Mitosis in thyroid follicular epithelial cells in vivo. III. Cytokinesis

COVID-19 associated thyroid dysfunction and other comorbidities and its management using phytochemical-based therapeutics: a natural way

The present severe acute respiratory syndrome-2 (SARS-CoV-2) mediated Coronavirus pandemic (COVID-19) and post-COVID-19 complications affect human life drastically. Patients who have been cured of COVID-19 infection are now experiencing post-COVID-19 associated comorbidities, which have increased mortality rates. The SARS-CoV-2 infection distresses the lungs, kidneys, gastrointestinal tract, and various endocrine glands, including the thyroid. The emergence of variants which includes Omicron (B.1.1.529) and its lineages threaten the world severely. Among different therapeutic approaches, phytochemical-based therapeutics are not only cost-effective but also have lesser side effects. Recently a plethora of studies have shown the therapeutic efficacy of various phytochemicals for the treatment of COVID-19. Besides this, various phytochemicals have been found efficacious in treating several inflammatory diseases, including thyroid-related anomalies. The method of the phytochemical formulation is quick and facile and the raw materials for such herbal preparations are approved worldwide for human use against certain disease conditions. Owing to the advantages of phytochemicals, this review primarily discusses the COVID-19-related thyroid dysfunction and the role of key phytochemicals to deal with thyroid anomaly and post-COVID-19 complications. Further, this review shed light on the mechanism via which COVID-19 and its related complication affect organ function of the body, along with the mechanistic insight into the way by which phytochemicals could help to cure post-COVID-19 complications in thyroid patients. Considering the advantages offered by phytochemicals as a safer and cost-effective medication they can be potentially used to combat COVID-19-associated comorbidities.

Complete dissipation of coherent clonal growth occurs before gastrulation in mouse epiblast

Observations on chimaeric mice argue that there must be considerable dispersal and intermingling of the clonal descendants of epiblast founder cells at an early stage in the development of the tissue. However, it has not been established when or how this occurs. Here we have used a genetic marker that enables donor cells to be visualized in situ to examine the early postimplantation distribution of clones obtained by transplanting epiblast founder cells into host blastocysts. We have also determined the spatial relationship between sister cells in non-chimaeric postimplantation epiblast by ionophoretic injection of a fluorescent macromolecule. Both experimental approaches support the conclusion that breakdown of coherent clonal growth accompanies epithelialization of the epiblast and is essentially complete by the onset of gastrulation. Furthermore, the clonal analysis shows that descendants of different epiblast founder cells continue to intermingle extensively well into organogenesis. We suggest that this sustained intermingling of cells in the epithelial epiblast, which does not occur in the adjacent visceral endoderm, depends on cells losing contact with the basal lamina when they divide. These findings have implications both for patterning of the early amniote embryo and for the growth of tall columnar epithelia in general.

Chromosomal proteins and cytokinesis: patterns of cleavage furrow formation and inner centromere protein positioning in mitotic heterokaryons and mid-anaphase cells

After the separation of sister chromatids in anaphase, it is essential that the cell position a cleavage furrow so that it partitions the chromatids into two daughter cells of roughly equal size. The mechanism by which cells position this cleavage furrow remains unknown, although the best current model is that furrows always assemble midway between asters. We used micromanipulation of human cultured cells to produce mitotic heterokaryons with two spindles fused in a V conformation. The majority (15/19) of these cells cleaved along a single plane that transected the two arms of the V at the position where the metaphase plate had been, a result at odds with current views of furrow positioning. However, four cells did form an additional ectopic furrow between the spindle poles at the open end of the V, consistent with the established view. To begin to address the mechanism of furrow assembly, we have begun a detailed study of the properties of the chromosome passenger inner centromere protein (INCENP) in anaphase and telophase cells. We found that INCENP is a very early component of the cleavage furrow, accumulating at the equatorial cortex before any noticeable cortical shape change and before any local accumulation of myosin heavy chain. In mitotic heterokaryons, INCENP was detected in association with spindle midzone microtubules beneath sites of furrowing and was not detected when furrows were absent. A functional role for INCENP in cytokinesis was suggested in experiments where a nearly full-length INCENP was tethered to the centromere. Many cells expressing the chimeric INCENP failed to complete cytokinesis and entered the next cell cycle with daughter cells connected by a large intercellular bridge with a prominent midbody. Together, these results suggest that INCENP has a role in either the assembly or function of the cleavage furrow.

