro. Myofibrillogenesis, the spatial orientation of myofibers, and intercellular contacts including desmosomes were normal in N-cadherin-null ES cell-derived cardiomyocytes. The effect of retinoic acid (RA), a stage and dose-dependent cardiogenic factor, was assessed in differentiating ES cells. all-trans (at) RA increased the number of ES cell-derived cardiornyocytes by approximate to 3-fold (at 3x10(-9) M) in wt EBs. However, this effect was lost in N-cadherin-null EBs. In the presence of supplemented at-RA, the emergence of spontaneously beating cardiornyocytes appeared to be delayed and slightly less efficient in N-cadherin-null compared with wt and heterozygous EBs (frequencies of EBs with beating activity at 5 days: 54 +/- 18% vs. 96 +/- 0.5%, and 93 +/- 7%, respectively; peak frequencies of EBs with beating activity: 83 +/- 8% vs. 96 +/- 0.5% and 100%, respectively). In conclusion, cardiomyoyctes differentiating from N-cadherin-null ES cells in vitro show normal myofibrillogenesis and intercellular contacts, but impaired responses to early cardiogenic effects mediated by at-RA. These results suggest that N-cadherin may be essential for RA-induced cardiomyogenesis in mouse ES cells in vitro.