Changes in the distribution of filament-containing septate junctions as coelenterate myoepithelial cells change shape

This paper describes the redistribution of septate junctions during an increase in diameter of myoepithelial cells from mesenteries of the sea anemone Metridium senile (L). Each septum was composed of a filament core, 9.5-10.2 nm in diameter, which had a double row of lateral projections from each side to the adjacent cell membrane. Septa were arranged in patches in which neighbouring septa lay parallel, 28-33 nm apart. When anaesthetized mesenteries were stretched, myoepithelial cell layers decreased from a mean of 32 to 8 micron thick; each cell shortened and its apical diameter increased. The integrity of the septate junctions was, however, maintained. The mean perimeter of septate junctions, corresponding to that of the cells, increased from 20 to 31 micron; mean depth decreased from 3.7 to 2.1 micron. There was no significant change in spacing between septa. Patches of septa, free to move in a fluid matrix of junction cell membranes, may form mobile attachment sites between cells, thus allowing those cells to change shape. Number and distribution density of microvilli decreased when cell diameter increased. This implies that the microvilli contribute membrane to the cell surface as its surface area increases. Gastrodermal cells are compared with epidermal cells that do not undergo dramatic changes in diameter.     

Quantitative measures of gastrovascular flow in octocorals and hydroids: toward a comparative biology of transport systems in cnidarians

Using microscopy, the gastrovascular systems of four hydroids (Eirene viridula, Cordylophora lacustris, Hydractinia symbiolongicarpus, and Podocoryna carnea) and two distantly related alcyonacean octocorals (Acrossota amboinensis and Sarcothelia sp.) were examined and compared within a phylogenetic framework. Despite a range of stolon widths (means 53–160 μm), the hydroid species exhibited similar patterns of gastrovascular flow: sequentially bidirectional flow in the stolons, driven by myoepithelial contractions emanating from the center of the colony. Unlike the hydroids, the gastrovascular system of A. amboinensis (mean stolon widths for 5 colonies, 0.57–1.21 mm) exhibited simultaneously bidirectional flow with incomplete, medial baffles (width 4–20 μm) separating the flow. Baffles visualized with transmission electron microscopy consisted of endoderm, mesoglea, and occasionally another layer of tissue. Mean flow rates of the gastrovascular fluid for seven stolons ranged from 125 to 275 μm s^?1, with maximum rates of 225–700 μm s^?1. In Sarcothelia sp., stolons were of comparable width (means for 13 colonies 0.55–1.4 mm) to those of A. amboinensis. These stolons, however, were divided by several partitions (width 8–25 μm), both complete and incomplete, which were spaced every 100.5±5.1 μm (mean±SE; range 27.1–283.7 μm) and appeared structurally similar to baffles. In lanes defined by these partitions, ciliary motion was visible in image sequences, and flow was unidirectional. Within a single stolon, flow moved in different directions in different lanes and changed direction by moving from lane to lane via occasional spaces between the partitions. Mean flow rates for 30 stolons ranged from 75 to 475 μm s^?1, with maximum rates of 85–775 μm s^?1. For both octocorals, flow rates of the gastrovascular fluid were not correlated with the width of the stolon lumen. While octocoral gastrovascular systems probably exhibit differences based on phylogenetic affinities, in all species studied thus far, gastrovascular flow is entirely driven by cilia, in contrast to the hydroid taxa.     

Glial cell contacts in insects: Effects of feeding on intercellular junctions

The intercellular junctions associated with the modified glial cells of the perineurium have been examined in the ganglia and main abdominal nerves of the blood-sucking bug Rhodnius prolixus, both before and and after feeding, by means of freeze-fracture and tracer studies. It was found that the pleated septate junctions found in the main abdominal nerve have many fewer septa than those found in the ganglion. These junctions appear to provide the flexibility needed for the movement of cells which occurs to accommodate the tremendous increase in body size that takes place after a bloodmeal. On feeding and during the subsequent period of digestion the nerves stretch to double their length, yet the blood-brain barrier is maintained throughout. In the same manner as loosely interconnected tight junctions, septate junctions with fewer septa seem to form a junction which is able to respond readily to the stress of stretching. With feeding and afterwards the septate junctions become disorganized and disassemble, while the gap junctions and tight junctions remain intact. It is envisaged, therefore, that the primary function of the septate junction is adhesive.     

