Two Rar genes show prominent expression in the developing pituitary gland: Rara (mainly the Rara1 isoform), expressed throughout the anterior pituitary anlage, and Rarb2, preferentially expressed in the periphery of the gland [Mollard et al., 2000]. Rxrg is also specifically expressed in the developing pituitary gland [Dolle et al., 1994], which furthermore expresses RA-synthesizing enzymes [Fujiwara et al., 2007]; the involvement of retinoid signaling in pituitary development has not been elucidated, however. Apart from Rara, no Rar transcripts were detected in the developing thyroid gland [Dolle et al., 1990]. Rarb and Rarg show differential distributions within the developing salivary glands, in mesenchymal and epithelial cells, respectively [Dolle et al., 1990]. Other glandular systems with Rarg expression include the ocular Harderian glands, which are absent in the corresponding null mutants [Lohnes et al., 1993].
