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September 2008 -- Yale molecular and evolutionary biologists in collaboration with
Department of Energy scientists produced the full genome sequence of
Trichoplax, one of nature's most primitive multicellular organisms,
providing a new insight into the evolution of all higher animals.
The findings reported in the August 21 online edition of the journal
Nature show that while Trichoplax has one of the smallest nuclear
genomes found in a multi-cellular creature, it contains signature
sequences for gene regulation found in more complex animals and humans.
Further, it defines Trichoplax as a branching point of animal evolution.
"Trichoplax placozoans are animals that have only four body cell
types and no structured organs. They represent descendents of the
oldest multi-celled animal, perhaps older even than sponges," said
author Stephen Dellaporta, professor of molecular, cellular and
developmental biology at Yale.
This study shows that compared with the nuclear genome of humans
that contains 3 billion base pairs, Trichoplax has only 98 million.
Earlier sequencing work showed that the mitochondrial genome of
Trichoplax is over twice the size of those found in most animals with
genes, introns and spacer sequences like the most primitive organisms.
However, size is not all that matters. DNA sequences that organisms
share in common represents what was in their genomes at the time of
their divergence. Unlike other model systems for studying evolution,
including fruit flies and worms, even the arrangement of genes is
conserved between the Trichoplax and human genomes.
"Trichoplax shares over 80 percent of its genes with humans," said
Dellaporta. "We are exited to find that Trichoplax contains shared
pathways and defined regulatory sequences that link these most
primitive ancestors to higher animal species. The Trichoplax genome
will serve as a type of "Rosetta Stone" for understanding the origins
of animal-specific pathways."
Trichoplax is from an ancient lineage and brings significant
insights to understanding how animal life evolved from the common
ancestor 600 million years ago. The consortium believes that the
Trichoplax genome establishes a new standard basal group for the
comparative analysis of animal genomes, genes, and biological processes.
The genome portal for Trichoplax is http://genome.jgi-psf.org/Triad1/Triad1.home.html.
Study co-authors include Mansi Srivastava, Emina Begovic, Jarrod
Chapman, Uffe Hellsten, Takeshi Kawashima, Alan Kuo, Therese Mitros,
Asaf Salamov, Meredith Carpenter, Ana Signorovitch, Maria Moreno, Kai
Kamm, Jane Grimwood, Jeremy Schmutz, Harris Shapiro, Igor Grigoriev,
Leo Buss, Bernd Schierwater, Stephen Dellaporta and Daniel Rokhsar.
Funding for this work was from the Gordon and Betty Moore Foundation,
the National Science Foundation, the German Science Foundation and the
Human Frontiers Science Program.
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