Sensory Placode Formation in Vertebrates

Abstract

The sensory nervous system in the vertebrate head comprises a diverse set of organs: the eye, ear and olfactory epithelium and the sensory ganglia that transmit touch, pain, temperature and gustatory information to the brain. Sensory placodes are transient embryonic structures that make major contributions to these organs, and they in turn arise from a common pool of sensory progenitor cells. These progenitors are gradually induced at the border of the neural plate by a combination of FGF signaling and BMP and Wnt antagonism. Members of the Six and Eya family are important specifiers for sensory progenitors, but also play a role at later placode stages. As distinct placodes are induced by localized signals they become molecularly distinct and interactions with neural crest cells and other tissues ensure that the central and peripheral components of the sensory nervous system develop in register. Here I review the signaling and transcription factor networks that control sensory progenitor formation, and the subsequent events that govern the induction of individual placodes.