| Abstract: |
In the process of skin pattern formation, each cell must be able to recognize its position, which implies the existence of positional information within the embryo. Since skin patterns are not related to internal structures, the generation of this positional information must be autonomous, arising spontaneously without the need for predetermined initial conditions. As a theoretical framework for such autonomous spatial pattern formation, Turing’s principle was proposed in 1952. It describes how “waves” generated by the interactions of two types of molecules could create positional information. For decades, however, this remained largely hypothetical and was not widely accepted. Subsequent studies demonstrated that the stripe patterns of tropical fish behave in accordance with the theory of reaction–diffusion waves, providing the first empirical evidence for the existence of Turing waves. Experimental work using zebrafish later clarified the cellular mechanisms underlying wave formation. It is now recognized that Turing waves operate not only in animal skin but also more broadly in morphogenetic processes, and they are regarded as one of the fundamental principles of developmental biology. From a theoretical standpoint, nearly all spatial patterns observed in living organisms can be generated through Turing waves. Thus, the phenomenon of pattern formation has been conceptually resolved and is no longer considered a major enigma. This shift highlights the need to seek new directions for further challenge. One limitation of the Turing framework is that it assumes the prior existence of an unchanging “field” in which patterns emerge. In contrast, morphogenesis in living organisms involves the creation of that very field itself. In this sense, what is typically referred to as “pattern formation” may be seen merely as a subdivision of an already established field, without in itself generating form. Recent research has begun to address this issue using insect exoskeletons as a model system. The final part of this lecture will present some of the latest findings from this new line of investigation. |
