Cloning a Mammoth
How Cloning a Frozen Mouse Might Lead to a Cloned Mammoth
The possibility of bringing extinct animals back to life has fascinated people for years. While something like Jurassic Park is unlikely, Pleistocene Park just got one step closer to becoming a reality. One day, mammoths may walk the Earth again.
Many frozen mammoths have been found in Siberia. Some have been so well preserved that people have eaten mammoth steak. So if any animal could be brought back, it seems a well preserved mammoth might fit the bill.
Unfortunately, scientists have never been able to clone using a frozen animal. Until now that is.
In a new study, scientists have cloned a mouse that has been frozen for 16 years. This is a far cry from 16,000 years but is definitely a first step towards cloning a mammoth.
How to Clone an Animal
Scientists need more than DNA to clone an animal. That is why Jurassic Park is so unlikely. The bits of DNA that scientists might get from dinosaur fossils are not good enough to make a dinosaur.
Right now, scientists need an intact nucleus to clone an animal. And ideally, an intact nucleus in an intact cell.
The nucleus is where DNA is kept in cells. The DNA is stored and packaged there in a way that only Mother Nature can do (for now). Scientists don't yet have the skills to take 6 feet of DNA and properly place it into the tiny space of the nucleus.
This is why scientists need at the very least to have an intact nucleus to clone. Here's how cloning is usually done these days:
1) Take a cell from the animal to be cloned
2) Remove the nucleus from an egg (this is called an enucleated egg)
3) Fuse the two cells and let the fused cell divide a few times in a Petri dish
4) Implant the growing embryo into a surrogate mother
5) If everything goes well, a clone is born
The problem with a frozen animal cell is that it is dead and ice crystals have torn it apart. Up until this new study, it has not been possible to fuse a beat up dead cell with an enucleated egg.
Cloning a Frozen Mouse
Researchers got around the problem of frozen cells by changing steps 3 and 4. Instead of fusing two cells, they took nuclei out of the frozen cells and injected them directly into an enucleated egg.
The researchers found that a frozen brain has more intact nuclei than other frozen tissues. The brain has lots of glucose which might make the freezing process gentler.
Injecting a nucleus from a recently frozen mouse into an enucleated mouse egg worked very well. But this method did not work for a mouse that had been frozen for 16 years. The researchers needed to tweak the protocol one more time to clone this mouse.
What they did was to add a nucleus from the long frozen mouse to an enucleated mouse egg and let it grow for awhile in a Petri dish. Then, instead of putting this growing embryo into a surrogate mouse mom, the researchers isolated some embryonic stem (ES) cells from it.
They then fused one of these ES cells to another enucleated mouse egg. When the researchers implanted this embryo into a mouse, they managed to get a clone. In fact, they got a total of four clones.
This means that scientists can clone mice that have been frozen for 16 years. Now they can try to clone a mammoth that has been frozen for 16,000.
Cloning a Mammoth is Trickier than a Mouse
Cloning a mammoth will be hard. Every animal requires a different procedure for cloning. Scientists haven't yet worked out how to clone an elephant let alone a mammoth.
Scientists also don't have any mammoth eggs to use. So they'll have to use elephant ones.
Cloning experiments require lots of eggs because there is so much trial and error in finding the right cloning conditions. The experiments in the mouse study used thousands of eggs. Getting 1000 elephant eggs is much more difficult than 1000 mouse eggs.
There may also be the problem that the eggs are not compatible between mammoths and elephants -- not all eggs work for all animals. However, this may not be that big a problem as elephant and mammoth DNA are pretty similar.
Mammoth DNA is 99.4% Identical to Elephant DNA
In a new study, scientists have managed to figure out about 80% of a mammoth's DNA. In other words, they have figured out the order of around three billion of its A's, G's, C's, and T's.
One of the tricky parts of sequencing long dead animals is contaminating DNA. While an animal has rested somewhere for thousands of years, lots of bacteria, animals, etc., have come and gone in the same spot. All of these beasts leave their DNA behind too.
Then when a scientist comes to read the dead animal's DNA, he or she gets all the other DNA too. This is even a bigger problem than it sounds because there can be a lot more contaminating DNA than there is "interesting" DNA.
In this study, the scientists were able to use DNA from mammoth hair. Hair is tough and any DNA inside is pretty well protected. This means scientists were able to use harsh methods to remove contaminating DNA without damaging the mammoth DNA.
The researchers found that the DNA of a mammoth is pretty closely related to that of a modern day elephant. Much closer than human and chimpanzee DNA, for example.
The researchers found that mammoth and elephant DNA were 99.4% identical. This is actually similar to what has been found so far between humans and Neanderthals.
This similarity makes it much more likely that a mammoth nucleus will be tolerated by an elephant's egg. So it just might be possible to clone a mammoth.
For now scientists will have to keep focusing on frozen dead animals. But who knows what might be possible in the future. Maybe researchers can figure out how to clone animals stored in formaldehyde. Or from pelts. Then maybe humans can start reviving species they have managed to kill off over the years.