Fundamental structure of vertebrate species is found in pharyngulae on the course of early development. To know how this structure is established, we study morphogenesis of amphibians in terms of ontogeny and phylogeny.
Research contentHow the vertebrate morphology is established in terms of ontogeny and phylogeny?
Our long-term goal is to understand how the morphological structure of vertebrate is established. To reach the goal, we study two developmental processes, one is the gastrulation movement and the other is the neural crest formation. Though size and shape of eggs are quite different, and manner of cell division after fertilization is also different in vertebrate species, body shape of pharyngulae are known to look similar. This similarity is generated during gastrulation. That is why we think the gastrulation is one of the most important processes for the vertebrate development. The neural crest is thought to be the fourth germ layer, which can generate most of the vertebrate head structures. The neural crest is found only in vertebrate species. So vertebrate species are said to be defined by possession of the neural crest. Therefore we think that to resolve how the neural crest arose in phylogeny is to understand, in part, how vertebrate is established in evolution. For that purpose we study how neural the crest is generated in terms of ontogeny.
What is the nature of vertebrate gastrulation?
We are now working mainly with Japanese newt and also with Xenopus laevis. We found the gastrulation process of Xenopus was totally different from that written in the textbook (Koide, T., Umesono, K. and Hashimoto, C. (2002) Int. J. Dev. Biol. 46: 777-783). Our interest at this moment is that the way of gastrulation movement of Xenopus is conserved in other amphibian species. If we find any substantial similarity between these species, we believe it helps us to understand the mechanisms of gastrulation latent in vertebrate species. So far we have obtained 20-30 thousands of brand-new genes expressing in several developing stages of Japanese newt, and are comparing their spatiotemporal expression pattern with that of Xenopus. Also we are working with about 15 species of Japanese amphibians. Using several staining strategies, we are trying to know how the gastrulation movements are progressed in those amphibian species.
We also have an interest in the neural crest formation both in development and evolution. In Xenopus neural crest formation, the function of growth factors and the transcriptional cascade are well studied. However intracellular circumstances necessary for neural crest formation, have not yet been understood. We proposed the maintenance of the future neural crest cell as proliferative state, is important for the neural crest formation (Nagatomo K. and Hashimoto C. (2007) Dev.Dyn. 236:1475-1483). Now we are working on some G protein coupled 7 trans-membrane type receptors, which are lately turned out to have important roles for the neural crest formation. We also have obtained the information of expression patterns of several genes of newt, which are known to be important for the neural crest formation in Xenopus, and found lots of differences from each other. Comparing those differences may lead us to understand the way neural crest is formed.