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Building Smarter Mice? Not Sure


The current issue of Cell includes a pair of reports that are getting some attention. Isn't this neat? Or perhaps a bit too easy. A single gene, twice duplicated and degraded as a result of a "copyediting error," is said to be potentially responsible for the superior human intelligence we all enjoy. If you introduce the same error in mice, the same gene (SRGAP2), their brain cells alter the speed of their development and take on shapes more like human ones.

"'Copying' error may have built up our brains," reports MSNBC in a headline that captures the gist of the excited science-media coverage.

A copyediting error appears to be responsible for critical features of the human brain that distinguish us from our closest primate kin, new research finds.

When tested out in mice, researchers found this "error" caused the rodents' brain cells to move into place faster and enabled more connections between brain cells.

In this account, the key duplication accompanied the split of Homo from Australopithecus, according to a statement from Cell:
That's also when the brains of our ancestors began to expand and when dramatic changes in cognitive abilities are likely to have emerged.

The researchers don't think SRGAP2 is solely responsible for that brain expansion, but the genetic interference does have potential benefits. Polleux and colleagues mimic the function of the human-specific SRGAP2 duplication in mice. They show that loss of SRGAP2 function accelerates neurons' migration in the developing brain, potentially helping them reach their final destination more efficiently. Moreover, neurons that have decreased SRGAP2 function, due to expression of the human-specific SRGAP2 display more knob-like extensions or spines on their surfaces, making the neurons appear much more like those found in the human brain. These spines enable connections between neurons to form.

There's a term of art in journalism -- a "ghost" -- that refers to a question the even slightly critical reader naturally wonders about in a story but that the reporter himself never asked; or if he did ask, forgot to include in his story. The ghost in the mouse-brain story is clear: As a result of this minor emendation to their genome, that's supposed to have played a crucial role in our getting smarter, did the mice get any smarter?

Only one account I found, in The New Scientist, actually asked the question and the answer is: No one knows!

Although Polleux and his colleagues have not yet figured out whether the mice were smarter, he says those experiments are in the works.
Oh. In other words, the check is in the mail. If you were thinking about holding your breath on this one, don't.

Photo credit: Ruud Hein/Flickr.