Differential retinoic acid sensitivity of oral and pharyngeal teeth in medaka (Oryzias latipes) supports the importance of pouch–cleft contacts in pharyngeal tooth initiation

Previous studies have claimed that pharyngeal teeth in medaka (Oryzias latipes) are induced independent of retinoic acid (RA) signaling, unlike in zebrafish (Danio rerio). In zebrafish, pharyngeal tooth formation depends on a proper physical contact between the embryonic endodermal pouch anterior to the site of tooth formation, and the adjacent ectodermal cleft, an RA-dependent process. Here, we test the hypothesis that a proper pouch-cleft contact is required for pharyngeal tooth formation in embryonic medaka, as it is in zebrafish. We used 4-diethylaminobenzaldehyde (DEAB) to pharmacologically inhibit RA production, and thus pouch-cleft contacts, in experiments strictly controlled in time, and analyzed these using high-resolution imaging.