Omitting a step in which stem cells are grown in serum seems to push them toward nerve-cell development, with options
Researchers at the Burnham Institute for Medical Research in La Jolla, Calif., and the University of California at Los Angeles, say they've developed immature nerve cells that are flexible enough to become multiple nervous-system cell types but committed enough not to become other types of cells or form tumors.
Alexey Terskikh at the Burnham Institute, with colleagues there and at UCLA, used two different human embryonic stem cell lines previously approved by the National Institutes of Health to produce "committed neural precursor cells" using a procedure they developed. They say the technique was equally successful in both cell lines.
Their procedure for deriving the partially specialized cells is different from that of other research groups in that they omit a "priming step" in which cells are cultured in serum or serum replacement.
With this new method, the investigators say, the embryonic stem cells rapidly developed into committed neural progenitors, generally after 10 to 14 days in culture.
Unlike neural progenitor cells cultured using certain other conditions, Terskikh's cells appear to have limited proliferation capacity (ability to divide) and instead mature into nerve cells and related cells called glia.
The researchers consider this a good sign, because too much cell division can lead to damaging overproliferation of cells and even result in tumor formation. Tumors have been a concern when considering transplantation of embryo-derived cells into patients.
When the researchers transplanted these neural precursor cells into the brains of mice, they found they migrated to different parts of the brain and took on the characteristics of cells in their surroundings. Importantly, the transplanted human cells didn't overproliferate or form tumors.
The investigators say they've described the molecular stages and pathways that normally occur as embryonic cells develop into nerve cells and have proposed genes that may play a role in the process but have not been previously recognized.
They say their cells can be best described as committed neural progenitor cells, which are on a path to becoming nerve cells but are still capable of becoming different types of nerve cells and don't undergo dangerous proliferation or tumor formation.