Filipin-cholesterol complexes in plasma membranes and cell junctions of Tenebrio molitor epidermis

The polyene antibiotic filipin combines with cholesterol in membranes to form complexes that are readily identifiable in the electron microscope. The distribution of filipin-cholesterol (FC) complexes is most easily studied by freeze-fracture. Larval epidermis of Tenebrio molitor (Insecta, Coleoptera) was maintained in vitro for 48 hr, since the electrophysiological properties of the cells are best characterized under these conditions. The cells were fixed in buffered 3.0% glutaraldehyde at RT for 15 min, transferred to fresh fixative containing 1% DMSO and filipin (final concentration; 0.5 mg/ml) for 3 hr RT. Control cells were treated in fixative containing 1% DMSO only. In freeze fracture replicas, FC complexes appear on the plasma membrane as large circular protrusions measuring 26.5 +/- 6.8 nm (x +/- s.d.) n = 50, in diameter and 17.1 +/- 2.8 nm, n = 50, in height and 11.7 +/- 2.6 nm, n = 25, in depth. Protrusions are about two times more frequent on the E face while pits are several times more frequent on the P face. FC complexes are most abundant (greater than 50/mu m2) on the basal membrane surface of the cells but are excluded from regions of hemidesmosomal plaques that anchor the cells to the basal lamina. FC complexes are also abundant on the apical surfaces of the cells where cuticle secretion occurs. In the lateral regions below the junctional belt, FC complexes are less numerous but often appear to increase in frequency in a graded fashion away from the junctional region. The septate junctions are relatively free of FC complexes except in regions where they open to form islands. These islands often contain gap junctions but the FC complexes rarely invade the particle domains of the gap junctions. Single FC complexes were seen in three out of a total of 97 gap junctions. Exposure of the epidermis to 20-hydroxyecdysone for 24 hr in vitro did not induce the appearance of FC complexes within the cell junctions.     

Primary ciliogenesis is a crucial step for multiciliated cell determinism in the respiratory epithelium

The alteration of the mucociliary clearance is a major hallmark of respiratory diseases related to structural and functional cilia abnormalities such as chronic obstructive pulmonary diseases (COPD), asthma and cystic fibrosis. Primary cilia and motile cilia are the two principal organelles involved in the control of cell fate in the airways. We tested the effect of primary cilia removal in the establishment of a fully differentiated respiratory epithelium. Epithelial barrier integrity was not altered while multiciliated cells were decreased and mucous-secreting cells were increased. Primary cilia homeostasis is therefore paramount for airway epithelial cell differentiation. Primary cilia-associated pathophysiologic implications require further investigations in the context of respiratory diseases.     

The ultrastructural aspects of neoplastic myoepithelial cell in pleomorphic adenomas of salivary glands

The purpose of this study has been to establish the major ultrastructural aspects of the myoepithelial cell and the myoepithelial-like cells proliferated in the pleomorphic adenomas of salivary glands. Thus, twelve benign pleomorphic adenomas of salivary glands have been studied by electron-microscopy transmission techniques. Our analysis has proved the proliferation of two major cellular populations, one of ductal type and one of myoepithelial type, which tried to reproduce the tubulo-acinar cytoarchitecture from the normal salivary glands. We have also noticed the key role of the so-called 'modified' myoepithelial cells from the periphery of the proliferating epithelial units in the genesis of the myxoid and chondromyxoid tumoral stromal areas. All these ultrastructural aspects have explained the great histological diversity of these salivary gland neoplasms as well as the key role of the myoepithelial cell in its histogenesis.     

Adaptation of a ciliary basal apparatus to cell shape changes in a contractile epithelium

Cilia projecting from the surfaces of highly contractile myoepithelia in the sea anemone Metridium senile maintain their basal orientation, and their ability to propel water, at different states of mesentery contraction, despite substantial changes of myoepithelial cell diameter and length. The ciliary basal apparatus in each monociliated myoepithelial cell is structurally well adapted to provide a stable anchorage for the cilium whilst compensating for these shape changes. It is composed of a distal centriole (basal body), a proximal centriole, a striated rootlet 2-3 micron long which is composed of a bundle of 4-6 nm filaments, and an arched rootlet, also striated, which is composed of a relatively loose bundle of 9-11 nm filaments. A single basal foot projects from the side of the distal centriole in the same direction as the path of the cilium during an effective-stroke; its tip is a focus for many microtubules that radiate outward in all directions toward the cell membrane. The arched rootlet forms a single arch in the cell apex, also in the same plane as the path of the cilium during an effective-stroke. The central axis of the basal apparatus, that is through the distal centriole and the striated rootlet, passes through the apex of the arch. The arched rootlet is apparently flexible so that it can increase or decrease its span as the cell increases or decreases in diameter. In pharnyx and siphonoglyph cells from M. senile, which do not undergo great changes in diameter or length, there is no arched rootlet, and the striated rootlet is much longer. The broad structural diversity of the metazoan ciliary basal apparatus must to a large extent be related to the diversity of the structural and mechanical properties of the cells in which it occurs.     

