Here’s one for the “Dang it, now I have to think about that, too” file. A recent paper suggests that there are mutations in many genetically modified mouse models that could well be confounding their phenotypes. The problem is that so many of these are done from very similar embryonic stem cells and in very similar recipient mouse stains (C57 black!). “Passenger mutations” apparently show up flanking the targeted gene, and they’re not always silent, either.
For instance, it was thought that the gene Casp1 was the principal player that triggered an inflammatory response and cell death pathway in response to foreign organisms, a step involved in lethal shock. That’s because, according to a 1995 study and subsequent work, Casp1 knockout mice did not go into septic shock when challenged with molecules signaling foreign invaders. However, in 2011, researchers at Genentech showed that many Casp1 knockout mice also harbored a mutated Casp11 gene from 129 strain mice. The researchers showed that the passenger mutation to Casp11 was partly responsible for the animals’ resistance to shock.
This result triggered Vanden Berghe and his colleagues to look into their own work with Casp3 knockout mice. They found that their interpretation of Casp3’s role in septic shock had also been confounded by the Casp11 passenger mutation. “It affected two years of work,” Vanden Berghe said.
Here’s a web-based tool this multicenter team has developed to help others search for known mutations of this sort. Definitely worth a look if you’re altering mice for a living!
This gets back to something mentioned here the other day. It’s thought by many that a lot of animal assays are statistically underpowered, especially those from academic labs (where the budgets are tighter). This sort of variable (the new mutational problem) doesn’t help, but there are plenty of others to scatter your data already in a whole animal. That’s particularly true if you’re working in (say) neuroscience, where hard readouts are hard to come by. And the problem is, results in such assays are often the big final readout for a given research program, the test that shows whether the hypothesis was correct or not.
Something to think about next time you see an interesting paper that relies on rodent data. If you’re not a big statistics powerhouse, get someone who is to take a look before you get too wrapped up.