For this part of the study, the researchers used stem cells from a microcephalic patient and grew neurons in a culture. They found that in normal brains have progenitor stem cells that make neurons, and can do so repeatedly. In microcephalic brains, the progenitor cells differentiate into neurons earlier, said Madeline A. Lancaster, the study's lead author. The brain doesn't make as many neurons and a child is born with a much smaller brain volume.
Yoshiki Sasai, a stem-cell biologist at the RIKEN Center for Developmental Biology in Kobe, Japan, garnered headlines last year by growing the precursors to a human eye. "The most important advancement is that they combined this self-organization culture with disease-specific cells to model a genetic disease of human brain malformation," he said.
"Everything we have done with other organs starts with this stage," said Anthony Atala, M.D., the director of the Wake Forest Institute for Regenerative Medicine, who has done yeara of research into using 3-D printers to build organs. Atala was not involved in this study, but he noted that before he could build organs he needed to grow the pieces -- to get the cells to differentiate in just the right way. So though it's unlikely anyone will print brains the way he did a kidney, this kind of experiment is where organ regeneration starts.
Knoblich said the next step is studying other brain disorders, but it will take some time to grow enough brain tissue. One factor is maximum size and how far the brain can develop in the culture. Brain cells develop in layers, and there are several by the time a baby is born. The cortical cells Knoblich's team grew only had one such layer. Another factor is getting blood vessels inside the tissue. That problem could be solved sometime in the future, though he said he couldn't predict when.
It is tempting to think one day there will be whole brains in vats, but that isn't likely to happen. "Aside from the severe ethical problem, I do not think this will be possible," Knoblich said. To form actual functioning neural circuits, a brain needs sensory input. "Without any sensory input the proper organization may not happen."
The results of the study appear today in the journal Nature.