This photomicrograph shows Cyanobacteria (green) found
in a common pond. Image source: Wayne Lanier

A billion years ago or so, mitochondria were free living bacteria. Then our ancestors hijacked them and now they do our bidding. And mitochondria aren't the only cells that got hijacked. So did the chloroplast’s ancestors.

Chloroplasts are the part of a plant cell that turns sunshine into sugar. Every green plant that we’ve looked at has them. And chloroplasts were almost certainly once free living cyanobacteria.

Both mitochondria and chloroplasts still have many bacterial qualities including having their own DNA. But they don't have a lot of their old DNA left. Most of it has migrated to where the rest of our DNA is kept—the nucleus. Or at least that's the theory.

Do scientists have any proof that DNA can move in a cell from compartment to compartment? As a matter of fact they do. At least with the chloroplast.

Scientists used their ability to put DNA specifically into a chloroplast or mitochondrion to design an experiment to look for cells where DNA had migrated. What they did was put some DNA into a chloroplast that could only be read in the nucleus. (Remember, chloroplasts and mitochondria are different enough that nuclear DNA doesn't work there and vice versa.)

The DNA they put in made the plant resistant to a poison IF the DNA could be read. One way the plant could survive was if the DNA they put in the chloroplast ended up moving from there to the nucleus. And it did.

In fact, it was pretty common in their experiment. The DNA moved in something like 1 in 16,000 pollen cells. A rate like this suggests that, for example, different cells on the same leaf might have different amounts of chloroplast DNA in their nuclei.

So DNA can move from the chloroplast to the nucleus. And probably from the mitochondrion to the nucleus too. The evidence is less direct for this but there is plenty of DNA in the nuclei of lots of different plants and animals that looks very mitochondrion-like.

This all fits in with our understanding that DNA is not as stable as a lot of people think. DNA changes between generations and within an organism. Chromosomes can get rearranged, genes copied or deleted, small DNA changes can happen and who knows what else. And these changes are a big part of the motor that drives evolution.

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Maybe a clone of this guy will wander the Earth one day.A new study shows that scientists can clone a mouse that has been dead and frozen for 16 years. If they can apply what they've learned to a mammoth that has been dead and frozen for over 10,000 years, then maybe my kids can ride a mammoth one day. Or at least my grandkids can.

You Need More than DNA to Clone

Cloning isn't as simple as was shown in Jurassic Park. You can't take DNA and make a clone from it. Instead, you need an intact nucleus. And ideally, an intact nucleus in an intact cell.

The nucleus is where DNA is kept in our cells. The DNA is stored and packaged there in a way that only Mother Nature can do (for now). We can’t take our 6 feet of DNA and cram it into the tiny space of the nucleus.

Cloning 101.As I said, right now cloning uses intact cells. Here's how it works:

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 it 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

This procedure requires living intact cells to be used. The problem with a frozen animal cell is that it is dead and ice crystals have torn it apart. It is not possible to fuse a beat up dead cell with an enucleated egg.

Cloning Using Frozen Cells

What the researchers in this new study did was change the protocol a bit. Instead of fusing two cells, they harvested nuclei from the frozen cells and injected them directly into the enucleated egg.

When they tried to clone the mouse that had been frozen for 16 years this way, it didn't work. But they managed to get 4 clones by adding an extra step. What they did was to make embryonic stem (ES) cells from the frozen mouse and use those cells to make a clone.

Basically they cloned the mouse but then instead of putting the embryo into a surrogate mother, they harvested its ES cells. Then they used the nuclei from these cells to create a clone in the usual way.

So we can now clone a long frozen mouse. The next step will be to try to clone an extinct animal like a mammoth.

Cloning a Mammoth is Trickier than a Mouse

Mammoth cloning will be no walk in the park. First off, we don’t have any mammoth eggs or cells to use. We'll have to use elephant ones. Hopefully, elephant eggs and/or cells will be compatible with a mammoth's nucleus. ( But there is some concern they they might not be compatible.)

Second, elephants are a lot harder to work with than mice. The experiments in this study used thousands of eggs to get a few clones. I don’t know enough about elephant biology but it seems like you'd need a lot of elephants to get that many eggs.

But this is definitely the first step in resurrecting long dead animals. For now we'll have to focus on the frozen ones. Maybe in the future researchers can figure out how to clone animals stored in formaldehyde. Or from pelts. Then we can start reviving species we humans have managed to kill off over the years.

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