Figure 7
From: Tbx1 and Brn4regulate retinoic acid metabolic genes during cochlear morphogenesis
Model of Tbx1 and Brn4 function in the POM. Sonic hedgehog (Shh) secreted from the notochord (circle) and floor plate regulates both Tbx1 and Brn4 in the POM (blue). This signal is likely mediated by Gli genes expressed in the POM. Tbx1 and Brn4 activate members of the Cyp26 family also expressed in the POM. These genes catabolize active retinoic acid (RA) secreted from the otic vesicle (green), thereby regulating RA activity in the POM. Brn4 regulates expression of Cyp26c1, while Tbx1 regulates both Cyp26a1 and Cyp26c1. Strict control of RA dosage in the POM is likely crucial for proper cochlear coiling. CD, cochlear duct; ED, endolymphatic duct; POM, periotic mesenchyme.