Orientation and three-dimensional organization of actin filaments in dividing cultured cells

The current hypothesis of cytokinesis suggests that contractile forces in the cleavage furrow are generated by a circumferential band of actin filaments. However, relatively little is known about the global organization of actin filaments in dividing cells. To approach this problem we have used fluorescence-detected linear dichroism (FDLD) microscopy to measure filament orientation, and digital optical sectioning microscopy to perform three-dimensional reconstructions of dividing NRK cells stained with rhodamine-phalloidin. During metaphase, actin filaments in the equatorial region show a slight orientation along the spindle axis, while those in adjacent regions appear to be randomly distributed. Upon anaphase onset and through cytokinesis, the filaments become oriented along the equator in the furrow region, and along the spindle axis in adjacent regions. The degree of orientation appears to be dependent on cell-cell and cell-substrate adhesions. By performing digital optical sectioning microscopy on a highly spread NRK subclone, we show that actin filaments organize as a largely isotropic cortical meshwork in metaphase cells and convert into an anisotropic network shortly after anaphase onset, becoming more organized as cytokinesis proceeds. The conversion is most dramatic on the adhering ventral surface which shows little or no cleavage activity, and results in the formation of large bundles along the equator. On the dorsal surface, where cleavage occurs actively, actin filaments remain isotropic, showing only subtle alignment late in cytokinesis. In addition, stereo imaging has led to the discovery of a novel set of filaments that are associated with the cortex and traverse through the cytoplasm. Together, these studies provide important insights into the process of actin remodeling during cell division and point to possible additional mechanisms for force generation.

Temporal changes in the expression and distribution of adhesion molecules during liver development and regeneration

We have compared by immunocytochemistry and immunoblotting the expression and distribution of adhesion molecules participating in cell-matrix and cell-cell interactions during embryonic development and regeneration of rat liver. Fibronectin and the fibronectin receptor, integrin alpha 5 beta 1, were distributed pericellularly and expressed at a steady level during development from the 16th day of gestation and in neonate and adult liver. AGp110, a nonintegrin fibronectin receptor was first detected on the 17th day of gestation in a similar, nonpolarized distribution on parenchymal cell surfaces. At that stage of development haemopoiesis is at a peak in rat liver and fibronectin and receptors alpha 5 beta 1 and AGp110 were prominent on the surface of blood cell precursors. During the last 2 d of gestation (20th and 21st day) hepatocytes assembled around lumina. AGp110 was initially depolarized on the surface of these acinar cells but then confined to the lumen and to newly-formed bile canaliculi. At birth, a marked increase occurred in the canalicular expression of AGp110 and in the branching of the canalicular network. Simultaneously, there was enhanced expression of ZO-1, a protein component of tight junctions. On the second day postpartum, presence of AGp110 and of protein constituents of desmosomes and intermediate junctions, DGI and E-cadherin, respectively, was notably enhanced in cellular fractions insoluble in nonionic detergents, presumably signifying linkage of AGp110 with the cytoskeleton and assembly of desmosomal and intermediate junctions. During liver regeneration after partial hepatectomy, AGp110 remained confined to apical surfaces, indicating a preservation of basic polarity in parenchymal cells. A decrease in the extent and continuity of the canalicular network occurred in proliferating parenchyma, starting 24 h after resection in areas close to the terminal afferent blood supply of portal veins and spreading to the rest of the liver within the next 24 h. Distinct acinar structures, similar to the ones in prenatal liver, appeared at 72 h after hepatectomy. Restoration of the normal branching of the biliary tree commenced at 72 h. At 7 d postoperatively acinar formation declined and one-cell-thick hepatic plates, as in normal liver, were observed.

Histologic changes in tissue components of the hyperplastic thyroid gland during its involution in the rat

Male Fischer rats were fed a low-iodine diet containing thiouracil for 21 days to produce hyperplastic thyroid glands, and then fed a high-iodine diet for various time intervals, from 5 hr to 180 days, in order to study the morphological changes that occur during involution. Thyroids were fixed by perfusion fixation and embedded in Epon. Sections were examined by light microscopy. Initially at 0 days of involution (at the time of the change to the high-iodine diet), follicular lumens were very narrow and capillary lumens were very wide. The capsule was thick and infiltrated with mononuclear leukocytes. No obvious changes occurred for 1 day after the change in diet, but shortly thereafter capillary lumens began to narrow. By 4 days, most capillary lumens were close to normal size; capillaries formed a more or less normal bed except that many were embedded in a relatively thick or wide interfollicular matrix. This matrix was largely gone by 21 days. Between 1 and 21 days, follicular lumens dilated progressively as colloid accumulated. The density of staining of the accumulated colloid varied from follicle to follicle, and this variation was also observed in older controls. Inflammatory cells gradually disappeared from the capsule and most were gone by 15 days. Starting at approximately 15 days and continuing to 180 days, one or more disintegrating cells were found in some lumen profiles. Colloid goiters were not observed in these rats even after several months of involution. Some lumens were rather large, however, and small fractions of the follicles, both small and large, were bounded by flat cells and resembled "cold" follicles morphologically.

