Evolution of the human brain has always been a topic of
interest for scientists over the years. Many have wondered how human brains
have become so complex and why chimpanzee brains have lagged behind even though
chimpanzees have almost all of the same genes that humans have. Scientists at Duke
University have tackled this question and obtained some interesting results.
More specifically, these scientists have found differences between chimpanzee
and human genetic codes and observed how these differences affected embryonic
brain development in mice.
For the study scientists focused on shorts pieces of DNA
called enhancers that are a part of every genome. These enhancers regulate gene
activity and are sometimes human specific. Until now none of these human
specific enhancers had been shown to influence brain development directly. The scientists searched through chimpanzee
and human genomes to find enhancers that are expressed in brain tissue and
early in development. Enhancers that were largely different between the two
species were of high importance. In the beginning, 106 enhancers were narrowed
down as being potentially important for discovering the differences in chimp
and human brains. Out of these 106, 6 were thought to be involved in brain
development. The enhancers were named HARE1-6, standing for human accelerated
regulatory enhancers. HARE5 showed the
most promise as it is located near a gene, Frizzled8, which is known for its
role in brain development and disease. The researchers directed their attention
onto this enhancer and postulated that it enhanced Frizzled8 since HARE5 and
Frizzled8 make contact in the brain.
The HARE5 in humans and chimpanzees only differ by only 16 base
pairs. However, the human enhancer was active earlier and more active in
general in the mouse embryos than the chimpanzee enhancer. The activity
differences between the two enhancers were detected at a critical time in brain
development. The mouse embryos with the human HARE5 ultimately ended up with
more neurons than those with the chimpanzee HARE5. As the mouse embryos
developed more and more and came closer to the end of gestation the difference
in size of the brains became noticeable. The mice that had human HARE5 had
brains that were 12% larger in area than those that had the chimpanzee HARE5. The
part of the brain that was affected was the neocortex. This part of the brain
is involved in language and reasoning.
This feat was astonishing, just narrowing down the enhancers
in itself was a difficult and cumbersome task. Many other scientists have tried
to do what the Duke University researchers did and failed. As a result of this
successful study, a genetic reason as to why humans have bigger brains than
chimpanzees has been discovered.
I feel that this is so interesting and awesome that it has
finally been discovered. Humans are so closely related to primates, yet so
different. It is interesting to realize that all of the differences are most likely
due to some small change in the genetic code. I mean if just one different
enhancer could make mice brains larger then imagine what a few differences
could amount to. It is astonishing to think about the complexity of genes and how
they work together to produce many different characteristics.
Link to Article: http://www.sciencedaily.com/releases/2015/02/150219133104.htm
Additional Link: http://www.latimes.com/science/sciencenow/la-sci-sn-dna-chimp-human-brains-20150218-story.html
This reminded me of planet of the apes, but in all seriousness finding what differentiates humans and primates down to the base pairs that make up the enhancers is a huge feat. It really is crazy to think small differences in genetic code can really make a huge difference between species.
ReplyDelete