The intricate pathways and processes that are involved in building a fully functional nervous system are quite remarkable — no less so than the finished product itself. Rather than deterring researchers, the complexity of neural development has inspired a huge research effort, and this month we are delighted to present articles that describe progress in two important areas of investigation.
Bone morphogenetic protein (BMP) signalling is the focus of Liu and Niswander's review, one of our series of articles on signalling in neural development. Starting with the early decision to form neural ectoderm, BMP signalling is essential for many aspects of neural development, from patterning and proliferation of the spinal cord to embryonic and postnatal brain development. In addition to learning more about the interactions of BMPs with other developmental signals, the authors note that one of the challenges ahead is to discover the functions of BMPs at later stages of development — for example, in synapse formation.
Innocenti and Price focus on the development of neural circuits, describing the phenomenon of 'developmental exuberance' — the overproduction of axons, axonal branches and synapses, followed by selection. The authors discuss the relative roles of pre-specified connectivity and exuberance in the formation of neural circuits, proposing that exuberance and selection might have favoured flexible development and evolution of the brain. Technical obstacles will need to be overcome if we are to extend our knowledge of exuberance to the human brain and, importantly, to disorders of brain function.
The fascinating insights that we have gained during the past few years have highlighted the many and varied mechanisms that contribute to nervous system development. The hope is that progress on all fronts will continue apace.
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In This Issue. Nat Rev Neurosci 6, 911 (2005). https://doi.org/10.1038/nrn1823