Reorganization of circumferential microfilament bundles in retinal epithelial cells during mitosis

To examine the behaviour of the apical circumferential microfilament bundles (CMBs) associated with the zonula adhaerens (ZA)-junctions during mitosis, retinal pigment epithelial cells were labelled for F-actin, and retinas were serially sectioned for TEM. The results show that the ZA-CMB-complex persists throughout all stages of mitosis. At metaphase, the cells round up, but stay joined apically to adjacent cells by ZA-junctions. At telophase, the cleavage furrow forms asymmetrically from the basal end progressively toward the apical end, where the daughter cells remain connected by an intercellular bridge (IB). As the cleavage furrow with the contractile ring (CR) approaches the CMB, the two microfilament (MF) systems are oriented perpendicularly to each other. At the level of the CMB, the MFs of the CR connect the opposite sides of the CMB and bisect it into two CMBs, one for each of the two daughter cells. Subsequently, the CR in the IB splits into two, one on either side of the midbody. The two daughter cells, having acquired a complete CMB of their own, do not become direct neighbours, since adjacent cells, which remain joined to the apical ZA-junction of the dividing cell, are observed in the cleavage furrow, where they meet and form a ZA-junction between themselves, just below the IB. Separation of the daughter cells without losing contact with neighbouring cells at the level of the apical ZA-junction thus maintains the integrity of the epithelial sheet during mitosis.

An ultrastructural study of mitosis and cytokinesis in normal 'resting' human breast

The parenchyma of the normal "resting" human breast was examined by electron microscopy to characterize the cells undergoing mitosis and the mechanism by which the normal tissue architecture is maintained during this process. In this study of 112 mitotic cells, it was found that the mitotic cells were luminally positioned, polarised epithelial cells with no evidence of myoepithelial cell division. Ultrastructurally, the nuclear and cytoplasmic changes were consistent with previous reports of mitosis in other tissues. However, unlike all previous reports, two specific orientations of the nuclear spindle and thus the planes of cytokinesis were observed. In a few cases the spindle formed parallel to the lumen and division resulted in two luminally positioned daughter cells. However, in the majority of mitotic cells the spindle was approximately at right angles to the lumen and this orientation resulted in a luminally and a basally positioned daughter cell. It is proposed that the abnormally positioned basal daughter cell could develop into a myoepithelial cell or undergo deletion (apoptosis). Thus the two orientations of mitosis may explain the mechanism by which the epithelial and myoepithelial cell populations were maintained by a single progenitor cell without disrupting the integrity of the tissue architecture.

Selective electronmicroscopical contrast of the ring canals joining germ cells by ethanolic phosphotungstic acid and uranyl-EDTA-lead

The edge of ring canals joining germ cells in mouse testis show a high and selective electronmicroscopical contrast after application of ethanolic phosphotungstic acid and uranyl-EDTA-lead. The contrasting reaction of this fibrous structure, which originates from the contractile ring during previous cytokinesis, is briefly discussed.

Preservation of hepatocyte plasma membrane domains during cell division in situ in regenerating rat liver

We have utilized antibodies against five domain-specific integral proteins of the rat hepatocyte plasma membrane to examine the fates of the plasma membrane domains during hepatocyte division in the regenerating rat liver. The proteins were quantified on immunoblots of liver homogenates prepared during the peak of hepatocyte mitotic activity, 28-30 hr after two-thirds hepatectomy. Two sinusoidal/lateral proteins, CE 9 and the asialoglycoprotein receptor, and one bile canalicular protein, dipeptidylpeptidase IV, were not changed significantly in amount; whereas one sinusoidal/lateral protein, the epidermal growth factor receptor, and one bile canalicular protein, HA 4, were reduced to less than or equal to 50% of control levels. Light microscopic examination of plastic sections of regenerating liver tissue revealed that the mitotic hepatocytes generally appeared to retain normal contacts with neighboring interphase hepatocytes. Immunofluorescence was used to localize the domain-specific proteins on mitotic hepatocytes identified in 0.5-micron frozen sections of 28- to 30-hr regenerating liver tissue. Independent of mitotic stage, the hepatocytes retained mutually exclusive bile canalicular and sinusoidal/lateral domains, as defined at the molecular level by the distributions of specific proteins, such as HA 4 and CE 9, respectively.

Thyrotropin preparations are mitogenic for thyroid epithelial cells in follicles in suspension culture

We have been investigating the extent to which separated thyroid follicles in suspension culture, free of endothelium and fibroblasts, have the properties of follicles in vivo. To test whether thyrotropin (TSH) can cause thyroid epithelial cells to undergo mitosis, preparations of follicles suspended in Coon's modified F-12 medium with 0.5% calf serum were incubated with 10 milliunits of impure or pure TSH per ml. Three results were obtained: (i) TSH preparations stimulated the incorporation of [3H]thymidine into cell nuclei; (ii) mitotic figures were induced and they had the same characteristic ultrastructural features as those observed in vivo; and (iii) the cell number doubled in the course of 3 days of exposure to TSH. The results suggest that TSH is a mitogen for the principal thyroid epithelial celland that other substances found in the usual impure TSH preparations are not necessary for the mitogenic activity. It can act in the absence of nonfollicular cells. The initial multiplication rates are similar to those in vivo. The cells do not have to spread to divide in contrast to the requirement for spreading in the case of fibroblasts.