Expression of Retinaldehyde Dehydrogenases in the Pituitary Glands of Fetus and Adult Mice

Retinoic acid (RA) plays a critical role in cell growth and tissue development. RA is synthesized from retinoids through oxidation processes by the retinaldehyde dehydrogenase (Raldh) family. However, the expression of Raldhs during pituitary development and the identification of Raldh-expressing cells in the adult pituitary have not been fully elucidated. Here, we performed in situ hybridization to localize the three Raldh isoforms (Raldh1-3) in fetal and adult mouse pituitary glands. The results showed that Raldh2 expression was observed in Rathke's pouch from embryonic day 13.5 (E13.5), and this expression was sustained in the anterior lobe of the pituitary primordium from E15.5 to E17.5. In contrast, Raldh1 and Raldh3 were rarely detectable. Real-time PCR analysis revealed that Raldh2 was the predominant isoform expressed in the adult pituitary, although Raldh1 was also expressed to a lesser extent. In the adult pituitary, Raldh1-expressing cells were primarily observed in the posterior lobe. Raldh2-expressing cells were found in the marginal cell layer and parenchyma of the anterior lobe and were immunopositive for aldolase C (folliculostellate cells), but not for anterior pituitary hormones. These results suggest that RA is an important regulatory factor in the functions of the pituitary throughout its development in mice.