Why do you think your paper is highly cited?

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 (ascidians).

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 all.

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 future?

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 your research?:

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
Professor
Department of Zoology
Kyoto University
Graduate School of Science
Kyoto University
Kyoto, Japan

Keywords: ANCESTRAL VERTEBRATE; GENE DUPLICATIONS; CIONA-INTESTINALIS; NERVOUS-SYSTEM; TELEOST FISH; CHROMOSOMES; REVEALS; ORIGINS; RECONSTRUCTION; INSIGHTS.