Sprouty genes are essential for the normal development of epibranchial ganglia in the mouse embryo.
Bottom Line: Fibroblast growth factor (FGF) signalling has important roles in the development of the embryonic pharyngeal (branchial) arches, but its effects on innervation of the arches and associated structures have not been studied extensively.However, epithelial-specific gene deletion only results in defects in the facial nerve and not the glossopharyngeal and vagus nerves, suggesting that the facial nerve is most sensitive to perturbations in RTK signalling.Reducing the Fgf8 gene dosage only partially rescued defects in the glossopharyngeal nerve and was not sufficient to rescue facial nerve defects, suggesting that FGF8 is functionally redundant with other RTK ligands during facial nerve development.
Affiliation: Department of Craniofacial Development, King's College London, Floor 27, Guy's Tower, London, SE1 9RT, UK.Show MeSH
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Mentions: One of the first markers for epibranchial placode specification is the proneural gene, Ngn2 (Fode et al., 1998; Sommer et al., 1996). To assess whether the specification of individual epibranchial placodes was compromised in the Sprouty mutants, whole mount in situ hybridisation using a Ngn2 riboprobe was performed at E9.5 (Fig. 3A). Ngn2 expression was expanded at the anterodorsal margin of the second arch, indicating an enlargement of the geniculate placode in the Spry1−/−;Spry2−/− embryos (Fig. 3B; n = 4). This is in line with the observation of a larger facial ganglion in Spry1−/−;Spry2−/− embryos at E10.5 (Fig. 2). By contrast, the petrosal and nodose placodes appeared smaller or missing in the Spry1−/−;Spry2−/− mutants at E9.5 (Fig. 3B; n = 4). These observations suggest that increased RTK signalling has opposite effects on the geniculate versus petrosal and nodose placodes at the time of their formation.
Affiliation: Department of Craniofacial Development, King's College London, Floor 27, Guy's Tower, London, SE1 9RT, UK.