Scientists at Harvard today have published a new report in the journal Cell Stem Cell, showing that ordinary fibroblasts can be directly converted into functioning motor neurons. Starting with easily-accessible mouse fibroblasts, a common cell type found in connective tissue and skin, they added a set of genes that induced generic neuronal specialization, as well as a set of genes specific for a specific nerve type, the spinal motor neuron. The initial combination of eleven genes directly converted the fibroblast cells into specific neuronal cells. In the end, a set of seven genes added to common fibroblast cells was sufficient for direct conversion to functional spinal motor neuron cells. The converted cells not only looked like neurons, but showed a gene expression pattern similar to normal spinal motor neurons, were electrically active like normal nerve cells, and could form connections in the lab dish with muscle cells and stimulate muscle contraction. When injected into developing chicken embryos, the converted cells took up normal residence in the spinal cord.

The group verified that the formation of the spinal motor neurons was due to direct conversion, and did not go through any stem cell intermediate stage. They also showed that human fibroblasts could be directly converted into functional spinal motor neurons using a set of eight neuronal genes. The ability to make specific neurons directly from common adult cells, in an ethical manner, could allow production of patient-specific cells for study of specific motor neuron characteristics, disease susceptibility, and potential drug therapies. There has been a spate of papers showing direct conversion of normal cells to nerve cells. This new paper makes the eighth paper in the last three months. That's a lot of nerve!