Provided are genetically engineered cells comprising a neural stem cell and retroviral expression system in the neural stem cell, which is capable of expressing homeodomain transcription factor Nkx6.1 protein but does not express homeodomain transcription factor Irx3 protein or homeodomain transcription factor Nkx2.2 protein; which is capable of expressing homeodomain transcription factor Nkx6.1 protein and homeodomain transcription factor Irx3 protein; and which is capable of expressing homeodomain transcription factor Nkx2.2 protein or homeodomain transcription factor Nkx2.9 protein. Also provided are methods of generating such genetically engineered motor neurons, V2 neurons, and V3 neurons. Also provided are methods of treating subjects having a motor neuron injury or a motor neuron disease comprising implanting in injured/diseased neural tissue of the subject any of the provided genetically engineered cells, administering to such neural tissue retroviral expression systems which are capable of expressing the appropriate homeodomain protein(s), or transfecting neural stem cells with a retroviral vector, which is capable of expressing the required homeodomain transcription factor protein(s). Provided is a method of determining whether a chemical compound affects the generation of a motor neuron from a neural stem cell.