They plan to use this research to eventually transplant brain cells to treat people with Parkinson's.
The new study, reported in the July issue of Nature Biotechnology, used stem cells from mice.
The researchers, from Harvard Medical School, the Karolinska Institute in Stockholm and elsewhere, gave the stem cells genes that encourage development of dopamine-making cells, and exposed them to other cells called astrocytes that provided chemical signals for proper development.
The results are important but there are some caveats, Dr. Olle Lindvall of the University Hospital in Lund, Sweden, wrote in an accompanying editorial. One is the poor survival after transplantation, which might be overcome.
Another problem is that the source of those cells is problematic. Getting them from aborted fetuses is controversial, and taking cells from animals raises concern about introducing new diseases into people.
Also, human transplantation might require stem cells from people rather than mice.
Finally, Lindvall wrote, it's not clear whether brain cells produced this way would really ease Parkinson's symptoms.