Spemann's influence on Japanese developmental biology

The discovery of the organizer by H. Spemann and Hilde Mangold, prompted a number of studies of embryonic induction in Japan. C.O. Whitman, N. Yatsu, T. Sato, H. Oka, T. Yamada, and Y.K. Okada were the pioneers in the field of embryonic induction. T. Yamada postulated the double potential theory for embryonic induction. O. Nakamura has modified the fate map of Vogt using newt and Xenopusblastulae. T.S. Okada and G. Eguchi proposed the new concept of "transdifferentiation" based on in vitro experiments in the retina and lens. T.S. Okada is not only an excellent scientist, but he has also nurtured many active developmental biologists. M. Takeichi, from his school, discovered the cell adhesion molecle, cadherin. Nakamura and colleagues tried to determine the origin and formation of the organizer. They performed recombination experiments using the ectoderm, endoderm and mesoderm, and concluded that the phenomenon in which various mesoderm tissues are formed by the recombination of the presumptive ectoderm with endoderm was "regulation of the vegetal-animal gradient". Some groups have also tried to purify specific inducing factors. T. Yamada and colleagues isolated two different types of ribonucleoproteins. I. Kawakami and colleagues showed that the ribosome fraction has neural inducing capacity, and that the extracellular matrix contains mesodermal inducing factors. Finally Asashima and colleagues isolated and identified activin A as a MIF factor. This finding had a great influence not only in the field of developmental biology, but also in molecular biology. Using activin, Asashima's group has successfully generated various organs, tissues, trunk-tail and head structures in vitro using animal caps (undifferentiated cells). Some other important molecules such as BMP, chordin and bFGF are also being studied by young Japanese scientists.