Scientists have identified a sub-type of stem cell responsible for neuron development within the cerebral cortex associated with higher-level brain function. A recent publication in the journal Science suggests
these cells may have been important in the evolution of the human brain and could
boost our understanding of advanced cognition in humans.
Previously all cortical neurons were thought to originate
from the same class of stem cells, known as radial glial cells (RGCs). However,
the study revealed a distinct population of RGCs in mice embryos that gave rise
to upper layer neurons in the outer region of the brain, which is
where higher thinking functions are located. The upper layer is also believed to
be the 'newest' in evolutionary terms.
'Advanced functions like consciousness, thought, and
creativity require a lot of different neuronal cell types and a central
question has been how all this diversity is produced in the cortex', said Dr
Santos Franco of the Scripps Research Institute, California and first author of
the paper. 'Our study shows this diversity already exists in the progenitor
The development process of upper layer neurons was traced in
a specially engineered line of mice. A marker gene, Cux2, known to be expressed
only by upper layer neurons, was linked to a series of genes which glow
fluorescent red when activated.
The scientists could monitor the cells expressing Cux2 under
the microscope, observing that even at the earliest time point in embryonic
brain development, the cells almost exclusively generated upper layer neurons.
Meanwhile, the subgroup of RGCs not expressing Cux2 became lower layer neurons.
The authors conclude that the specific fate of cortical neurons is pre-determined
independent of birth date or location.
Upper layer cortical neurons are especially abundant in the
human brain and these stem cells could in future help provide treatments for
disorders such as schizophrenia and autism. 'This opens a door now to try to
make these neurons, which are frequently affected in psychiatric disorders',
said Professor Ulrich Mueller who led the research team.
But Professor Uta Frith of University College London's Institute
of Cognitive Neuroscience, told the New Scientist: 'There is still a chasm between
neuro-cognitive explanations of autistic symptoms and mechanisms in terms of
cell structure. To put these two levels of explanation together is
a big task'.