Hes1 is required for the development of pharyngeal organs and survival of neural crest-derived mesenchymal cells in pharyngeal arches.

Hes genes are required to maintain diverse progenitor cell populations during embryonic development. Loss of Hes1 results in a spectrum of malformations of pharyngeal endoderm-derived organs, including the ultimobranchial body (progenitor of C cells), parathyroid, thymus and thyroid glands, together with highly penetrant C-cell aplasia (81%) and parathyroid aplasia (28%). The hypoplastic parathyroid and thymus are mostly located around the pharyngeal cavity, even at embryonic day (E) 15.5 to E18.5, indicating the failure of migration of the organs. To clarify the relationship between these phenotypes and neural crest cells, we examine fate mapping of neural crest cells colonized in pharyngeal arches in Hes1 null mutants by using the Wnt1-Cre/R26R reporter system. In null mutants, the number of neural crest cells labeled by X-gal staining is markedly decreased in the pharyngeal mesenchyme at E12.5 when the primordia of the thymus, parathyroid and ultimobranchial body migrate toward their destinations. Furthermore, phospho-Histone-H3-positive proliferating cells are reduced in number in the pharyngeal mesenchyme at this stage. Our data indicate that the development of pharyngeal organs and survival of neural-crest-derived mesenchyme in pharyngeal arches are critically dependent on Hes1. We propose that the defective survival of neural-crest-derived mesenchymal cells in pharyngeal arches directly or indirectly leads to deficiencies of pharyngeal organs.

Development of thyroid gland and ultimobranchial body cyst is independent of p63.

The ultimobranchial body (UBB) and thyroid primordium are the origins of the thyroid gland that fuse around embryonic day 14.5 of mouse gestation, ultimately giving rise to calcitonin-producing C cells and thyroglobulin-producing follicular cells, respectively. A homeodomain transcription factor NKX2-1 is expressed both in the UBB and the thyroid primordium, and is critical for development of the thyroid gland. In this study, the role of p63 in development of UBB and the thyroid gland was analyzed by histological, immunohistochemical, and electron microscopic analyses using mice with various combinations of Nkx2-1 and p63 wild-type, heterozygous, and null alleles. In the absence of p63, a normal thyroid gland develops, as revealed by expression of thyroglobulin and calcitonin, thus showing that p63 is not required for thyroid development. However, in mice carrying the Nkx2-1-null allele, the UBB remains as a cystic vesicular structure and/or in nested patterns consisting of p63-positive cells surrounding the vesicle and undifferentiated immature cells with occasional cilia lying inside. The cystic UBB was present even in the Nkx2-1;p63 double-null mice. The structure and p63 expression pattern of the UBB cyst strikingly resemble the solid cell nest. These results show that in the absence of NKX2-1, UBB becomes cystic independent of p63, which is likely the origin of SCN.

Origin of the ultimobranchial body cyst: T/ebp/Nkx2.1 expression is required for development and fusion of the ultimobranchial body to the thyroid.

The ultimobranchial body (UBB) is an outpocketing of the fourth pharyngeal pouch that fuses with the thyroid diverticulum, giving rise to calcitonin-producing C-cells. In this study, we demonstrate that the UBB is composed of two types of cells: one expressing T/ebp/Nkx2.1 and the other expressing p63. The former cell type, accounting for a majority of the UBB, requires T/ebp/Nkx2.1 for their survival. In contrast, the p63-positive cells, even in the absence of T/ebp/Nkx2.1 expression, can proliferate and give rise to a vesicular structure that is lined by a monolayer of p63-negative cells, surrounded by a cluster and/or single layer of p63-positive cells, displaying the basal/stem cell phenotype. T/ebp/Nkx2.1 haploinsufficiency causes abnormal fusion of the UBB with the thyroid diverticulum, which stays as a cluster of C-cells around the vesicular structure, similar to the one observed in mice null for T/ebp/Nkx2.1 expression. These results demonstrate that T/ebp/Nkx2.1 plays a role in the survival of UBB cells, their dissemination into the thyroid diverticulum, and the formation of UBB-derived vesicular structure.

Salivary heterotopia, cysts, and the parathyroid gland: branchial pouch derivatives and remnants.

Five cases of periparathyroid salivary heterotopia associated with cysts were studied. The specimens were obtained from three men and two women age 36 to 62 years who underwent surgery for primary hyperparathyroidism (four patients) and thyroid nodule (one patient). The heterotopia-cyst combination occurred with normal and abnormal parathyroid glands (four inferior and one of unknown location). Review of histologic slides of all parathyroid glands excised from 258 patients during a 1-year period at the Mayo Clinic revealed two similar salivary gland-cyst units. Seven more cases featured one or more periparathyroid cysts, five with other nonsalivary-type epithelial accompaniments. One of the latter additionally had a focus of parathyroid cells in the cyst wall, and associated thyroid parenchyma with C cells, and cartilage.

Localization of immunoreactive keratins in cyst epithelium of chick ultimobranchial glands.

