Neurotransmitter specification has been shown to depend on genetic programs and electrical activity; however, target-dependent regulation also plays important roles in neuronal development. We have investigated the impact of muscle targets on transmitter specification in Xenopus spinal neurons using a neuron-muscle coculture system. We find that neuron-muscle contact reduces the number of neurons expressing the noncholinergic transmitters GABA, glycine, and glutamate, while having no effect on the incidence of ChAT expression. We show that muscle activity is necessary for target-dependent reduction of noncholinergic transmitter expression. In addition, we demonstrate that coculture with muscle cells suppresses early spontaneous calcium spike activity in neurons and the presence of muscle cells abolishes activity-dependent transmitter specification. The results indicate that target-dependent regulation can be crucial in establishing neurotransmitter phenotypes and altering early neuronal excitability.

The purpose of this study was to investigate the cardiac‐differentiation potential of induced pluripotent stem cells (iPSCs) generated from human umbilical cord–derived mesenchymal cells. Spontaneous beating colonies were observed at day 7 after the sequential addition of CHIR99021 and IWP‐4. The combined use of CHIR99021 and IWP‐4 downregulated the expression of pluripotency markers while upregulating cardiac transcription factors and cardiomyocyte‐specific markers. The derived cardiomyocytes demonstrated typical sarcomeric structures and action‐potential features; most importantly, the derived cells exhibited responsiveness to β‐adrenergic and muscarinic stimulations. The analyses of molecular, structural, and functional properties revealed that the derived cardiomyocytes were similar to cardiomyocytes derived from BJ foreskin fibroblast cells. In summary, our results demonstrate that functional cardiomyocytes can be generated from human umbilical cord–derived cells. The methodology described here has potential as a means for the production of functional cardiomyocytes from discarded human umbilical cord tissue.

We have previously demonstrated that human umbilical cord-derived mesenchymal stem cells (UC-MSCs) can differentiate into cardiomyocyte-like cells. However, no contracting cells were observed during differentiation. In this study, we generated induced pluripotent stem cells (iPSCs) from UC-MSCs using mRNA reprogramming and focused on the differentiation of reprogrammed iPSCs into functional cardiomyocytes. For cardiac differentiation, the spontaneously contracting cell clusters were present on day 8 of differentiation. Immunostaining studies and cardiac-specific gene expression confirmed the cardiomyocyte phenotype of the differentiated cells. Electrophysiology studies indicated that iPSCs derived from UC-MSCs had a capacity for differentiation into nodal-, atrial-, and ventricular-like phenotypes based on action potential characteristics, and the derived cardiomyocytes exhibited responsiveness to β-adrenergic and muscarinic stimulations. Moreover, the derived cardiomyocytes displayed spontaneous intracellular Ca transients. These results demonstrate that functional cardiomyocytes can be generated from reprogrammed UC-MSCs, and the methodology described here will serve as a useful protocol to obtain functional cardiomyocytes from human mesenchymal stem cells.