Cell biological mechanisms regulating chick neurogenesis.

Signalling pathways that regulate neural progenitor proliferation and neuronal differentiation have been identified. However, we know much less about how transduction of such signals is regulated within neuroepithelial cells to direct cell fate choice during mitosis and subsequent neuronal differentiation. Here we review recent advances in the experimentally amenable chick embryo, which reveal that this involves association of signalling pathway components with cell biological entities, including mitotic centrosomes and ciliary structures. This includes changing centrosomal localization of protein kinase A, which regulates Sonic hedgehog signalling and so neural progenitor status, and Mindbomb1, a mediator of Notch ligand activation, which promotes Notch signalling in neighbouring cells, and so is active in presumptive neurons. We further review cell biological events that underlie the later step of neuronal delamination, during which a newborn neuron detaches from its neighbouring cells and undergoes a process known as apical abscission. This involves inter-dependent actin and microtubule dynamics and includes dissociation of the centrosome from the ciliary membrane, which potentially alters the signalling repertoire of this now post-mitotic cell. Open questions and future directions are discussed along with technological advances which improve accuracy of gene manipulation, monitoring of protein dynamics and quantification of cell biological processes in living tissues.