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.

Fine structure of the parathyroid and ultimobranchial glands of the snake, Elaphe quadrivirgata.

The ultrastructure of the parathyroid gland and ultimobranchial gland of the snake, Elaphe quadrivirgata, was studied. The parenchyma of the parathyroid gland was consisted of chief cells arranged in cords. Oxyphil cells and water-clear cells were not recognized. The chief cells contained irregular shaped nucleus, moderately-developed mitochondria, granular endoplasmic reticulum and Golgi complexes. A few secretory granules of 100-300 nm in diameter distributed in the cytoplasm. Small aggregations of glycogen particles and lipid droplets were dispersed widely in the cytoplasm. The ultimobranchial glands consisted of follicles and interfollicular aggregates of C-cells. Follicles were invaginated and composed of C-cells, goblet cells and ciliated cells. C-cells were located in the basal position of the follicle and possessed variety of secretory granules of 100-300 nm in diameter in the basal region of the cell. C-cells presented various secretory cycles. Goblet cells projected microvilli into follicular lumen. At the apical region the goblet cells had large granules of 300-1,200 nm in diameter. Ciliated cells projected cilia intermixed with micovilli from the apical surface of the cell into the follicular lumen.

Fine structure of the ultimobranchial body of the pheasant (Phasianus colchicus L.).

The pheasant's ultimobranchial body is characterized by the presence, in the connective tissue stroma, of epithelial cells between which two types of granulated cells comprising the main part of the glandular portion of the body are formed. Type I is characterized chiefly by the presence of nonrounded electron-dense secretory granules measuring 65-240 nm in the cytoplasm and by a very well-developed Golgi apparatus. The cytoplasm of type II cells also contains dark secretory granules, but somewhat smaller (50-150 nm). This type is very frequently in close contact with specific and often branching tubular structures from whose cells microvilli project into the lumen. The dark cytoplasm of the cells lining these structures contains a relatively large number of mitochondria and dense bodies, but no secretory granules.

The fine structure of the vesicular component of the ultimobranchial gland of the domestic fowl.

The ultrastructure of the polymorphic vesicular component of the ultimobranchial gland of the domestic fowl (Gallus gallus domesticus) has been described in detail, together with the structure of the cell strands interconnecting the vesicles and the parathyroid nodules lying within the ultimobranchial stroma. The vesicles frequently appear to arise from the nodules by way of the cell strands. The strands show a structure of their component cells intermediate between that of the parathyroid and the vesicular cells, although the position at which the strand changes from an essentially parathyroid structure to an essentially vesicular structure is very variable. The degree and kind of secretory activity within different cell types has been described. A review of the structure of ultimobranchial glands throughout the vertebrates shows that similar tissue with a similar secretory potential has been observed in all vertebrate classes, suggesting a functional significance for this part of the gland.

Ultrastructure of the ultimobranchial follicles of the laying chicken.

The ultimobranchial gland of the laying chicken consists of groups of C cells interspersed among a collection of intercommunicating follicles and ducts of variable size and shape. The epithelium lining this system ranges from squamous to columnar and includes stratified squamous and pseudostratified columnar elements. Four cell types are distinguished in this epithelium: F, mucous, C, and basal cells. F cells show microvilli and microfilaments. Pinocytotic activity and images of fusion of coated vesicles with the plasma membrane are evident. The rough-surfaced endoplasmic reticulum (RER) and the Golgi complex are moderately developed. Dense bodies are encountered apically in some cells. Mucous cells possess microvilli and secretory material in the typical form of partially fused droplets. C cells contain secretory granules and are invariably separated from the follicular lumen by other cell types. The smaller, pyramidal basal cells contain filaments, RER, small Golgi complexes, free ribosomes and hemidesmosomes. The lumina contain flocculent or granular material, cellular debris and desquamated cells. Morphological evidence demonstrates that features of the pharyngeal epithelium are retained and that the majority of the cell types, with the exception of C cells, are presumably nonendocrine.

The carotid body of the pheasant (Phasianus colchicus L.). An electron microscopy study.

In the pheasant, the carotid body lies laterally to the common carotid artery, is partly surrounded by parathyroid tissue and is immediately adjacent to the ultimobranchial body. In some cases these tissues intermingle. The cellular component of the carotid body consists primarily of granular endocrine cells, which are arranged in islands and lie in immediate proximity to wide capillaries and nerve fibres. A quantitative evaluation of granule size frequencies in these main cells, which we divided into three types, showed, inter alia, that the types represented three stages of cell differentiation, type III being the most mature cells. Only this last, i.e. mature, type can be used for differentiation from the granular cells of the ultimobranchial body of the same species, from which they differ. In addition, the main carotid body cells are typically surrounded by sustentacular cells. Numerous contacts with the terminal parts of axons were found on the main cells.

An ultrastructural study of the cysts in chicken ultimobranchial glands, with special reference to C-cells.

The ultimobranchial glands of the chicken were examined by electron microscopy and immunocytochemistry using a calcitonin antiserum. Electron microscopy confirmed the presence of C-cells, containing numerous secretory granules storing calcitonin, in the luminal lining of cyst-like structures found in these glands. These cells were furnished with prominent microvillar projections at their luminal surface, and the cytoplasm of the apical region was filled with fibril material. Furthermore, the cells contained prominent junctional complexes and desmosomes at their apico-lateral surfaces. In these C-cells, secretory granules were concentrated near the lumen and some were attached to the apical cell membrane. The luminal content of the cysts had a colloid-like and flocculent appearance, and was frequently seen attached to the cytoplasmic projections or apical cell membrane of the C-cells. Since the cysts progressively increase in volume and number with age, it is suggested that they may partly play a role in the storage of excess or unneeded hormonal products.

