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It has been reported that a subset of type III taste cells express glutamate decarboxylase (GAD)67, which is a molecule that synthesizes gamma-aminobutyric acid (GABA), and that Mash1 could be a potential regulator of the development of GABAnergic neurons via Dlx transcription factors in the central nervous system. In this study, we investigated the expression of GAD67 and Dlx in the embryonic taste buds of the soft palate and circumvallate papilla using Mash1 knockout (KO)/GAD67-GFP knock-in mice. In the wild-type animal, a subset of type III taste cells contained GAD67 in the taste buds of the soft palate and the developing circumvallate papilla, whereas GAD67-expressing taste bud cells were missing from Mash1 KO mice. A subset of type III cells expressed mRNA for Dlx5 in the wild-type animals, whereas Dlx5-expressing cells were not evident in the apical part of the circumvallate papilla and taste buds in the soft palate of Mash1 KO mice. Our results suggest that Mash1 is required for the expression of GAD67 and Dlx5 in taste bud cells., (© The Author 2014. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Much attention has been focused on the mechanisms responsible for the elevation and fusion of the palatal processes during formation of the secondary palate. In a former publication this closure, defined as fusion of the palatal shelves along their length, was described as occurring at a period in osseous palatal development characterized by incipient ossification of the maxillae and palatine bones, and at a stage in early mandibular development when the mandibular condyle has not developed. The purpose of the present study was to examine the osseous maturation of the cranial base at the time of palatal closure. The investigation was based on 62 human embryos and fetuses, CRL 22-57 mm, and general skeletal hand and foot maturation CNO = 0-0 to CNO = 8-1 (CNO, Composite Number of Ossified bones in hand and foot). From the fetuses, cranial tissue was dissected out and skeletal maturity was determined radiographically according to formerly described skeletal maturity stages in the cranial base. The study revealed that the soft tissue palatal shelves always elevate and fuse along their length at a specific, well-defined stage of maturity in the cranial base. The cranial base development in this stage is characterized by unossified cartilage. This information is essential for understanding abnormal skeletal development of the oral and nasal cavities.