A crucial process in embryonic development is the formation of localised signalling centres at boundaries between different tissue compartments. In vertebrates, this process can be studied in the hindbrain, which is segmented into compartments called rhombomeres. In their study of hindbrain boundaries in zebrafish (see p. 775), Amoyel and colleagues have now discovered that Wnt1 signalling maintains a sharp boundary between rhombomeres through the process of lateral inhibition. Unexpectedly,Wnt1 also promotes neurogenesis in rhombomeres, contrasting with previous findings in mice showing Wnt1 to be an inhibitor of neuronal differentiation in this region. Importantly, the molecular networks reported here –which were investigated by morpholino knockdowns of Wnt pathway components,and which involve both Notch and Wnt signalling – are very similar to those acting at the dorsal-ventral boundary of the fly wing, highlighting this as a fundamental process in boundary specification.

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