Control of hindbrain motor neuron differentiation by the homeobox gene Phox2b

Motor neurons are a widely studied model of vertebrate neurogenesis. They c an be subdivided in somatic, branchial and visceral motor neurons. Recent s tudies on the dorsoventral patterning of the rhombencephalon have implicate d the homeobox genes Pax6 and Nkx2.2 in the early divergence of the transcr iptional programme of hindbrain somatic and visceral motor neuronal differe ntiation. We provide genetic evidence that the paired-like homeodomain prot ein Phox2b is required for the formation of all branchial and visceral, but not somatic, motor neurons in the hindbrain. In mice lacking Phox2b, both the generic and subtype-specific programs of motoneuronal differentiation a re disrupted at an early stage. Most motor neuron precursors die inside the neuroepithelium while those that emigrate to the mantle layer fail to swit ch on early postmitotic markers and to downregulate neuroepithelial markers , Thus, the loss of function of Phox2b in hindbrain motor neurons exemplifi es a novel control point in the generation of CNS neurons.