Role of pleated septate junctions in the epithelium of miracidia of Schistosoma mansoni during transformation to sporocysts in vitro

The surfaces of miracidia of Schistosoma mansoni were examined ultrastructurally during in vitro transformation to sporocysts. Before transformation, the surface was composed of ciliated epithelial plates (EP) that were set into a reticulum of narrow syncytial ridges (SR). The EP were attached to SR by extensive pleated septate junctions that had 18-24 strands of intramembrane particles (IMP) on the protoplasmic faces and complementary pits on the ectoplasmic faces. These junctions also appeared to separate the EP plasma membrane into apical and basolateral domains with a larger number of IMPs on the latter. Transformation was induced by placing the miracidia in salt containing medium which also halted ciliary beating. In 2-5 hr, the SR expanded until they formed a syncytium covering the parasite surface, while the EP retracted and rounded up. During this time, the EP and SR were held in contact with one another by the septate junctions which became progressively convoluted. Subsequently, the EP detached from the parasite. When transforming miracidia were returned to fresh water, the cilia resumed beating and the EP detached from the parasite surface and exposed the underlying basement membrane. Those EP that remained attached were connected only by septate junctions to the expanded SR. These studies demonstrate that the formation of the syncytium occurs gradually with contact maintained between EP and SR via the septate junctions. Further, the septate junctions are similar to occluding junctions in mammalian epithelia since they segregate the plasma membrane of the EP and they have an adhesive function.     

Rotokinesis, a novel phenomenon of cell locomotion-assisted cytokinesis in the ciliate Tetrahymena thermophila

The mechanism responsible for final cell separation at the end of cytokinesis is currently unknown. Knockout strains of the ciliate, Tetrahymena thermophila lacking the kinesin-II homologous molecular motors, Kin1p and Kin2p are paralyzed due to their complete loss of cilia and undergo frequent cytokinesis failures. Observations of live dividing cells revealed that cleavage furrow ingression is normal in kinesin-II double knockout cells until the final stage of cell separation (Brown et al., 1999). During closer inspection of dividing cells using video differential interference contrast microscopy, we found that wild-type cells undergo an extremely complex motile behavior near the end of cytokinesis. This process, which we have named rotokinesis, appears to facilitate the physical separation of daughter cells. Here we present recent work onTetrahymena rotokinesis, and review studies in other organisms which suggest that the use of cell locomotion in the completion of cytokinesis is a general phenomenon of motile cell types.     

Cell type conversion in a mouse melanoma cell clone

Summary A melanoma cell clone was isolated from cultured B16 mouse melanoma cells. This clone,conv, which was characterized by rounded and spindle-shaped cell morphology, was not highly melanotic under the usual culture condition but had high tyrosinase (dopa oxidase) activity. When the cells were seeded to form colonies on a plastic culture dish in Eagle’s minimum essential medium supplemented with 10% bovine calf serum, two kinds of cell types always appeared. One was cytochemically dopa-positive and spindle-shaped (S type cell) with the same phenotypes as those of the parental cells. The other was dopa-negative and fibroblastlike (F type cell) containing no melanosomes. It was observed that the conversion from S type to F type occurred with a high frequency. The conversion from F type to S type also occurred but with a low frequency.     

Further studies on the junctional complex in the intestine of Sagitta setosa

Summary The intramembrane structures of the pleated septate junction which occur in the junctional complex of the intestine of the chaetognath Sagitta setosa have been investigated.The pleated septate junction is made up of linear rows of irregularly shaped and sized particles, often fused into short rods, and pits which can be fused into furrows. The distribution of these structures on E and P faces depends upon the preparative methods used. Many of the morphological characteristics are the same as those of the lower invertebrate pleated septate junction type defined by Green (1981a). The physiological significance of this junction is obscure.On the basis of the presence of septate junctions (both of the paired septate junction and pleated septate junction types) which have mainly morphological characteristics of the lower invertebrate pleated septate junction we can add to the hypothesis that chaetognaths are not related to the molluscs and arthropods.     

