Nori Satoh talks with
ScienceWatch.com and answers a few questions about
this month's Fast Breaking Paper in the field of
Article Title: The amphioxus genome and the
evolution of the chordate karyotype
Authors: Putnam, NH, et al.
Year: JUN 19 2008
* Dept Energy Joint Genome Inst, Walnut Creek, CA 94598
* Univ Calif Berkeley, Ctr Integrat Genom, Dept Mol &
Cell Biol, Berkeley, CA 94720 USA.
* Univ Oxford, Dept Zool, Oxford OX1 3PS, England.
(addresses have been truncated)
Why do you think your paper is highly
This is because our paper gave clear answers to the long-standing question
of the origin and evolution of chordates.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
Yes, it does. First, the paper provides a kind of conclusion on the origin
of chordates. The chordates consist of urochordates (ascidians),
cephalochordates (amphioxus), and vertebrates.
Although it has been thought that urochordates are mostly primitive, our
paper clearly showed that cephalochordates—but not
urochordates—are basal among the phylum Chordata. This notion
strongly suggests that chordate ancestor(s) are free-living and not sessile
"...our paper clearly showed that
urochordates—are basal among the phylum
In addition, our paper revealed syntenies that are highly coserved between
cephalochordates and vertebrates. This syteny relationship suggests to us
an ancestral chromosome composition of chordates, consisting of 17 linkage
groups. Because the human chromosome composition is better understood when
the cephalochordate chromosomes are duplicated twice, this result also
gives us the strong suggestion that two rounds of genome-wide gene
duplication did occur during the evolution of vertebrates.
How did you become involved in this research, and were
there any problems along the way?
We are interested in the molecular mechanisms involved in the origin and
evolution of chordates. With this aim, Dan Rokhsar and myself, along with
Mike Levine, decoded a urochordate (Ciona intestinalis) genome in
2002. Although this genome project has contributed very much to
establishing Ciona as a model system of developmental genomics, as to the
origin and evolution of chordates, the Ciona genome did not reveal much at
Therefore, soon after the Ciona genome project, we decided to proceed with
the cephlochordate genome project. Because of the comparatively large size
of the cephalochordate genome, it took nearly five years, but we are very
happy to get a wonderful result, quite suggestive as to the evolution of
chordates. Although we had experienced some problems during the Ciona
genome project, this time we have not had as many.
Where do you see your research leading in the
We are now beginning another genome project, namely targeting hemichordates
(Ptychodera flava). If we can do it, we will have much more
genome-wide information on the origin of chordates.
Do you foresee any social or political implications for
The publication of our paper had an impact among ordinary people,
especially children, as amphioxus is highly likely to be among our
vertebrate ancestors. In Japan, numerous media outlets—particularly
newspapers for primary school children—along with TV, radio, and
magazines, publicized this news and the subject of amphioxus became quite a
popular topic of conversation among our citizens.
Dr. Nori Satoh
Department of Zoology
Graduate School of Science