During development, the early differentiation of the geniculate and nodose ganglia is regulated by a series of transcription factors and signals from the pharyngeal pouch endoderm. The Six and Eya families of transcription factors are important for the development of multiple placodes, including the epibranchial placodes, from a single, common placode. In this pan-placodal area, Pax2 expression demarcates a region that forms the epibranchial and otic placodes. Signals from the pharyngeal pouch endoderm, like members of the bone morphogenic protein family (BMP), are required to induce epibranchial placode formation. Also, neurogenin 2 (Ngn2) and Phox2a signaling are important for neuronal differentiation within the placodes. Both are dependent on Eya1, but independent of one other. Phox2b is dependent on both Phox2a and Ngn2. Phox2 genes may be important for general neuronal differentiation as well as for differentiation of neuron subtypes. We propose that an unidentified factor(s) regulates the differentiation of gustatory phenotype and subtypes within these ganglia.
Krimm BMC Neuroscience 2007 8(Suppl 3):S4 doi:10.1186/1471-2202-8-S3-S4