Characterisation of undifferentiated myocardial cells in the embryonic heart post chamber specification

Cardiac progenitor cells (CPC) exist transiently within the cardiac crescent and express Nkx2.5. Recent studies revealed undifferentiated cells within the post-natal heart, although their presence during later embryonic stages is not known. We hypothesize that cardiac progenitor cells exist within later stages of embryonic development and these cells may be identified and characterised based on their expression of Nkx2.5 and lack of expression of cardiac differentiation markers. Nkx2.5+ undifferentiated cells exist within the El 1.5 ventricular myocardium. A novel transgene, Nkx2.5p-EGFP-SVpA-MLC2vp-ECFP-SVpA-ANFp-DsRed-prot.pA, directs EGFP expression to CPC and mature cardiomyocytes and ECFP and/or DsRed expression to mature cardiomyocytes. Nkx2.5+MLC2v-ANF - undifferentiated cells comprise 19%+/-1.378 (n=3; +/-SEM) of the ventricle, differentiate with time and 56% of these cells did not exhibit calcium transients. Therefore, Nkx2.5+ CPCs exist post-chamber specification and are structurally and functionally distinct from mature myocytes. In addition this study highlights a novel tool which can monitor the control of CPC differentiation.