Sea Lampreys Tell A Tale Of Evolution

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Sea Lampreys Tell a Tale of Evolution

 

By Robert Tindol

 

Among the sea beasts commonly displayed at public aquariums is a rather odd-looking fellow known as a lamprey. Possessing a circular mouth that looks like a suction cup with teeth, lampreys have the distinction of being the most primitive of all creatures with backbones.

 

Biologists from the California Institute of Technology have pinned down a key evolutionary relationship that links lampreys with other vertebrates-including humans.

 

Although lampreys and humans shared their last common ancestor some 560 million years ago, it turns out that the SoxE family of genes is involved in facial development of lampreys during neural crest development, just as SoxE is responsible for formation of the human pharynx and parts of the jaw.

 

In the June 8 issue of Nature, Caltech’s Ruddock Professor of Biology Marianne Bronner-Fraser and David McCauley (now at the University of Oklahoma) show that the role of SoxE in the development of the neural crest reveals new insights into the early evolution of vertebrates.

 

Their work focuses on early embryonic development in lampreys and shows that its facial development is similar to that of the much more evolutionarily advanced zebrafish and frog often used in biological experiments.

 

The reason the findings give new insight into evolutionary biology is that the lamprey is so primitive that it doesn’t actually have a jawbone, as do virtually all other vertebrates.

 

Biologists already knew that SoxE genes were responsible for creation of the neural crest, a transient cell population in the early embryo that leads to the formation of structures such as the peripheral nervous system, and bones and cartilage of the skull.

 

Their discovery that SoxE genes are also involved in the development of lamprey head structures extends the knowledge of the evolution of the face a bit farther back.

 

“We studied lampreys because we are interested in finding out where vertebrates came from,” says Bronner-Fraser.

 

“Lampreys are not necessarily the ideal experimental animal, since they breed only once a year for about a month, but they’re the most primitive vertebrate on Earth today, and therefore are the closest approximation to our common ancestors of 560 million years ago.”

 

Bronner-Fraser and McCauley performed the study by knocking out one of the SoxE genes in one half of the developing lamprey embryo. As a result, the embryos developed into creatures that were normal on one side, but had abnormalities of the pharynx on the other side.

 

The results showed that the SoxE disruption is indeed sufficient to interfere with normal neural crest development, which in turn demonstrates that normal neural crest development in lampreys is dependent on normal SoxE expression.

 

Therefore, the ancestor of lampreys and all other vertebrates had head structures derived from the neural crest. The research also shows that SoxE genes have independent roles in the creation of the mandible and pharynx, and that the neural crest has a crucial role in the proper patterning of the pharynx.

 

In addition to providing new information about the early evolution of life, the Bronner-Fraser lab’s research on the neural crest could lead to eventual treatments of certain congenital defects when the treatment of embryonic problems becomes a reality.