Chamber‐specific differentiation of Nkx2.5‐positive cardiac precursor cells from murine embryonic stem cells

Embryonic stem (ES) cells are a useful system to study cardiac differentiation in vitro. It has been difficult, however, to track the fates of chamber-specific cardiac lineages, since differentiation is induced within the embryoid body. We have established an in vitro culture system to track Nkx2.5(+) cell lineages during mouse ES cell differentiation by using green fluorescent protein (GFP) as a reporter. Nkx2.5/GFP(+) cardiomyocytes purified from embryoid bodies express sarcomeric tropomyosin and myosin heavy chain and heterogeneously express cardiac troponin I (cTnI), myosin light chain 2v (MLC2v) and atrial natriuretic peptide (ANP). After 4-week culture, GFP(+) cells exhibited electrophysiological characteristics specific to sinoatrial (SA) node, atrial, or ventricular type. Furthermore, we found that administration of 10(-7) M retinoic acid (RA) to embryoid bodies increased the percentage of MLC2v(-)ANP(+) cells; this also increased the expression of atrial-specific genes in the Nkx2.5/GFP(+) fraction, in a time- and dose-dependent fashion. These results suggest that Nkx2.5(+) lineage cells possess the potential to differentiate into various cardiomyocyte cell types and that RA can modify the differentiation potential of Nkx2.5(+) cardiomyocytes at an early stage.