Gamma-aminobutyric acid is an inhibitory neurotransmitter, synthesized by two isoforms of glutamate decarboxylase (GAD), GAD65 and -67. Unexpectedly, inactivation of GAD67 induces cleft palate in mice. Reduction of spontaneous tongue movement resulting from decreased motor nerve activity has been related to the development of cleft palate in GAD67−/− fetuses. In the present study, development of cleft palate was examined histologically and manipulated with culture of the maxilla and partial resection of fetal tongue.
GAD67−/− mice and their littermates were used. Histological examination and immunohistochemistry were performed conventionally. Organ culture of the maxilla was carried out as reported previously. Fetuses were maintained alive under anesthesia and tips of their tongues were resected.
Elevation of palatal shelves, the second step of palate formation, was not observed in GAD67−/− mice. In wild-type mice, GAD67 and gamma-aminobutyric acid were not expressed in the palatal shelves, except in the medial edge epithelium. During 2 days of culture of maxillae dissected from E13.5–E14.0 GAD67−/− fetuses, elevation and fusion of the palatal shelves were induced. When E13.5–15.5 mutant fetuses underwent partial tongue resection, the palatal shelves became elevated within 30 min.
These results suggest that the potential for palate formation is maintained in the palatal shelves of GAD67−/− fetuses, but it is obstructed by other, probably neural, factors, resulting in cleft palate. Birth Defects Research (Part A) 2007. © 2007 Wiley-Liss, Inc.