John Wallingford admits that he's "kind of terrified" about the complexity of what happens inside cells during development of an organism. But he also admits to having a stubborn streak and he refuses to walk away from a tough scientific problem.
Wallingford, who is on the faculty of the University of Texas at Austin, works on morphogenesis—the process in development whereby an embryo acquires its shape. During the major morphogenetic events—neural tube closure and the vast cellular reorganization known as gastrulation—cells all over the embryo signal back and forth to each other, coordinating the migration routes that will position them to become tissues and organs. When this process goes awry, birth defects can result.
Wallingford has been fascinated by morphogenesis since his undergraduate days at Wesleyan University in the late 1980s when he manipulated frog embryos and used a microscope to watch them develop in a dish of pond water. He soon realized he needed to be able to see what was happening inside these embryos—and their cells—to understand what was going on.
As a graduate student at UT Austin, Wallingford gained a solid background in molecular biology, studying the genes involved in embryonic kidney development. Then, during a pair of simultaneous postdoctoral positions at the University of California, Berkeley and the California Institute of Technology, Wallingford brought those skills in microscopy and molecular biology together to study gastrulation—and, more specifically, a process called convergent extension. This phase of development—in which cells squeeze themselves into a narrow, interconnected column—elongates the body axis and allows the formation of the notochord, the "backbone" of the embryo. Convergent extension is central to gastrulation and key to the proper development of the neural tube that forms the brain and spinal cord.
Wallingford used his molecular biology know-how to identify the genes that power convergent extension and his skills with a microscope—doing time-lapse imaging of gastrulating embryos—to figure out what those genes were doing. He discovered that a set of planar cell polarity (PCP) genes triggers the series of shape-shifting events that drive the elongation of the embryo. That work, published in Nature, was one of three papers on the subject that that came out in 2000. "That kicked off an explosion of work in this area," he says. In a later paper, Wallingford found that the same set of genes governed cell rearrangements that curl a flat sheet of cells in a closed neural tube.
It turns out that the same genes are necessary for spinal cord development in mammals. In mice lacking Dishevelled—the gene that regulates the activity of the other PCP genes—Wallingford and his collaborators found that the hindbrain and spinal cord fail to elongate and therefore fail to close into a tube. What's more, some people with spina bifida have mutations that suppress the activity of PCP genes. "So we may be well placed to make some sort of biomedical contribution to the problem of human birth defects," he notes.
Now Wallingford's lab is trying to figure out how exactly PCP genes direct cell migration during morphogenesis. His work so far suggests that these genes point embryonic cells in the right direction. "But how do cells then act on that information?" he asks. To address that question, in both frogs and mice, Wallingford disrupted genes that take their marching orders from Dishevelled. To his surprise, the resulting mutants look different from animals that lack Dishevelled. For example, mice missing a gene called Fuzzy do not have a properly formed forebrain. The animals also develop extra fingers and toes, suggesting that the genetic network to which PCP genes and their partners belong is "complicated"—Wallingford's way of saying "we just don't get it yet."
Not that that will stop him from trying. Wallingford and his laboratory colleagues work hard every day, although they all break for coffee at 3:00. The informal meetings, at a coffee shop off campus, encourage the exchange of ideas that might otherwise get lost in the day-to-day hustle and bustle of the lab. Besides, Wallingford says, "sometimes you just have to sit down and drink a cup of coffee."