Fig. 8. Schemata depicting the role of foxi1 in visceral sensory neuron development. (A) Among foxi1-expressing cells (red), neuronal precursors delaminate and express ngn (yellow) and phox2a (green) to adopt epibranchial sensory identity. Foxi1 expression in the placodal progenitor cells coordinate the expression of ngn and phox2a, which regulate neuronal fate and subtype specification, respectively. (B) Dorsal views of the foxi1-expressing domain (red), ngn-expressing domain (yellow), and phox2a-expressing domain (green). the foxi1-expressing domain in the tail bud stage embryos (top) defines the epibranchial (and otic) placodal progenitor cells, from which ngn⁺ and phox2a⁺ neuronal precursors are specified in a rostral to caudal sequence (middle, 24 hpf; bottom, 32 hpf). In the no soul mutant, epibranchial placodal progenitors cells are born but their neuronal specification fails to occur, resulting in the subsequent loss of placodal progenitor cells by apoptosis and absence of visceral sensory neurons at later stages. The nodose ganglion may be formed by foxi1-independent mechanisms or by compensation from other cell lineages. (C) Hierarchical regulation in visceral sensory neuronal determination.