Neurogenin 2 and Neuronal Differentiation 1 control proper development of the chick trigeminal ganglion and its nerve branches

Abstract

The trigeminal ganglion contains the cell bodies of sensory neurons comprising cranial nerve V, which relays information related to pain, touch, and temperature from the face and head to the brain. Like other cranial ganglia, the trigeminal ganglion is composed of neuronal derivatives of two critical em-bryonic cell types, neural crest and placode cells. Neurogenesis within the cranial ganglia is promoted by Neurogenin 2 (hereafter referred to as Neurog2), which is expressed in trigeminal placode cells and their neuronal derivatives and transcriptionally activates neuronal differentiation genes like Neuronal Differentiation 1 (NeuroD1). Little is known, however, about the role of Neurog2 and NeuroD1 dur-ing chick trigeminal gangliogenesis. To address this, we depleted Neurog2 and NeuroD1 from trigemi-nal placode cells with morpholinos and demonstrated that Neurog2 and NeuroD1 influence trigeminal ganglion development. While knockdown of both Neurog2 and NeuroD1 affected innervation of the eye, Neurog2 and NeuroD1 had opposite effects on ophthalmic nerve branch organization. Taken to-gether, our results highlight, for the first time, functional roles for Neurog2 and NeuroD1 during chick trigeminal gangliogenesis. These studies shed new light on the molecular mechanisms underlying tri-geminal ganglion formation and may also provide insight into general cranial gangliogenesis and dis-eases of the peripheral nervous system.