Fig. 2.

Muscle and motor neuron cell sources for in vitro models. Myoblasts and motor neurons available for in vitro models fall into three categories: immortalized cell lines, primary cells and pluripotent stem cell derivatives. Immortalized cell lines recapitulate the basic properties of the original cell type and are inexpensive and easy to expand in culture. However, the immortalization process causes de-differentiation and a loss of important structural and functional features. Primary cells are usually the most mature and physiologically relevant cell source but are relatively costly and difficult to obtain, and have a limited ability to expand in culture. Pluripotent stem cells can be widely expanded in culture and then differentiated into myoblasts or motor neurons. Induced pluripotent stem cells have the additional advantage of patient specificity. However, pluripotent stem cell derivatives are generally heterogeneous and immature. hESC, human embryonic stem cell; hiPSC, human induced pluripotent stem cell.