Shedding Some Light

Tuesday, April 22, 2014
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David Plachetzki is an international expert on something most people don’t even know exist—let alone how to pronounce. Spoken with a silent c, the word Cnidaria refers to a phylum of over 10,000 species of animals with gelatinous bodies, including the more commonly known jellyfish and hydra.

Many cnidarians are colonial organisms, meaning there are lots of different individuals physically integrated into one colony. “Think about a coral,” says Plachetzki. “A large coral head will often consist of just a single colony, and all of those little polyps sticking off of it are actually part of a larger whole.” As with coral, it’s possible for Plachetzki to conduct research on cnidarians by picking off a piece of it without killing it. “We can keep animals like cnidarians going in the laboratory for years,” says Plachetzki who keeps cnidarian stocks from which he grafts samples for various research purposes.

“Cnidarians interest me because they are the evolutionary sister group to animals like ourselves. Even though the lineage containing humans and their relatives split from the lineage containing flies and their relatives a very long time ago, the split between the human lineage and that of cnidarians is far older. By studying jellyfish and hydra, we can learn something about our deepest evolutionary ancestors,” says Plachetzki, a new Assistant Professor of Molecular, Cellular, and Biomedical Sciences in the College of Life Sciences and Agriculture (COLSA) at the University of New Hampshire (UNH).

Rare in his specialty, Plachetzki’s research, involving genomics and molecular, cellular, and developmental biology in cnidarians, is already making important contributions to our understanding of complex trait evolution in marine invertebrates. “I’d like to answer questions about how complex animal sensory systems evolved,” says Plachetzki. “Sensory systems of different varieties are present in all sorts of distantly related species. Did this sensory diversity evolve independently in each lineage, perhaps representing novel solutions to similar problems, or, were they passed down through inheritance over the course of animal evolution? Another question we are interested in is how evolution accomplishes all of this tinkering? Does it keep using the same parts, or genes, over and over again to make similar things, or does it fashion new genes for these purposes?” Plachetzki is excited about the practical applications of research in cnidarian biology in informing our understanding of humans and other animals. “From cnidarian research we can make inferences about a very early node in animal evolution,” says Plachetzki. “What is shared between a hydra and a human is most likely to be very important to both species.”

While Plachetzki is best known for his work on visual system evolution in animals, his recent paper on cnidocytes—the stinging cells of cnidarians, used mainly for capturing prey or warding off predators—garnered the 2013 BioMed Central Research Award in Animal Science, Veterinary Research and Zoology, which acknowledges outstanding efforts to support open access to research. “Cnidocytes facilitate both sensory and stinging functions, and are among the most complex types of cells known in animals,” says Plachetzki who has been studying the structural complexity and sensory attributes of these amazing cells.

Plachetzki is building upon more than a century of research on the biology of cnidocytes in hopes of better understanding the specific sensory receptor genes that regulate their function. In his award-winning paper, Plachetzki reports that light regulates cnidocyte stinging function. “It turns out that cnidarian stinging cells use genes related to the human visual pathway to tune their sensitivity to the light environment,” he says. Plachetzki’s research indicates that the harpoon-like stinging cnidocytes don’t discharge toxins through stinging as often when under bright light conditions compared to dim light. These results reveal a previously unknown layer of sensory complexity, responsible, in part, for cnidocyte stinging. “Tuning cnidocyte stingers to the light environment probably has something to do with cnidarian feeding behaviors, which usually occur at dawn and dusk,” says Plachetzki. “One of the coolest things about this research is that it could tell us something about the ancestral function of vision genes, before complex eyes and vision had ever evolved.”

For a big discovery, Plachetzki has been working with a miniscule sample. “In nature, an entire cnidarian colony would be roughly the size of a quarter,” he says. After obtaining a Ph.D. in Ecology, Evolution and Marine Biology in 2009 from the University of California, Santa Barbara, Plachetzki spent four years as a postdoctoral fellow at the Center for Population Biology at the University of California, Davis. He was also the recipient of a prestigious Howard Hughes Medical Institute Fellowship from the Life Sciences Research Foundation. Plachetzki came to UNH last winter as part of a cluster hire for professors with a strong background in genomics. Although this is his first time in New Hampshire, Plachetzki has been traveling to the Eastern seashore for years to collect his cnidarian samples and he is delighted to call New Hampshire home. “One of the reasons I’m excited to be here is that many of the cnidarian species that I work on live locally,” says Plachetzki about the animals of his current research focus.

Plachetzki’s next project is to study a group of cnidarians that can detect self and non-self tissues. “It’s similar to organ rejection in humans,” he says. “Cnidarians use this ability to mediate spatial conflicts in nature. When genetically distinct colonies grow into contact with each other in nature, sometimes they fuse to form one integrated colony while other times they attack one another. How do they make this decision?” Plachetzki asks, knowing this behavior has something to do with genetics and wanting to get to the root of what is responsible.

Plachetzki is conducting research and offering lectures throughout the spring semester, and will begin teaching undergraduate and graduate courses in Genetics and Comparative Genomics beginning this Fall.