Mar. 18, 2003 COLLEGE STATION, March 17, 2003 – Inside a drawer in Luis Rene Garcia's biology lab, tens of thousands of roundworms are bumping into one another, slithering together and breeding. For the tiny worms, known to science as C. elegans, it's all just another day on a laboratory petri dish. But somewhere in the writhing masses, Dr. Garcia suspects, lie clues to a mystery with large implications: Is some behavior hereditary?
Garcia, an assistant professor of biology at Texas A&M University, is an expert in the sexual habits of C. elegans and the genes that apparently control the behaviors. Although the premise that heredity influences human behavior is controversial, it is more generally accepted in animals, Garcia says, especially when it involves base behaviors such as mating.
He straddles the familiar nature-nurture debate, theorizing that genes set basic tendencies and the environment shapes the behaviors further. To begin testing his hypothesis, Garcia is deconstructing some of the most elemental of all behaviors in one of the world's simplest organisms.
A tiny nematode that lives in dirt and grazes on bacteria, C. elegans is a popular laboratory subject because a scientist can store thousands in a sample dish the size of a hockey puck, easily supplying the numbers necessary for statistically significant experiments. About 1 millimeter long and conveniently transparent, the worm arrives microscope-ready, and even though it has fewer than 400 neurons (compared with hundreds of billions in the human brain) it has a large repertoire of behaviors for a scientist to observe.
Garcia fishes C. elegans from his petri dishes, separates out the males, and alters their genes with mutagenic chemicals. By mutating them, he has discovered that he can short-circuit aspects of their mating behavior. Normally, the little wrigglers do not display aspects of mating behavior until they bump into something they recognize as a mate. But the mutant males that Garcia isolated don't wait for an encounter.
They extend their sex organs spontaneously, trying to mate with a non-existent partner. Such mating gaffes, highly unusual in worms of conventional upbringing, demonstrate an apparent genetic link to the control of behavior, Garcia says.
"Most behaviors are executed in a proper environmental context," he says, suggesting that the genes he disrupted regulate when a behavior should be performed. So far, Garcia has identified four genes that dictate when a C. elegans male should extend its sex organ. Now he is studying the DNA that encodes the genes in hopes of coming to an understanding of how the genes work together to produce the behaviors.
Garcia makes clear that his prime interest is learning how genes influence behavior. But the work has many potential implications – maybe even for medical researchers working to understand Long QT Syndrome, a heart disorder that kills more than 4,000 children and young adults a year.
Garcia has discovered a connection to the roundworm: One of the four C. elegans genes he has identified encodes a protein that is about 66 percent identical to a human protein involved in regulating heart rhythms. Genetic mutations in the human gene can predispose victims of Long QT Syndrome to the spontaneous heart arrhythmias that can kill them without warning. Because the structure of the worm gene is similar to the gene involved in human victims, discovering what mechanism makes the neurons and muscles in the male C. elegans misfire may also explain how the heart misfires in people, Garcia suggested.
Science has far to go, Garcia cautions, before anyone can cure a lethal disease or untangle a thicket as dense as the nature-nurture debate, but some of the answers may be as close as his laboratory drawer.
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