Multivesicular bodies

theoreticians in developmental biology, as mainstream opinion held that one had to clone the genes involved and isolate the corresponding molecules — and that development would then be understood. The interest in theories was correspondingly low. At this time, the fascinating and beautiful patterns on shells were for me an inspiring looking glass to study the richness of patterns that can emerge if several patterning systems are superimposed. Because the shell patterns are time records, they preserve the complete history of their formation — an exceptional advantage for decoding the underlying dynamics. It has turned out that, depending on half life, strength of interactions and other parameters, the same molecular interaction can lead to very different patterns. Without an explicit quantitative model, one cannot predict directly the emerging pattern, even if all the individual components involved are known. This is a system property, requiring mathematics to be understood. The shell work had a high pay off for me. The lessons I learned from them were later a key to understand other highly dynamic patterning systems, for example how, in an Escherichia coli bacterium the cell centre is identified as the place to initiate cell division, or how the dynamic signalling can be achieved that leads to the ever changing pseudopod formation at the cortex of a motile eukaryotic cell. Do you have a favourite paper? The discovery by Hobmayer et al. that the canonical Wnt-pathway is crucial for the formation of the hydra organizer, reported in their 2000 paper 'WNT signalling molecules act in axis formation in the diploblastic metazoan' (Nature 407, 186-189), was a key for me in several respects. Together with other data, this work allowed the hypothesis that the body of a hydra-like, radially symmetrical ancestor evolved into the brain and heart of higher organisms. In this view, midline formation — a precondition for a central nervous system — and trunk formation were later evolutionary inventions. In this light, therefore, the brains of vertebrates and insects are under the control of the same genes, although the common ancestor had presumably no brain: both are derived from the body pattern of a common hydra-like ancestor. Moreover, we have known for more than 80 years that the Spemann organizer is decisive for axis formation in vertebrates. But we have two main body axes, not just an anteroposterior axis but a dorsoventral one as well. Starting from the data in …