A comparative ultrastructural study on ultimobranchial glands of some Israeli anurans (Bufo viridis, Rana ridibunda and Hyla arborea)

Morphological and molecular evolution of the ultimobranchial gland of nonmammalian vertebrates, with special reference to the chicken C cells

This review summarizes the current understanding of the nonmammalian ultimobranchial gland from morphological and molecular perspectives. Ultimobranchial anlage of all animal species develops from the last pharyngeal pouch. The genes involved in the development of pharyngeal pouches are well conserved across vertebrates. The ultimobranchial anlage of nonmammalian vertebrates and monotremes does not merge with the thyroid, remaining as an independent organ throughout adulthood. Although C cells of all animal species secrete calcitonin, the shape, cellular components and location of the ultimobranchial gland vary from species to species. Avian ultimobranchial gland is unique in several phylogenic aspects; the organ is located between the vagus and recurrent laryngeal nerves at the upper thorax and is densely innervated by branches emanating from them. In chick embryos, TuJ1-, HNK-1-, and PGP 9.5-immunoreactive cells that originate from the distal vagal (nodose) ganglion, colonize the ultimobranchial anlage and differentiate into C cells; neuronal cells give rise to C cells. Like C cells of mammals, the cells of fishes, amphibians, reptiles, and also a subset of C cells of birds, appear to be derived from the endodermal epithelium forming ultimobranchial anlage. Thus, the avian ultimobranchial C cells may have dual origins, neural progenitors and endodermal epithelium. Developmental Dynamics 246:719-739, 2017. © 2017 Wiley Periodicals, Inc.

Ultrastructural localization of immunoreactive calcitonin in the two cell types of the ultimobranchial gland of the common toad (Bufo bufo L.)

The ultimobranchial (UB) glands of the common toad Bufo bufo consist of several cellular masses containing two quite different cell types which line a central lumen filled with amorphous material. The morphologically defined Type I cell is akin to a typical calcitonin secretory cell as observed for all vertebrates, with small dense-core secretory granules. On the contrary the Type II cell displays large apical dense bodies which may be related to the secretion and/or absorption of the amorphous material. Cells morphologically related to Type II cells have been described in the UB glands of Sauropsidea and in the UB follicles of mammalian thyroid gland. An immunocytochemical stain using an antiserum raised against synthetic salmon calcitonin demonstrated the specific localization of an immunoreactive product in both Type I and Type II cell granules, suggesting that both cell types could be involved in calcitonin metabolism. Moreover, the presence of immunoreactive calcitonin in the Type II cells of the Bufo UB gland raises the question of the function of the morphologically equivalent cells of other species.

Ultimobranchial gland of the domestic fowl. Two types of secretory cells involved in calcitonin metabolism

The ultimobranchial gland (UBG) of birds is particularly rich in calcitonin, the hypocalcaemic hypophosphataemic hormone, that is secreted by the C-cells of the mammalian thyroid. The principal cells of the UBG have a striking resemblance with the mammalian C-cells, i.e., they possess small intracytoplasmic dense-core secretory granules, 150-300 nm in diameter. The gland also contains a second, morphologically distinct, endocrine cell type with larger granules, 500-800 nm in diameter. A sensitive immunocytochemical reaction was developed with the use of antibodies against salmon calcitonin. By means of this technique the presence of calcitonin-immunoreactive molecules was demonstrated in both secretory cell types of the UB gland of the chicken. This gland can thus be considered as a homogeneous calcitonin-producing tissue. Whether the secretory products are identical is discussed and differences in the secretory pathways are suggested.