The cyst structures of chick ultimobranchial glands were studied by electron microscopy and immunocytochemistry to characterize the type of intermediate-sized filaments present in the cells lining cyst lumina. Electron microscopy showed that the majority of the lumen-bordering cells contained extensive meshworks of intermediate-sized (7-11 nm) filaments, many of which were arranged in bundles. Apical regions of C cells directly bordering on cyst lumina were also filled with thinner (5-6 nm) filaments. Immunoperoxidase staining showed that the majority of cyst epithelial cells were stained intensely with anti-keratin antiserum, but not with anti-neurofilament antiserum, which is a specific marker for neuronal differentiation. The cyst epithelium also showed moderate-to-weak immunoreactivity for actin. Subsequently, the differentiation and maturation of cyst structures related to intermediate filament expression were studied. In 18-day-old chick embryos, keratin immunoreactivity began to appear in the cell clusters destined to form cysts and in the primordial cysts with small cavities. At this time, fine networks of intermediate filaments were already detected in the cells lining the cystic cavities. At 1 day after hatching, the cysts became a consistent feature of ultimobranchial glands. Intermediate filaments associated in bundles were observed, and the intensity of immunostaining for keratins increased. Thereafter, with progressive enlargement of cysts, numbers of intermediate filaments and intensity of keratin immunoreactivity gradually increased with age. Thus, the data indicate that in cyst epithelium keratin filaments are highly organized and may confer the structural strength necessary for cells lining cyst lumina.

A study on the relationship between solid cell nests and mucoepidermoid carcinoma of the thyroid.

Mucoepidermoid carcinoma of the thyroid (MECT) has been recently recognized as a pathological entity. The origin of MECT is unknown but the morphology of this tumour closely resembles features seen in the ultimobranchial body (UB) vestiges. Recent studies in man have shown strong evidence that the so-called solid cell nests (SCN) of the thyroid may correspond to the human UB vestiges. To investigate whether these vestiges are the site of origin of this tumour a comparative study on SCN and MECT was undertaken. One hundred autopsied thyroids cut at 2-3 mm intervals were studied for the presence of SCN. Histochemical (H & E, Alcian blue-PAS, Mayer mucicarmine) and immunohistochemical studies (calcitonin, epidermal keratin) were performed in SCN and four cases of MECT. Sixty percent of thyroids were found to have SCN. They were mainly composed of epidermoid-like cells arranged in solid structures or lining cystic cavities, tubular and follicular structures. Solid clusters usually showed lumina containing PAS-positive and mucin-positive cell debris. Mucin stains also revealed mucinous cells placed around lumina filled by mucosubstances. Characteristic PAS-positive rounded bodies were found filling lumina as well as within some apical epidermoid-like cells, mucinous cells and cell debris. An obvious transition between these cells, cell debris and mucosubstances filling the lumina was noticed; suggesting degenerative changes undergone by the epidermoid-like cell. MECT basically presented all histological and histochemical features shown by SCN, furthermore, calcitonin containing cells were observed in 54% of SCN, while a metastatic MECT also showed scattered C cells within solid islands. The presence of epidermal keratin in all SCN and MECT, together with the previous findings, are strong evidence that MECT could originate in the SCN or human UB vestiges.

Ontogeny of chicken ultimobranchial glands studied by an immunoperoxidase method using calcitonin, somatostatin and 19S-thyroglobulin antisera.

The ontogeny of the ultimobranchial glands in chickens from 9-day-old embryos to adults was investigated by the immunoperoxidase method using anti-calcitonin, anti-somatostatin and anti-19S-thyroglobulin antisera. During embryonic development, the chick ultimobranchial glands consisted of solid cell clusters. Calcitonin immunoreactivity began to appear at 16 days of incubation and rapidly increased at late periods of incubation. At the time of hatching, almost all of the epithelial cells in the ultimobranchial glands exhibited the immunoreaction for calcitonin. Cyst structures showing various sizes, shapes and luminal contents were consistent features of the ultimobranchial glands after hatching. As age proceeded, the cysts and loose connective tissues gradually increased in the glands. In adult chickens, the calcitonin cells came to be interspersed among them and the number of the cells per unit area was very small, compared with that in young animals. No immunoreaction for somatostatin was found in the ultimobranchial glands of chickens of all ages examined. In the glands there were no cells immunoreactive to the 19S-thyroglobulin antiserum. Further, neither cyst epithelium nor luminal contents were stained with the antiserum.

[Value of immunohistochemistry in the study of medullary cancer of the thyroid. Implications of the results for the concept of the APUD system and of apudomas]. / Intérêt de l'immunohistochimie dans l'étude du cancer médullaire de la thyroïde. Implication des résultats pour le concept de système "A.P.U.D." et d'"apudome".

Immunohistochemical studies in medullary thyroid carcinoma demonstrate the presence of C cells secreting calcitonin but also of other cells secreting other peptides or proteins. These different cells exist in the tumor as well as in metastases. These results and other reported in the literature suggest a common ultimobranchial and endodermal origin for these cells.

Position of ultimobranchial body cysts in the human fetal thyroid gland.

In a series of 21 human fetal thyroid glands examined histologically in serial sections, seven ultimobranchial body cysts were found. The position of these cysts correlated well with the distribution of calcitonin-containing cells found by previous investigators in the adult thyroid gland. Ultimobranchial body cysts found external to the thyroid lobes may offer a developmental explanation for the paucity of calcitonin found in some adult thyroid glands. The close developmental relationship between the parathyroid gland and the ultimobranchial body could explain the presence of calcitonin found in these glands in some adults.