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

Diverse contribution of amniogenic somatopleural cells to cardiovascular development: With special reference to thyroid vasculature

BACKGROUND

The somatopleure serves as the primordium of the amnion, an extraembryonic membrane surrounding the embryo. Recently, we have reported that amniogenic somatopleural cells (ASCs) not only form the amnion but also migrate into the embryo and differentiate into cardiomyocytes and vascular endothelial cells. However, detailed differentiation processes and final distributions of these intra-embryonic ASCs (hereafter referred to as iASCs) remain largely unknown.

RESULTS

By quail-chick chimera analysis, we here show that iASCs differentiate into various cell types including cardiomyocytes, smooth muscle cells, cardiac interstitial cells, and vascular endothelial cells. In the pharyngeal region, they distribute selectively into the thyroid gland and differentiate into vascular endothelial cells to form intra-thyroid vasculature. Explant culture experiments indicated sequential requirement of fibroblast growth factor (FGF) and vascular endothelial growth factor (VEGF) signaling for endothelial differentiation of iASCs. Single-cell transcriptome analysis further revealed heterogeneity and the presence of hemangioblast-like cell population within ASCs, with a switch from FGF to VEGF receptor gene expression.

CONCLUSION

The present study demonstrates novel roles of ASCss especially in heart and thyroid development. It will provide a novel clue for understanding the cardiovascular development of amniotes from embryological and evolutionary perspectives.

Morphological, histological and ultra-structural studies on the ultimobranchial body of goat (Capra hircus)

Ultimobranchial body (UBB) remnant was considered as an enigma till the last few years, then it was recognized as a necessary organ where it is the origin of the parafollicular cells. The samples were fixed and processed for the histological and electron microscopic examination. Macroscopically, the UBB remnant appeared as a white mass at the end of the cranial one-third of the thyroid lobe. It was composed of solid cell nest, cluster of cells and small thyroid follicles. Transmission electron microscope showed some round cells containing euchromatic nuclei, numerous parafollicular cells with darkly stained granules and paler ones. It also showed some mast cells with heterochromatic nuclei and large darkly stained granules. The parafollicular cells were distributed throughout the thyroid gland but concentrated within the UBB remnant. To our knowledge, our findings represent very unique histological manifestations specially the ultra-structural ones which revealed an original finding about the new clear type of cells suggested to be a UBB remnant and ensure those of the light microscope.

Development of Functional Thyroid C Cell-like Cells from Human Pluripotent Cells in 2D and in 3D Scaffolds

Medullary thyroid carcinoma contributes to about 3–4% of thyroid cancers and affects C cells rather than follicular cells. Thyroid C cell differentiation from human pluripotent stem cells has not been reported. We report the stepwise differentiation of human embryonic stem cells into thyroid C cell-like cells through definitive endoderm and anterior foregut endoderm and ultimobranchial body-like intermediates in monolayer and 3D Matrigel culture conditions. The protocol involved sequential treatment with interferon/transferrin/selenium/pyruvate, foetal bovine serum, and activin A, then IGF-1 (Insulin-like growth factor 1), on the basis of embryonic thyroid developmental sequence. As well as expressing C cell lineage relative to follicular-lineage markers by qPCR (quantitative polymerase chain reaction) and immunolabelling, these cells by ELISA (enzyme-linked immunoassay) exhibited functional properties in vitro of calcitonin storage and release of calcitonin on calcium challenge. This method will contribute to developmental studies of the human thyroid gland and facilitate in vitro modelling of medullary thyroid carcinoma and provide a valuable platform for drug screening.

Comparative morphological and molecular studies on the oxygen-chemoreceptive cells in the carotid body and fish gills

Oxygen-chemoreceptive cells play critical roles for the respiration control. This review summarizes the chemoreceptive cells in the carotid body and fish gills from a morphological and molecular perspective. The cells synthesize and secrete biogenic amines, neuropeptides, and neuroproteins and also express many signaling molecules and transcription factors. In mammals, birds, reptiles, and amphibians, the carotid body primordium is consistently formed in the wall of the third arch artery which gives rise to the common carotid artery and the basal portion of the internal carotid artery. Consequently, the carotid body is located in the carotid bifurcation region, except birds in which the organ is situated at the lateral side of the common carotid artery. The carotid body receives branches of the cranial nerves IX and/or X dependent on the location of the organ. The glomus cell progenitors in mammals and birds are derived from the neighboring ganglion, i.e., the superior cervical sympathetic ganglion and the nodose ganglion, respectively, and immigrate into the carotid body primordium, constituting a solid cell cluster. In other animal species, the glomus cells are dispersed singly or forming small cell groups in intervascular stroma of the carotid body. In fishes, the neuroepithelial cells, corresponding to the glomus cells, are distributed in the gill filaments and lamellae. All oxygen-chemoreceptive cells sensitively respond to acute or chronic hypoxia, exhibiting degranulation, hypertrophy, hyperplasia, and upregulated expression of many genes.

