Membranes and Mating


sabrina_week4_picImagine that you are a bird keeper. You are responsible for making sure that your charges are happy, healthy, and making lots of little baby birdies—but you’re having trouble with that last part. Whether it’s undeveloped eggs or an excess of male births, you need help. Breeding birds isn’t exactly a walk in the park, so who do you call? If you’re a keeper at the San Diego Zoo, you call Dr. Tom Jensen, Ms. Kaitlin Croyle, and Ms. Chelsea Mannie of the Reproductive Physiology Department at the San Diego Zoo Institute for Conservation Research.

Reproductive physiology is basically figuring out how organisms make babies, and it involves a lot of intricate procedures. For instance, several procedures developed by Dr. Jensen and his team involve opening up a fertilized egg without damaging the embryo inside in order to do things like in-ovo sexing, or determining the gender of the egg before hatching. I’m pleased to report that it’s easier to do than it sounds. Ms. Manning, an intern working in the Reproductive Physiology for the California Institute for Regenerative Medicine (CIRM) from CSU San Marcos supervised us as we tried the procedure on chicken eggs. We gently sanded a patch of shell off of our eggs with a sander until the membrane was exposed, which is like a flexible skin between the stuff inside the egg and the shell. The membrane was then gently peeled back to reveal the chicken embryo in all its bizarre glory. I could see the blood flowing—it was so new that it didn’t even have a brain, let alone nerves or eyes. It was in what the scientists at Reproductive Physiology call the “spider” stage, because the embryo’s blood vessels extend out into the yolk like spider legs.

The “spider” stage of development is perfect for the purposes of Dr. Jensen and Ms. Croyle.  The embryo’s blood can be easily accessed without damaging the embryo, and most of its structures—limbs, vital organs, nerves—haven’t developed yet. The blood is particularly important to in-ovo sexing. Blood samples are taken which allow the scientists to know whether it is male or female in twenty-four hours. The Institute has used this process to sex 17 species so far! As you can imagine, it’s pretty nerve-wracking to perform in-ovo sexing on the egg of an endangered species. It’s worth the risk, though, because the earlier the Zoo knows the sex of an animal, the more time they have to figure out how to  proceed with breeding. That’s especially good for endangered species because they need all the help they can get!

That’s not the strangest thing that’s been done for an endangered species, however. Dr. Jensen has been trying to turn chickens into kiwis–a flightless bird from New Zealand! …Sort of. It starts with a type of cell called germ line stem cells, but they’re not the same as the stem cells you hear about in the news. Germ line stem cells can become only two things: more of themselves or sex cells (eggs or sperm). So if the scientists can acquire germ line stem cells from a valuable male kiwi, he can be bred even after his death. But they can’t just produce sperm in the lab. They need a living animal to produce it, and they can’t simply clone this valuable male because, unfortunately, it’s nearly impossible to clone a bird. You know how in mammals, cloning involves replacing the nucleus of an egg with the nucleus of a cell of the individual being cloned? That doesn’t work with birds because the eggs are too big.

So what is the solution? Why, use a chicken, of course! It turns out that when a male bird embryo is in the “spider” stage, its genitals haven’t really formed yet, so its germ line stem cells are still zooming around in the blood. They will settle in the genitals when they develop, but this quirk of development allows Dr. Jensen to inject a few kiwi germ line stem cells into the embryo. This doesn’t hurt it, and it will grow up to become a normal rooster—except for the minor difference of producing kiwi and chicken sperm.

If you want to go into the sciences and do cool things like Dr. Jensen, he says that a good place to start is by choosing good classes and getting good grades in college. Also make sure to do undergrad research, especially if it involves lab work. Go to meetings of people who work in the field you’re interested in. Pester them politely! If they know you, they’ll be more likely to hire you.

Sabrina, Careers Team
Week Four, Winter Session 2014