COURTESY OF SU-CHUN ZHANG

Scientists have long been studying the process of how mammalian stem cells differentiate to form specific types of brain cells. Researchers are now reporting another small step toward understanding what conditions are necessary for spinal motor neurons to form: they have coaxed human embryonic stem cells to differentiate into one critical component of the nervous system.

Su-Chun Zhang of the University of Wisconsin-Madison and his colleagues exposed human embryonic stem cells to a variety of growth factors and hormones in sequence in order to encourage them to change into motor neurons. "You need to teach the [embryonic stem cells] to change step by step, where each step has different conditions and a strict window of time," Zhang explains. "Otherwise, it just won't work." The embryonic stems cells first became neural stem cells then changed into the beginnings of motor neurons before finally differentiating into spinal motor neuron cells, the cell type that, in the human body, transmits messages from the brain to the spinal cord. The newly generated motor neurons exhibited electrical activity, the signature action of neurons, and survived in culture for more than three months.

The team next plans to test the cells' ability to communicate with other cell types after they are transplanted into developing chickens. Tests on humans, however, remain years in the future, Zhang cautions. But the findings could still prove useful for people: Zhang posits that motor neuron modeling systems in the laboratory could be used as proxies to screen potential new drugs. The results were published online today by the journal Nature Biotechnology.