While pluripotent stem cells, such as iPS cells, can be made into all cells in the human body, scientists are struggling to make several cell types efficiently. Complicated protocols that require advanced skills and last several weeks or months are often needed. That is the case for motor neurons, the cell intensively studied by the Haruhisa Inoue lab.

"We want a protocol that generates motor neurons fast and easily," said Professor Inoue.

In recent years, a number of laboratories have reported protocols for the differentiation of motor neurons using small molecules. "The preparation of the motor neurons requires many steps with small molecules," explains neurologist Kazuya Goto, a Ph.D. student in the Inoue lab. "We thought using transcription factors could simplify the method." Goto reports this method in a newly published paper.

Three transcription factors are known to be crucial for the induction of motor neurons from iPS cells, Lhx3, Ngn2 and Isl1. Goto encapsulated these factors into a single Sendai vector that he then transduced into iPS cells.

"We detected a marker for motor neurons in just two days," he said, a period much shorter than other protocols. The method also led to more than 90% of the transduced iPS cells becoming motor neurons, far above the levels reported previously. "The single vector is why this method was so effective," he said, adding, "Because we put all three transcription factors into one vector, we got such high homogeneity."

The speed and purity are key for investigating related diseases like ALS, which causes a severe loss of motor neurons. "We could make motor neurons from ALS patient iPS cells. These cells showed the disease phenotype," said Goto.

Inoue is very excited about the protocol, because he believes it will make stem cell research more accessible to scientists studying motor neuron diseases. "It is a very simple method. Anyone with basic molecular biology skills should be able to make motor neurons using it," he said.

• http://dx.doi.org/10.1016/j.omtm.2016.12.007