RA plays important roles for the development of nasal structures [Dupe et al., 2003; Halilagic et al., 2007]. Rarb exhibits region-specific expression in differentiating nasal structures, being present both in the mesenchyme and in specific areas of the olfactory epithelium [Dolle et al., 1990] (see Figure 4D). Knockout mouse models have shown that RARα and RARγ are important for the development of nasal structures [Lohnes et al., 1994]. Whether there is a function of RARβ in later development of the nasal cavities and/or differentiation of olfactory neurons is unclear [Ghyselinck et al., 1998; Luo et al., 1995]. It would be of interest to investigate whether Rarb-null mutant mice have an impaired olfaction.
