As far as development is concerned, the nervous system is probably the unrivalled champion of all systems in terms of complexity. Many questions are still perplexing the minds of developmental neuroscientists. For example, how is the neural tube patterned along the anterior–posterior and dorsoventral axes? How is it divided into specific territories that will define the final organization of the mature central nervous system? How do neural progenitors acquire specific cell fates and choose the correct migratory path? And how are axons guided along the long, treacherous journey to reach their correct targets and make functional connections? During the past few years, tremendous progress has been made in understanding the molecular mechanisms that are involved in all aspects of neural development — from embryonic patterning to neuronal connectivity. In this issue, Ciani and Salinas review the WNT signalling pathways and their myriad of functions in tissue patterning, cell fate determination, proliferation, migration, axon guidance and synapse formation (page 351). This review marks the beginning of a series of articles on signalling pathways in neural development, which will be published over the coming months.
The importance of WNTs in neural development is also the topic of a Research Highlight this month. “Maternal instinct” (page 347) describes a new study that identifies maternally-derived WNT11 as the initial signal that activates the canonical WNT signalling pathway in fertilized eggs. Activation of this pathway is crucial for dorsoventral axis formation, which was previously thought to be WNT-independent. The study also provides intriguing insights into the molecular mechanisms whereby WNTs act in conjunction with tissue-specific extracellular cofactors to activate different WNT pathways in various tissues.
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In this issue. Nat Rev Neurosci 6, 343 (2005). https://doi.org/10.1038/nrn1682