Glowing frogs and the Rockies
Notes from an undergraduate researcher
Posted January 2001
As long as I can remember, frogs and I have always gotten along pretty well. When my sister and I were kids, we shared a few — Droplet, Homera and Sugar — and they outlived our pet hamsters, chameleons and even our irascible cat Spy. So it seemed only natural to me as a biology major to join a frog laboratory in my fourth year at U.Va. And as if studying frog embryonic development for two semesters and a summer were not enough, I had the great fortune to attend the Eighth International Xenopus (Latin: frog) Conference (IXC) in Estes Park, Colo., this past summer.
As exciting as a frog conference may seem to you and me, my friends told me I had hit my all-time low on the coolness scale. Working with frogs for a year is borderline nerdy, they said, but actually flying across the country to convene with other frog-lovers from around the world is a definite entry into the geek zone.
But it depends on whom you ask.
“This year’s conference was extraordinarily energizing — even at 10,000 feet!” said my advisor, Biology Professor Robert M. Grainger, who accompanied three post-doctorate researchers and me to Estes Park, high up in the Rocky Mountains.
“The meeting was a wonderful opportunity for researchers around the world to reveal their often groundbreaking work on how genes control the early stages of embryonic development — turning a ball of undifferentiated cells into a patterned embryo with organs all formed in the right places at the right time,” he said. “For my laboratory it was an especially valuable chance to discuss our new work on frog genetics that we hope will add an important new dimension to our field.”
At the conference, Grainger proudly displayed radiant images of the frog he uses for his research, Xenopus tropicalis. His animal is ideal for genetic experimentation because of its “diploidy” — like humans, it has only two sets of chromosomes. The larger, more traditional Xenopus laevis frog that most of the conference participants and I work on has a comparatively bulky four sets of chromosomes (“tetraploidy”).
In a process called transgenesis, Grainger and other members of his lab have genetically engineered the tropicalis species to endow the normally mud-colored animals with glow-in-the-dark green body parts. For example, to create frogs with green eyes — which populate many tanks in Grainger’s Gilmer Hall laboratory — they must make “designer” DNA called a transgene. A molecular “switch” capable of activating or “turning on” a gene in the frog’s eye is combined with a gene from a jellyfish called Green Fluorescent Protein (GFP).
When the DNA switch activates the eye gene, it also turns on GFP, resulting in transgenic tadpoles that boast glowing green eyes when viewed under an ultraviolet lamp. Hence, the Grainger lab can biochemically study the switches (called “promoters”) that turn genes on and off simply by looking for the glow. This research also sheds some light (no pun intended) upon the process of amphibian development: how the frog egg builds itself into a free-swimming tadpole.
“We can monitor where a given gene is being used by looking for GFP in the living tadpole,” said molecular embryologist Lyle Zimmerman, a member of Grainger’s team. “These things are swimming around, growing, and we can see different genes coming on and doing their thing over time. Before, we could only detect gene activity by doing complicated chemistry, starting by killing and pickling the tadpole.”
Researchers across the globe use frogs to study animal systems because frogs develop in ways similar to humans and allow for testing that is neither permissible, nor in many cases possible, in humans. Future experiments on frogs could involve engineering deficiencies and defects into frog embryos that mimic human diseases in order to better understand the nature of these defects and thereby design better treatments for human maladies. Scientists hope such technology will one day make its way into standard college lab classes and perhaps even high school textbooks.
My frog project, supported by a grant from the 2000 Faculty Senate Harrison Awards, involved mapping prospective brain regions of the frog embryo. Throughout the course of my year with the Grainger lab, I conducted in situ hybridization experiments on the Xenopus laevis embryos to reveal which frog genes visually appeared in particular forebrain, midbrain and hindbrain territories. At the IXC, I presented a poster summarizing this research, and it was a thrill to have my own brain picked by some of the leading minds in the frog world.
Although our schedule for the frog conference listed a panoply of frog talks and frog seminars that ran from 8 a.m. until 10 p.m. for four straight days — enough to make even the most devoted frog-ophile croak — my lab companions and I did manage to find time for a half-day stroll about the scenic, yet touristy, town of Estes Park and to squeeze in a six-mile trek through the Rockies. Accordingly, the next time my friends suggest that my coolness level has reached rock bottom, I’m going to tell them to go take a hike.