Establishment and characterization of a novel human myoepithelial cell line and matrix-producing xenograft from a parotid basal cell adenocarcinoma

Summary Myoepithelial cells exert important paracrine effects on epithelial morphogenesis and mitogenesis through direct cell-cell interactions and through synthesis of a basement membrane extracellular matrix. To study these effects further, this study established the first immortalized human myoepithelial cell line, HMS-1, and transplantable xenograft, HMS-X, from the rare parotid basal cell adenocarcinoma. The cell line exhibited a fully differentiated myoepithelial phenotype and the xenograft exhibited the rare property of accumulating an abundant extracellular matrix composed of both basement membrane and nonbasement membrane components with the latter predominating. With HMS-1 as a feeder layer, dramatic and specific induction of epithelial morphogenesis (sheroid formation) occurred with selected normal epithelial and primary carcinoma target cells. HMS-1 and HMS-X provide distinct advantages over the conventional murine matrices in existence. They will be invaluable in future studies of human tumor-myoepithelial and matrix interactions important for tumor cell growth, invasion, and metastasis.     

Cellulose synthesis in two secondary cell wall processes in a single cell type

Plant cells have a rigid cell wall that constrains internal turgor pressure yet extends in a regulated and organized manner to allow the cell to acquire shape. The primary load-bearing macromolecule of a plant cell wall is cellulose, which forms crystalline microfibrils that are organized with respect to a cell''s function and shape requirements. A primary cell wall is deposited during expansion whereas secondary cell wall is synthesized post expansion during differentiation. A complex form of asymmetrical cellular differentiation occurs in Arabidopsis seed coat epidermal cells, where we have recently shown that two secondary cell wall processes occur that utilize different cellulose synthase (CESA) proteins. One process is to produce pectinaceous mucilage that expands upon hydration and the other is a radial wall thickening that reinforced the epidermal cell structure. Our data illustrate polarized specialization of CESA5 in facilitating mucilage attachment to the parent seed and CESA2, CESA5 and CESA9 in radial cell wall thickening and formation of the columella. Herein, we present a model for the complexity of cellulose biosynthesis in this highly differentiated cell type with further evidence supporting each cellulosic secondary cell wall process.     

The myoepithelial cell layer may serve as a potential trigger factor for different outcomes of stage-matched invasive lobular and ductal breast cancers

Invasive lobular cancer (ILC) tends to be significantly larger in size with significantly more positive lymph nodes, whereas ILC has a significantly more favorable outcome, compared to stage-matched invasive ductal carcinoma (IDC). The mechanism accounting for such differences remains elusive. Based on morphological, immunohistochemical, and molecular studies of over 1,000 cases of human breast cancers, we hypothesize that the differences may result from the structural and/or functional differences of their surrounding myoepithelial cell layers, which dictate lobular and ductal tumor cells to follow different pathways of invasion or metastasis. The background, rationale, supportive data, and implications of our hypothesis are presented and discussed.     

Microtubules are involved in regulating body length in hydra

Little is known about how the size of an adult animal is determined and regulated. To investigate this issue in hydra, we altered the body size by surgically removing a part of the body column and/or by axial grafting, and examined changes of column length with time. When the body column was shortened it elongated and resumed the original length within 24–48 h. This increase in the body column length was not accompanied by an increase in the number of epithelial cells in the body column. Instead, each of the epithelial cells elongated longitudinally, leading to elongation of the body column. When the body column surpassed the original length, the column shortened over time. This was not accompanied by a decrease in cell number but by the shortening and thickening of the epithelial cells. TEM analysis showed that formation of microtubule arrays takes place longitudinally along the body axis in elongated cells and perpendicular to the axis in shortened cells. Treatment with a drug that degrades microtubules completely blocked changes in body length. These observations suggest that microtubules are involved in regulating the length of the hydra body column by altering the shape of the epithelial cells. We propose from these observations that hydra has a mechanism for detecting the metrical distance between the two ends of the body column.     

