puddingebola sends this excerpt from an article at Science
"Scientists have enabled deaf gerbils to hear again — with the help of transplanted cells that develop into nerves that can transmit auditory information from the ears to the brain. The advance, reported today in Nature, could be the basis for a therapy to treat various kinds of hearing loss. ... Rivolta and his colleagues knew that during embryonic development, a handful of proteins, including fibroblast growth factor (FGF) 3 and 10, are required for ears to form. So they exposed human embryonic stem cells to FGF3 and FGF10. Multiple types of cells formed, including precursor inner-ear hair cells, but they were also able to identify and isolate the cells beginning to differentiate into the desired spiral ganglion neurons. Then, they implanted the neuron precursor cells into the ears of gerbils with damaged ear neurons and followed the animals for 10 weeks. The function of the neurons was restored.'"