The main goals of this project are: 1) to evaluate the similarities and differences between human stem cell-derived spinal motor neurons and their fetal counterparts, and 2) to refine the techniques used to make these cells to facilitate motor neuron disease research and create therapeutically beneficial cells. In the second year of this project, we have documented that the initial stages of motor neuron development in stem cell cultures are very similar to the process of motor neuron formation during fetal development. However, stem cell-derived motor neurons appear to be more homogeneous than their fetal counterparts and lack several defining characteristics of mature cells. We are currently investigating the basis of these differences and whether there are any consequences on the function of the stem cell-derived neurons. We have also developed methods for evaluating the communication of stem cell-derived motor neurons with muscle cells. We anticipate that this assay platform will be valuable for modeling the pathology of neurodegenerative diseases that affect motor function. Lastly, we have obtained evidence that the forced expression of genes associated with specific motor neuron groups can strongly influence their trajectory and rate of motor axon growth, and improve innervation of limb muscles.