Monday, August 4, 2008

Work experience

I'm doing work experience at the National Institute for Medical Research in Mill Hill. It is amazing! I'm not sure how much I can say about it, since it could be dangerous with the animal rights protesters (who are only legally allowed to protest after 6 o'clock on Fridays), so I'm not mentioning any names or anything (I'm afraid I might get it wrong anyway!). Anyway, I was working with a small team who make the genetically modified mice to order. The process itself is interesting; they mate the mice, then harvest the embryos. Then they freeze the eggs using a special process that stops jaggedy ice crystals destroying the embryos. When they need unusual genes, they can insert them into the freshly thawed zygotes. Or, they attach DNA to the outside of sperm and then fertilise the eggs with the coated sperm. Either way, the outcome is the same.
When I got in this morning, the first task was dissection. These big cages of mice were brought in, two brown and one black. All the mice are descended from the House Mouse, but these mice were bred into strains. Basically, you selectively breed the mice into different colours, and then inbreed them to reduce genetic diversity (this helps boost reliability of experiments). As a result, different strains (I'd call them breeds, but you can't always differentiate strains - two mice may look the same, but one might be the "toxic milk" strain, which produces very little zinc in its milk, thus killing all its young. The only reason this strain is still alive is because all the young get "fostered", or the pups are giving zinc supplements.) exhibit different behaviour; the black ones are very skittish and jumpy, whilst the white ones are apparently extremely chilled.
Anyway, the mice are picked up by their tails, and their necks are broken with a plastic wedge thing. Pressure is applied to the back of the neck, and then the front (just to make sure). It's the most humane way, and it's also quite quick. Then, you sort of grip the fur and tear or cut it open, pulling it up over the mouse's head like a jumper. The organs are contained in this little sac - you have to make an incision to get it open as well. There's surprisingly little blood. Anyway, after getting the intestines out of the way, I had to grab the uterus (mice have two), and tug it so the ovary would show itself. After clearing away some tissue (this bit was tricky, I kept dropping the ovary, and one time the oviduct pinged off and ended up in the lungs), you cut out the oviduct, as this is where the zygotes are. I'm quite messy, so I ended up with ovary and uterus on my samples, but if you get really good, you only take the oviduct. You musn't touch the oviduct with the forceps, as this could rupture it, spilling all the embryos all over the place.
After popping the oviducts into a medium to keep hold of it, I watched one person open up the oviduct and get the zygotes under a microscope. The eggs are washed with an enzyme to clear the fuzz of cells around them, and then washed (the enzyme can rupture the egg cells). They're then frozen in these little straw things. I had lunch, then went on to make some hormones using some powder that is worth about £100 per vial (I was really scared I'd spill it!).
Well, toodles for now!

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