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The Journal of Neuroscience, March 21, 2007, 27(12):3069-3077; doi:10.1523/JNEUROSCI.4562-06.2007
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Development/Plasticity/Repair
Functional Neural Development from Human Embryonic Stem Cells: Accelerated Synaptic Activity via Astrocyte Coculture
M. Austin Johnson,1,2,6 Jason P. Weick,6 Robert A. Pearce,1,5 andSu-Chun Zhang1,3,4,6,7 1Neuroscience Training Program, 2Medical Scientist Training Program, Departments of 3Anatomy, 4Neurology, and 5Anesthesiology, School of Medicine and Public Health, 6Waisman Center, and 7WiCell Institute, University of Wisconsin, Madison, Wisconsin 53705
Correspondence should be addressed to Dr. Su-Chun Zhang, Waisman Center, University of Wisconsin, 1500 Highland Avenue, Madison, WI 53705. Email: Zhang{at}waisman.wisc.edu
How a naive human neuroepithelial cell becomes an electrophysiologically active neuron remains unknown. Here, we describe the early physiological development of neurons differentiating from naive human embryonic stem (hES) cells. We found that differentiating neuronal cells progressively decrease their resting membrane potential, gain characteristic Na+ and K+ currents, and fire mature action potentials by 7 weeks of differentiation. This is similar to the maturation pattern observed in animals, albeit on a greatly expanded time scale. An additional 3 weeks of differentiation resulted in neurons that could fire repetitive trains of action potentials in response to depolarizing current pulses. The onset of spontaneous synaptic activity also occurred after 7 weeks of differentiation, in association with the differentiation of astrocytes within the culture. Cocultures of hES cell-derived neuroepithelial cells with exogenous astrocytes significantly accelerated the onset of synaptic currents but did not alter action potential generation. These findings suggest that the development of membrane characteristics and action potentials depend on the intrinsic maturation of Na+ and K+ currents, whereas synaptic transmission is enhanced by astrocytes, which may be achieved independently of the maturation of action potentials. Furthermore, we found that although astrocyte-conditioned medium accelerated synaptic protein localization, it did not increase synaptic activity, suggesting a contact-dependant mechanism by which astrocytes augment synaptic activity. These results lay the foundation for future studies examining the functional development of human neurons and provide support for the potential application of human cells in restorative neuronal therapies.
Key words: electrophysiology; action potential; forebrain; glia; neuronal progenitor cell; synaptic communication
Received Oct. 20, 2006; revised Jan. 11, 2007; accepted Feb. 6, 2007.
Correspondence should be addressed to Dr. Su-Chun Zhang, Waisman Center, University of Wisconsin, 1500 Highland Avenue, Madison, WI 53705. Email: Zhang{at}waisman.wisc.edu
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