[Seasonal variations of the ultimobranchial body of the turtle (Pseudemys scripta)]. / Sulle modificazioni cicliche stagionali del corpo ultimobranchiale di tartaruga (Pseudemys scripta).

Ultrastructural seasonal cyclic aspects of ultimobranchial body (C.U.B.) in fresh turtles (Pseudemys scripta) are studied. The C.U.B. consists of follicles and cords. The cord cells are characterized by many secretory granules measuring approximately 180 nm with variable feature and electron density. These granules are localized in the cytoplasm close to basal laminae. The follicular cells, on the contrary, present few and large secretory granules, glycogen particles, bundle of filaments and a scarcely developing Golgi apparatus and granular endoplasmic reticulum. The apical and follicular cytoplasmatic membrane is provided with small number of cilia and short microvilli. Seasonal cellular variations are described clearly in the winter (february-march) specimens of ultimobranchial body, these are characterized by more cord aspects and few follicles. The only cord cells present significant ultrastructural changes, represented by more glycogen particles, middle and wide lipid droplets and poor presecretory granules in Golgi zone. These morphological elements orient to a parallelism with the C cells of hibernant animals (Azzali 1967, Frink and Coll.) and the chief cells of parathyroid gland of the self turtle species as by our previous study.

[Calcitonin in the ultimobrancial body of Anguilla (Anguilla anguilla L.): cytologic localization by indirect immunofluorescence using human anti-salmon-calcitonin antibodies]. / Calcitonine du corps ultimobranchial d'anguilles (Anguilla anguilla L.): localisation cytologique par immunofluorescence indirecte à l'aide d'un anticorps humain anti-calcitonine de saumon.

The localization of intracellular calcitonin has been achieved by immunofluorescence in the cytoplasm of all cells forming the epithelium of the ultimobranchial body of eels, using a human antiserum against synthetic Salmon calcitonin I. The specificity of the reaction is demonstrated by inhibition with synthetic salmon calcitonin (S.C.T.); the fluorescence is not inhibited by synthetic human calcitonin (H.C.T.).

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.

Effects of vitamin A deficiency on ultimobranchial cysts in the thyroid gland: an electron microscopic study.

Ultimobranchial cysts in the thyroid glands of rats receiving a diet adequate in vitamin A are lined with stratified squamous epithelium and contain non-keratinized cellular debris. The epithelium of these cysts in vitamin A deficient animals is keratinized, and their lumina contain keratinized cellular strands surrounding a core of cellular debris. Upon return to a diet adequate in vitamin A the epithelium returns to a non-keratinized state, and the lumina contain keratinized strands surrounded by cell fragments and desquamated whole cells. Occasionally these cysts have an epithelium that is highly irregular in appearance. The relationship of alterations in this tissue to possible subsequent development of neoplasias is discussed.

Fine structure of the ultimobranchial cysts in the thyroid of the adult guinea pig.

The ultimobranchial cysts in the thyroid of the adult guinea pig are identified by a cytochemical method. The ultimobranchial tissue has the shape of an irregular cyst, with non-specific esterase activity that is resistent to HgCl2 inhibition. The TEM reveals five different types of epithelial cell in the cyst wall: 1. cells with deeply invaginated nuclei and of varying shape, from flat to cylindrical but most of them cuboidal. 2. Mucous cells that are tall and similar to goblet cells. 3. Tall cells with big granules that have a dense core. 4. Ciliated cells similar to those in the respiratory tract. 5. C-cells crowded with the small dense granules typical for the cell type. The cyst is enveloped by rather coarse collagen fibers and many wide sinusoids.

Cilia-forming potentials of endocrine organs originating from the foregut.

Cilia were found in intracellular localizations or on the surface of certain cells of frog thymus and chicken parathyroid gland and ultimobranchial body. The experimental observations suggest that ciliogenesis is probably a general property of branchiogenic epithelium, which either persists, or can be activated by certain influences after the functional differentiation of endocrine organs arising from the foregut.

Structure of rat ultimobranchial bodies after birth.

The evolution of ultimobranchial bodies in Holtzman rats during the first 64 weeks after birth was studied by reconstructing three-dimensional models from serial sections stained by the periodic acid-Schiff technique.Radio-autography with 125I was made to see if ultimobranchial cells and/or follicular cells lining the lumen of mixed follicles were able to iodinate proteins. The term ultimobranchial body designates herein an embryonic vesicular structure (derived from the third pharyngeal pouch) whose wall is made of stratified squamous epithelium. During the first week after birth, the vesicular ultimobranchial body elongates rapidly and becomes a canal or a duct. During the second week, cell desquamation brings about local dilatations in the lumen of these ducts; with further enlargement ultimobranchial follicles will appear. In one-day-old rats, mixed follicles are present. Only the follicular component of mixed follicles iodinates proteins as is shown by radioautography. The reconstructed models enlarge rapidly up to the 56th day after birth at which time their weight has increased nineteenfold. These same models show that the three morphological components of ultimobranchial parenchyma, namely ducts, follicles and mixed follicles, are in continuity within the thyroid parenchyma. The formation of new thyroid follicles after birth and the possiblility that the ultimobranchial parenchyma may function as an endocrine gland of holocrine type are discussed.