Evidence to support the distal vagal ganglion as the origin of C cells of the ultimobranchial gland in the chick.

Formation and development of the ultimobranchial anlage were studied in chicken embryos by immunohistochemistry with the antibodies to class III beta-tubulin, TuJ1, human leukemic cell-line (HNK-1), and protein gene product (PGP) 9.5, all of which recognized neurons. Medial to the fourth aortic arch, the ultimobranchial anlage was formed by the extension of the ventral portion of the fourth pharyngeal pouch at 4.5 days of incubation. At 5 days of incubation, TuJ1-immunoreactive cells with long cell processes began to enter the ultimobranchial anlage, which displayed a follicle structure. At 6 days of incubation, numerous neuronal cells that were continuous with the distal vagal ganglion (nodose ganglion) and expressed immunoreactivity for TuJ1, HNK-1, and PGP 9.5 were found to be in direct contact with the peripheral portion of ultimobranchial anlage. The TuJ1 antibody reacted only with the neuronal cells, whereas the HNK-1 and PGP 9.5 antibodies reacted with both endodermal epithelial cells and the neuronal cells in the ultimobranchial anlage. Subsequently, the ultimobranchial anlage rapidly increased in size; the follicle wall was thickened and a central cavity disappeared. The TuJ1-immunoreactive cells were distributed throughout the ultimobranchial parenchyma in 7-day-old embryos. The neuronal cell streams from the distal vagal ganglion to the ultimobranchial anlage were still prominent at 8 days of incubation. Almost all parenchymal cells of the ultimobranchial glands were intensely immunoreactive for TuJ1, HNK-1, and PGP 9.5 between 10 and 16 days of incubation. These results indicate that the neuronal cells from the distal vagal ganglion enter into the ultimobranchial anlage and give rise to C cells, i.e., C cells differentiate along the neuronal lineage. During embryonic development, C cells of the chick ultimobranchial glands transiently express a number of neuronal properties.