What a beauty! This is a mouse embryo, and you can tell that it has been stained for the expression of a gene. But this is not just any gene! This mouse has actually been genetically modified to contain some DNA from the extinct Tasmanian Tiger, Thylacinus cynocephalus.
Now, the point of this genetic modification wasn't to create a half-mouse-half-Tassie-tiger (that would just be absurd. Not to mention impossible...), but rather just to study the function of a particular gene. Because it would be damn near impossible to bring the Tasmanian tiger back from extinction, this approach is the best way to study its genetics.
The Tasmanian tiger
What the scientists did was very carefully extract DNA from four 100-year-old Tasmanian tiger specimens that had been preserved in alcohol, and amplify the DNA of interest (not an easy task if you're working with old DNA!). The DNA they amplified was from a region that controls the expression of a gene called Col2A1. You can think of this DNA as the 'switch' that turns Col2A1 on or off.
They attached the switch to an additional piece of DNA, a 'reporter' gene. Then, they inserted the whole DNA construct into a mouse genome. The reporter gene produces the blue pigment you can see. This method tells us where and when in the embryo the 'switch' is turning on. If the switch is turned on, the reporter gene is active and produces a blue pigment.
Basically, this was a really neat method for studying the function of a gene from an extinct animal! The blue pigment allows us to see where the gene is switched on, and then we can compare that to the mouse version of Col2A1. Turns out, Col2A1 seems to perform the same function whether it's from the Tasmanian tiger or the mouse (its function is in cartilage formation, which is why it is expressed in the forming bones).
This may not be a particularly thrilling conclusion, but the applications of the technique are pretty awesome. For example, maybe one day we could examine what dinosaurs looked like, if we could extract the relevant genes from dinosaurs and insert them into another animal!
And actually, geneticists use this technique for non-extinct animals as well. It's a really good way to figure out if a similar gene performs the same function in different animals. These kinds of studies tell us about the evolutionary history of individual genes, which is bloody interesting, if you ask me.
Reference: Pask, A.J., Behringer, R.R., Renfree, M.B., 2008. Resurrection of DNA Function In Vivo From an Extinct Genome. PLoS ONE, 3(5), e2240.
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