Molecular analysis of cardiomyocytes derived from human embryonic stem cells.

During early embryogenesis, the cardiovascular system is the first system to be established and is initiated by a process involving the hypoblastic cells of the primitive endoderm. Human embryonic stem (hES) cells provide a model to investigate the early developmental stages of this system. When removed from their feeder layer, hESC create embryoid bodies (EB) which, when plated, develop areas of beating cells in 21.5% of the EB. These spontaneously contracting cells were demonstrated using histology, immunostaining and reverse transcription-polymerase chain reaction (RT-PCR), to possess morphological and molecular characteristics consistent with cardiomyocytic phenotypes. In addition, the expression pattern of specific cardiomyocytic genes in human EB (hEB) was demonstrated and analyzed for the first time. GATA-4 is the first gene to be expressed in 6-day-old EB. Alpha cardiac actin and atrial natriuretic factor are expressed in older hEB at 10 and 20 days, respectively. Light chain ventricular myosin (MLC-2V) was expressed only in EB with beating areas and its expression increased with time. Alpha heavy chain myosin (alpha-MHC) expression declined in the pulsating hEB with time, in contrast to events in EB derived from mice. We conclude that human embryonic stem cells can provide a useful tool for research on embryogenesis in general and cardiovascular development in particular.