Palate development after fetal tongue removal in cortisone-treated mice

Morphological studies of cortisone-induced cleft palate have shown retardation in the rotation of palatine shelves from a sagittal to a transverse plane. Cortisone also reduces fetal muscular movements, which may explain why displacement of the tongue from between the palatine shelves is delayed. Previous work with extrauterine development of control fetuses demonstrated that fetal membranes and tongue were major obstacles to shelf rotation. Thus, removal of these obstacles might permit rotation and fusion of palatine shelves in cortisone-treated fetuses. In the present experiment, fetuses from cortisone-treated strain CD-1 mice were released from uterus and membranes and allowed to develop for eight hours in a fluid medium with the umbilical cord left intact. Compared to 4% fusion in utero, there was palatal fusion in 20% of fetuses released from membranes. When the fetal tongue was removed during extrauterine development, the frequency of fusions increased to 61%. Fusion appeared normal by the criteria applicable through light microscopy. Thus, cortisone induces cleft palate primarily through interference with shelf rotation. The palatine shelves of treated fetuses retain their ability to fuse when they can come in contact during the normal time for palate closure.