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.