Differences in red cell shape of two inbred chicken lines

Summary Comparison of two inbred chicken lines (F_x > 99.9%) revealed significant differences in shape of the red blood cells (RBC). The length-width index was lower for both sexes in IC-line (1.46) when compared to CB-line chickens (1.88). Phenotypic expression of this character in F₁ hybrids and both backcross groups corresponded to the common manifestations of the metric parameters. The index in F₁ hybrid chickens deviated from intermediate values with the dominant tendency to oval RBC. An analysis of the segregating first backcross generation chickens did not show any association between RBC shape and the genotype in the blood group systems B, C, I, and D and the IgG allotypes. The differences in RBC shape were probably not associated with the survival of RBC in the blood circulation.     

Effects of membrane reference state on shape memory of a red blood cell

By using a three-dimensional continuum model, we simulate the shape memory of a red blood cell after the remove of external forces. The purpose of this study is to illustrate the effect of membrane reference state on cell behavior during the recovery process. The reference state of an elastic element is the geometry with zero stress. Since the cell membrane is composed of cytoskeleton and lipid bilayer, both the reference states of cytoskeleton (RSC) and lipid bilayer (RSL) are considered. Results show that a non-spherical RSC can result in shape memory. The energy barrier due to non-spherical RSC is determined by the ratio of the equator length to the meridian length of the RSC. Thus different RSCs can have similar energy barrier and leading to identical recovery response. A series of simulations of more intermediate RSCs show that the recovery time scale is inversely proportional to the energy barrier. Comparing to spherical RSL, a spheroid RSL contributes to the energy barrier and recovery time. Furthermore, we observe a folding recovery due to the biconcave RSL which is different from the tank treading recovery. These results may motivate novel numerical and experimental studies to determine the exact RSC and RSL.     

Wnt and planar cell polarity signaling in cystic renal disease

Cystic kidney diseases can cause end stage renal disease, affecting millions of individuals worldwide. They may arise early or later in life, are characterized by a spectrum of symptoms and can be caused by diverse genetic defects. The primary cilium, a microtubule-based organelle that can serve as a signaling antenna, has been demonstrated to have a significant role in ensuring correct kidney development and function. In the kidney, one of the signaling pathways that requires the cilium for normal development is Wnt signaling. In this review, the roles of primary cilia in relation to canonical and non-canonical Wnt/PCP signaling in cystic renal disease are described. The evidence of the associations between cilia, Wnt signaling and cystic renal disease is discussed and the significance of planar cell polarity-related mechanisms in cystic kidney disease is presented. Although defective Wnt signaling is not the only cause of renal disease, research is increasingly highlighting its importance, encouraging the development of Wnt-associated diagnostic and prognostic tools for cystic renal disease.     

Wnt and planar cell polarity signaling in cystic renal disease

Cystic kidney diseases can cause end stage renal disease, affecting millions of individuals worldwide. They may arise early or later in life, are characterized by a spectrum of symptoms and can be caused by diverse genetic defects. The primary cilium, a microtubule-based organelle that can serve as a signaling antenna, has been demonstrated to have a significant role in ensuring correct kidney development and function. In the kidney, one of the signaling pathways that requires the cilium for normal development is Wnt signaling. In this review, the roles of primary cilia in relation to canonical and non-canonical Wnt/PCP signaling in cystic renal disease are described. The evidence of the associations between cilia, Wnt signaling and cystic renal disease is discussed and the significance of planar cell polarity-related mechanisms in cystic kidney disease is presented. Although defective Wnt signaling is not the only cause of renal disease, research is increasingly highlighting its importance, encouraging the development of Wnt-associated diagnostic and prognostic tools for cystic renal disease.     

The Plasma Membrane of Myxosporidian Valve Cells: Freeze Fracture Data

Freeze fracturing of Myxosporidian spores reveals the occurrence of a continuous layer of transmembrane particles all over the surface area of the valve cells which form the spore envelope. These particles are densely packed all over the P face membrane. Due to their polygonal outline, their diameter (6-7 nm) and their central core, they resemble the particles forming the connections of gap junctions which metabolically couple the neighboring cells in animal tissues. In the present report, the role of the transmembrane particles is still hypothetical. However, they might represent a membrane structural specialization of the spores which are submitted to osmotic variations of the fluid external medium. Furthermore similar transmembrane particles are observed at the level of the septate junction which seals the valve cells. In this occurrence, they are arranged in a series of 40 double rows parallel to the suture of the spore envelope. These findings support the view that Myxosporidia are Metazoa and raise the problem of their origin.