The Trichoplax Genome Project
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While Yale University has been a prominent player in the emerging new science of genomics, it may come as a surprise to many that the home of Yale’s first genome project is the Yale Peabody Museum. A collaboration of Curator of Invertebrate Zoology and Department of Ecology & Evolutionary Biology Professor Leo Buss and Professor Steve Dellaporta in the Department of Molecular, Cellular and Developmental Biology has landed Yale funding for genomics-related research and a commitment to sequence the entire genome of a little-known and still largely enigmatic invertebrate, the placozoan Trichoplax adhaerens (below).

 

The Placozoa are free-living metazoans, characterized by a unique body plan. Trichoplax looks superficially like a giant multicellular amoeba, but is in fact a proper multicellular animal with a multinucleate syncytium sandwiched between differentiated dorsal and ventral epithelia. Only 4 distinct cell types exist: monociliated dorsal and ventral epithelial cells, ventral gland cells and syncytial fiber cells. Nerves, sensory cells and muscles are absent and the epithelia lack either a basal membrane or gap junctions. With a top and a bottom, but having neither right and left nor front and back, the Placozoa are without obvious parallel.

Trichoplax was discovered growing on the walls of an aquarium in 1883 by F.E. Schulze, a German scientist who provided a thorough morphological description. While Trichoplax was recognized as distinctive when first described, its status as an outlier became increasingly clear as the bounds of metazoan morphological diversity came to be well known. However, early in the 20th century Schulze’s work was submerged and erroneous reinterpretations of Trichoplax as a hydroid, or even a sponge larva, made their way into textbooks and journal articles. This recasting of Schulze’s results was possible only because no further discovery of the animal itself was reported for over 70 years. Then, in 1969, the noted German protozoologist Karl Grell redis-covered Trichoplax in Red Sea algal samples. Over the next 2 decades Grell and his colleagues systematically investigated several features of the animal’s biology. In the years since, various invertebrate zoologists have collected Trichoplax, but with the exception of the original Grell isolate, there has been no systematic effort to collect and establish new clones in laboratory culture.

Two years ago, Yale students Casey Dunn, Nathan Havill, Ana Signorovitch, Rafe Rosengarten, Melissa Garcia Rice and Professor Leo Buss collected Trichoplax from diverse locations throughout the Caribbean. Signorovitch, Rosengarten and Buss developed a series of new techniques to establish the animal in routine laboratory cultures, and clones from Grenada, Jamaica, Panama and Belize are now maintained continuously. Specimens from these cultures are being accessioned to the Peabody collections. To our knowledge, they are the first specimens of the phylum to be made available for study at any major museum. Working with Dellaporta and Maria Moreno, associate research scientist in the Department of Molecular, Cellular and Developmental Biology, Buss’s group used these animals to generate both small and large insert genomic libraries, which are in turn the raw material from which the entire genome will be characterized. Buss, Dellaporta and Marino have received additional funding to generate the full-length cDNA libraries necessary to produce gene chips for application of Trichoplax to problems of environmental genomics.

Why should such a little-known and curious organism attract the interest of federal genome efforts? What justifies an effort certain to cost many millions of dollars? The reasons are twofold. First, Trichoplax has the smallest genome of any animal yet measured—and by a wide margin. Not only is sequencing relatively inexpensive as a consequence (and the cost-to-benefit ratio correspondingly low), but this tiny genome promises to define, to the extent living organisms allow, the minimal animal gene complement. Second, and most compelling, is the recent demonstration by Dellaporta, using animals produced by Buss’s group, that Trichoplax is unambiguously the most primitive of all animals. Only by sequencing the most primitive animals can we discover those genes that are uniquely “animal” and provide an outgroup for an analysis of their evolution.

Originally published in Yale Environmental News, Spring 2004
vol. 9, no. 2. © 2004 Yale University. All rights reserved.