Marc Johnson began his research career studying a rabies-like virus in fish. “Working with fish viruses is really cool research,” he notes, but there are just not a lot of people doing it,” and that sense of isolation was eventually too much. In search of collaboration and community, Johnson switched from fish viruses to HIV. Since then, the assistant professor in MU’s Department of Microbiology and Immunology has dedicated his research efforts to the study of these related humans viruses. He and his collaborators have made great progress in understanding how the HIV virus works in order to develop new therapeutics to combat the disease.
Doing maize genetics, according to one geneticist, is “really cool.” It is exactly this kind of enthusiasm that fuels Karen Cone, Professor of Biological Sciences at MU, who specializes in plant genetics. Asked to summarize what researchers in her field actually do, Cone laughs and responds, “Geneticists make mutants…a geneticist learns about the way something works in real life by screwing it up, trying to figure out what’s wrong with the mutant, and then inferring what is normal when the mutant isn’t there.” The mutants that Cone makes involve corn and purple pigmentation.
Dr. Eggert talks about the basics of the work she does, including noninvasive sampling and DNA extraction from those hard samples. She provides some expertly simplified explanations of these complex procedures.
This research on DNA packaging is applicable to every organism, Cone observes. Using the example of a calico cat, she explains: “Tortoise-shell and calico cats have orange and black fur patches on their body. That is due to a DNA packaging phenomenon.” As it turns out, the fur color gene is on the X chromosome. Just as human females have two X chromosomes, so do these calico cats, which are almost always female. In fact, they have one X with an orange-fur gene and one X with a black-fur gene: “so back when that little calico cat, with her different X chromosomes, was a 16 or a 32-cell embryo, in each cell, one of the X chromosomes got really tightly packaged, so tightly that the genes on that chromosome weren’t expressed.” If the X with the orange-fur gene is packaged, she continues, then the X with the black-fur gene remains active. As the cell divides further in the embryo, it will eventually give rise to a black patch of fur. The orange patches, of course, derive from the fact that in another cell, the X with the orange-fur gene, was the one left active, while the black one was balled up too tightly to be expressed. That is one concrete example of how DNA packaging influences whether or not a gene is turned on.
Cone responds to some basic questions about doing genetics research with plants, discussing such matters as reporter genes, gene activity, pigmentation, and the impact of environmental factors on the research.
Cone’s current research seeks to understand the function of a group of genes called chromatin: “Chromatin is the complex of DNA and protein, which allows us as humans–or plants like corn–to pack a lot of DNA into the tiny nucleus of a cell.” The DNA duplex for both corn plants and humans is huge. As she explains, “we have about the same size genome, about three billion base pairs, but ours is really long. We pack about six feet of DNA in every cell,” each of which is only five microns across. That’s a heck of a lot of DNA!” How does all that DNA fit in there? “We’re smart,” suggests Cone, adding that “corn and humans do it the same way,” as does every organism with a nucleus. Therefore, her research on DNA packaging is applicable to every organism, because “from yeast, to mice, to humans, to plants—we all wrap up our DNA basically the same way.” It amounts to a sort of microscopic compressor system, which Cone describes as “amazing.” If researchers can better understand how this chromatin packaging occurs, they might eventually be able to control the process to their advantage.
If researchers can better understand how this DNA packaging occurs, they might eventually be able to control the process to their advantage. As Cone observes, “being able to understand that process might give us a chance down the road to manipulate it, to potentially improve features of the plant for crop production.”
One of Cone’s earlier research projects on corn genetics is the Maize Mapping Project. Funded by the National Science Foundation as part of the Plant Genome Research Program, the project involved a collaboration of investigators at MU, the University of Arizona, and the University of Georgia. Of the four-year project that was completed in 2002, Cone recounts: “Our goal was to make a map of the maize genome.” Using molecular methods and a genetic population tailored specifically for the project, Cone’s research team set about placing DNA “landmarks” onto the chromosomes. “When we finally finished the map,” she says, “there were over 10,000 landmarks on it!”