06.09.2011

The turtle exposes his shell

Over the past few years, Professor Scott Gilbert has put his energy into studying the development and evolution of turtles.

The result has been an abundance of new information, for example, about the mechanisms that guide the development of the turtle's shell and about regularities in developmental biology in general. Scott Gilbert currently works as a FiDiPro Professor on the Viikki Campus of the University of Helsinki.

Finland is a familiar country for Gilbert, a professor from Swarthmore College in the United States. His first research project in Finland was carried out during the years 1990-1991 in Professor Lauri Saxén's laboratory at the University of Helsinki. "It was such an honour to get the opportunity to work with Lauri Saxén. From the 1950s on, Saxén and Sulo Toivonen served as true international pioneers in developmental biology. In terms of research in the field, they created the template by which other researchers work all over the world. In Finland, their work has been successfully carried forward by, among others, Irma Thesleff, Hannu Sariola and Jukka Jernvall, in whose laboratory I'm currently working as a FiDiPro Professor," Gilbert explains. Finland and the Finnish identity are also of interest to Gilbert on the personal level, since his wife's family roots originate in Finland.

"Finnish research in developmental biology has traditionally been of very high standard and forward-looking; it's not complacent - quite the opposite. Researchers in the field are continuously bringing new aspects to the research and not simply relying on existing solutions and methods. Jukka Jernvall is a good example of this. He has introduced new approaches to developmental biology in the form of palaeontology and mathematical modelling. This may open up a totally new and innovative means of examining some of the questions of developmental biology."

The interesting relationship between evolution and development

Scott Gilbert was among the first researchers to create a new field of science, which is now known as evolutionary developmental biology. The birth of this new field of science was enabled by the advance of developmental genetics research, and thereby, the integration of evolution research and developmental biology.

The focus of Gilbert's interest is, in particular, on the mechanisms that guide the development of a turtle's shell. He has been studying turtles for the past decade. "My earlier research focused on the development of the kidneys and the lungs. When many of the large laboratories began to develop interest in the same area, I realised that this signalled a good time for me to change my research focus. I had already, at that point, been writing about the relationship between evolution and development, and I thought that the area held a great deal of interesting projects to research. For instance, how the firefly got its light or how the turtle got its shell."

Gilbert selected the turtle's shell as his focus and achieved quick results. "It was as if we had gone into a garden where no one had been for a hundred years. The fruit was hanging very low on the trees, and we found that there were aspects of the research that were very quickly ready to be published," Gilbert states. "Now, the fruit is a bit higher up and that's one reason why I came back to Finland. I need the well educated personnel and techniques that are found here."

Creatively breaking the rules

Gilbert's research is focused on determining the degree to which the mechanisms that guide the development of the turtle's shell resemble the development of organs in other vertebrates, and whether there have been developmental genetic mechanisms involved in the change of the turtle's shell, such as has been the case in the development of hair, scales and teeth. The results of the research are also expected to shed light on the mechanisms behind bone and epithelial organ illnesses and regeneration. The turtle has become one of the key model animals for evolutionary developmental biology.

According to Gilbert's research, the developmental biology of the turtle is very different when compared to the development of other animals. "We already know that the upper and lower parts of the shell form in completely different ways. The upper part of the turtle shell is formed from its ribs and skin that changes into bone. The plastron (or lower part of the shell) is formed by cells that usually form nerves and pigment. It was surprising to find that the bones of the plastron are very much like the bones of the skull and the face."

"Trunk neural crest cells form the skeleton of the turtle - a process that does not occur in any other species. It appears that the turtle has found a way to creatively break the rules by which all other vertebrates have to abide."
Gilbert believes that this phenomenon is caused by the turtle's neural crest cells having gained a new identity, a process that can be seen as an exceptional developmental trait in the turtle. "There seems to have been a mutation during the development of the turtle that has affected the activity of the genes. Most likely, this all concerns a mutation in a regulatory gene."

Can turtles tell us something about ageing?

At the moment, Scott Gilbert is specifically researching whether the tissue of the plastron (or belly) of the turtle is truly the same as the tissue of a skull. Another project involves the scales of the turtle and their waterproof properties. "The turtle's scales are very different from those of other animals. They don't grow upward or overlap; they grow sideways, along the shell, and they coordinate their growth with the skeleton underneath. This is a beautiful example of coordination of growth, since you can see it both within the whole structure and within each individual part, as magnificent hexagons on the shell."

Gilbert is also intrigued by the long life of turtles. The oldest living species can live for up to 150 years. "Turtle stem cells must be very old since the turtles live so long, so it would be very interesting to study ageing using turtles. As a matter of fact, they don't have ageing syndrome or die of old age, they die primarily from infections, trauma or starvation."

Gilbert is extremely pleased with both the FiDiPro programme and the opportunity to work in Finland. "In the Finnish world of research, everyone is exceptionally well trained and the work ethic is wonderful. Finns value competence, which is apparent in their desire to know how to do things themselves - even when it comes to, for instance, computer programs. This attitude translates well to the area of science and is a sure way to meet with success," Gilbert states.

Text: Riitta Tirronen
Photos: Olli Häkämies

Print