Unraveling the Complex Interplay Between Transcription Factors and Signaling Molecules in Thyroid Differentiation and Function, From Embryos to Adults

Thyroid differentiation of progenitor cells occurs during embryonic development and in the adult thyroid gland, and the molecular bases of these complex and finely regulated processes are becoming ever more clear. In this Review, we describe the most recent advances in the study of transcription factors, signaling molecules and regulatory pathways controlling thyroid differentiation and development in the mammalian embryo. We also discuss the maintenance of the adult differentiated phenotype to ensure the biosynthesis of thyroid hormones. We will focus on endoderm-derived thyroid epithelial cells, which are responsible for the formation of the thyroid follicle, the functional unit of the thyroid gland. The use of animal models and pluripotent stem cells has greatly aided in providing clues to the complicated puzzle of thyroid development and function in adults. The so-called thyroid transcription factors - Nkx2-1, Foxe1, Pax8 and Hhex - were the first pieces of the puzzle identified in mice. Other transcription factors, either acting upstream of or directly with the thyroid transcription factors, were subsequently identified to, almost, complete the puzzle. Among them, the transcription factors Glis3, Sox9 and the cofactor of the Hippo pathway Taz, have emerged as important players in thyroid differentiation and development. The involvement of signaling molecules increases the complexity of the puzzle. In this context, the importance of Bmps, Fgfs and Shh signaling at the onset of development, and of TSH, IGF1 and TGFβ both at the end of terminal differentiation in embryos and in the adult thyroid, are well recognized. All of these aspects are covered herein. Thus, readers will be able to visualize the puzzle of thyroid differentiation with most - if not all - of the pieces in place.

The ventral peptidergic system of the adult ascidian Ciona robusta (Ciona intestinalis Type A) insights from a transgenic animal model

Ascidians are the sister group of vertebrates and occupy a critical position in explorations of the evolution of the endocrine and nervous systems of chordates. Here, we describe the complete ventral peptidergic system in adult transgenic Ciona robusta (Ciona intestinalis Type A) which expresses the Kaede reporter gene driven by the prohormone convertase 2 (PC2) gene promoter. Numerous PC2 promoter-driven fluorescent (Kaede-positive) non-neural cells were distributed in the blood sinus located at the anterior end of the pharynx, suggesting the acquisition of a peptidergic circulatory system in Ciona. Kaede-positive ciliated columnar cells, rounded cells, and tall ciliated cells were observed in the alimentary organs, including the endostyle, pharynx, esophagus, stomach, and intestine, suggesting that digestive functions are regulated by multiple peptidergic systems. In the heart, Kaede-positive neurons were located in the ring-shaped plexus at both ends of the myocardium. Nerve fiber-like tracts ran along the raphe and appeared to be connected with the plexuses. Such unique structures suggest a role for the peptidergic system in cardiac function. Collectively, the present anatomic analysis revealed the major framework of the ventral peptidergic system of adult Ciona, which could facilitate investigations of peptidergic regulation of the pharynx, endostyle, alimentary tissues, and heart.

Follicular cell lineage in persistent ultimobranchial remnants of mammals

It has been a subject of much debate whether thyroid follicular cells originate from the ultimobranchial body, in addition to median thyroid primordium. Ultimobranchial remnants are detected in normal dogs, rats, mice, cattle, bison and humans and also in mutant mice such as Eya1 homozygotes, Hox3 paralogs homozygotes, Nkx2.1 heterozygotes and FRS2α^2F/2F. Besides C cells, follicular cell lineages immunoreactive for thyroglobulin are located within these ultimobranchial remnants. In dogs, the C cell complexes, i.e., large cell clusters consisting of C cells and undifferentiated cells, are present together with parathyroid IV and thymus IV in or close to the thyroid lobe. In addition, follicular cells in various stages of differentiation, including follicular cell groups and primitive and minute follicles storing colloid, are intermingled with C cells in some complexes. This review elaborates the transcription factors and signaling molecules involved in folliculogenesis and it is supposed why the follicular cells in the ultimobranchial remnants are sustained in immature stages. Pax8, a transcription factor crucial for the development of follicular cells, is expressed in the fourth pharyngeal pouch and the ultimobranchial body in human embryos. Pax8 expression is also detected in the ultimobranchial remnants of Eya1 and Hes1 null mutant mice. To determine whether the C cells and follicular cells in the ultimobranchial remnants consist of dual lineage cells or are derived from the common precursor, the changes of undifferentiated cells in dog C cell complexes are examined after chronically induced hypercalcemia or antithyroid drug treatment.