Types Of Intercellular Junctions Research Articles

Passing across the blood-brain barrier in glioblastoma multiforme (GBM)

Introduction and purpose: Blood-brain barrier (BBB) consists of capillary endothelium, in which there are three types of intercellular junctions - adherent, tight and gap junctions.Efficient therapy involves delivering a therapeutic dose of drug into a specific site in the body, and maintaining this dose for adequate time afterwards. The aim of this study is to review current knowledge of new strategies in drug delivery to CNS and the effectiveness of these methods in glioblastoma multiforme (GBM) treatment. This review was performed using the PubMed database. A brief description of the state of knowledge: Methods for delivering drugs to the brain are divided into invasive and non-invasive. Invasive methods involve temporary disrupting tight intercellular junctions of the vascular endothelial cells and delivering drugs intracerebrally or intraventricularly during neurosurgical procedures. In recent years, there has been a growing interest in the use of nanoparticles as drug carriers to the central nervous system via blood-brain barrier. The usage of nanoparticles implies many advantages, such as non-invasive, low cost, good biodegradability, stability, ability to carry various types of agents, selectivity and ability to control drug release. Conclusions: Limited options in treating brain located tumors, including glioblastoma multiforme, due to difficulties in drug penetration through the BBB engages scientists to search for new treatments. Crossing the BBB using invasive methods based on interruption of cell junctions show promising results, but they are associated with i.a. a high risk of uncontrolled influx of toxins to the CNS or ion-electrolyte imbalance, which may lead to neuronal dysfunction. Invasive methods can be effective only in tumors, while treatment of diseases such as Alzheimer’s disease is impossible. Recent studies show that nanoparticles would be a great, non-invasive alternative, but they are difficult to use with relatively low permeability through undamaged BBB. In some studies using nanoparticles as nanocarriers (EDVDox) or SYMPHONY method (combining photothermal therapy with GNS and immunotherapy of checkpoints in a mouse model) against GBM shows positive results. More research is required to confirm the effectiveness and safety of these treatments.

Fine structure of the cardiac muscle cells in the orb-web spider Nephila clavata

The fine structural characteristics of cardiac muscle cells and its myofibril organization in the orb web spider N. clavata were examined by transmission electron microscopy. Although myofibril striations are not remarkable as those of skeletal muscles, muscle fibers contain multiple myofibrils, abundant mitochondria, extensive sarcoplasmic reticulum and transverse tubules (T-tubules). Myofibrils are divided into distinct sarcomeres defined by Z-lines with average length of 2.0 μm, but the distinction between the A-band and the I-bands is not clear due to uniform striations over the length of the sarcomeres. Dyadic junction which consisted of a single T-tubule paired with a terminal cisterna of the sarcoplasmic reticulum is found mainly at the A-I level of sarcomere. Each cell is arranged to form multiple connections with neighboring cells through the intercalated discs. These specialized junctions include three types of intercellular junctions: gap junctions, fascia adherens and desmosomes for heart function. Our transmission electron microscopy (TEM) observations clearly show that spider’s cardiac muscle contraction is controlled by neurogenic rather than myogenic mechanism since each cardiac muscle fiber is innervated by a branch of motor neuron through neuromuscular junctions.

Desmosomes: Essential contributors to an integrated intercellular junction network.

The development of adhesive connections between cells was critical for the evolution of multicellularity and for organizing cells into complex organs with discrete compartments. Four types of intercellular junction are present in vertebrates: desmosomes, adherens junctions, tight junctions, and gap junctions. All are essential for the development of the embryonic layers and organs as well as adult tissue homeostasis. While each junction type is defined as a distinct entity, it is now clear that they cooperate physically and functionally to create a robust and functionally diverse system. During evolution, desmosomes first appeared in vertebrates as highly specialized regions at the plasma membrane that couple the intermediate filament cytoskeleton at points of strong cell–cell adhesion. Here, we review how desmosomes conferred new mechanical and signaling properties to vertebrate cells and tissues through their interactions with the existing junctional and cytoskeletal network.

Cadherins in islet β-cells: more than meets the eye.

In 1975, Orci et al. (1) reported that human islet cells contain specialized membrane domains that are compatible with the ultrastructural features of two types of intercellular junctions: tight junctions and gap junctions. Since then, numerous reports have demonstrated critical functions for these cell–cell junctional complexes in islet cells (2–8). Eventually, a number of proteins were identified that regulated cell aggregation, islet cell–type segregation, architectural organization within islets of Langerhans, and state of differentiation, cell growth, and hormone secretion (9–16). Hints that direct islet cell-to-islet cell interactions are required for proper insulin secretion were uncovered in the 1980s when it was observed that single (isolated) β-cells are unresponsive to glucose unless they are given the opportunity to reaggregate into small clusters (17). Even more interesting, it was observed that islet cell types harbor specific cell-to-cell recognition signatures that drive their reaggregation into organoids that have architectural organization indistinguishable from that of native islets (18). These earlier observations have inspired numerous investigations that have led to a more complete understanding of mechanisms regulating islet cell development, architectural organization, and function. In a time of considerable interest in the development of cell-based replacement therapies for diabetes, lessons learned over the past three decades on the function of cell adhesion molecules in islet cells harbor significant translational implications. Hence, promoting the function of select members of the cadherin and integrin families of adhesion receptors …

Human chorionic gonadotropin controls luteal vascular permeability via vascular endothelial growth factor by down-regulation of a cascade of adhesion proteins

To study the functional interactions of junctional proteins acting as regulators of vascular permeability in the human corpus luteum. We investigated the role of vascular endothelial (VE)-cadherin, nectin 2, and claudin 5 as controllers of vascular endothelial cell permeability. Performing immunohistochemical dual staining, we colocalized the above-mentioned proteins in the human corpus luteum. Not applicable. Not applicable. Not applicable. Using a granulosa-endothelial coculture system, we revealed that hCG-treatment down-regulates VE-cadherin, nectin 2, and claudin 5 in endothelial cells via vascular endothelial growth factor (VEGFA). Furthermore, the interaction of VE-cadherin, nectin 2, and claudin 5 was investigated by silencing these proteins that perform siRNA knockdown. Interestingly, knockdown of VE-cadherin and claudin 5 induced a decrease of the respective other protein. This down-regulation was associated with changed rates of vascular permeability: hCG induced a VEGFA-dependent down-regulation of VE-cadherin, nectin 2, and claudin 5, which increased the endothelial permeability in the coculture system. Furthermore, knockdown of VE-cadherin, nectin-2, and claudin 5 also resulted in a consecutive increase of endothelial permeability for each different protein. These results demonstrate for the first time that VE-cadherin, nectin 2, and claudin 5 are involved in the regulation of vascular permeability in a mutually interacting manner, which indicates their prominent role for the functionality of the human corpus luteum.

Tight junctions in epidermis: from barrier to keratinization

Tight junctions (TJs) are one type of intercellular junction. TJs prevent diffusion of solutes through the intercellular spaces in simple and stratified epithelia. Mice lacking claudin-1 (an adhesion molecule at TJs) show dehydration from the skin by impaired barrier function of epidermal TJs. Meanwhile, a human hereditary disease with ichthyosis (NISCH syndrome) has been found to be a claudin-1-deficient disease. The two models of lacking-claudin-1 indicate that TJs are related not only to the epidermal barrier but also to keratinization. Research of TJs in epidermis is reviewed in view of the barrier to keratinization.

Adherens junction proteins in glomerular podocytes of quail kidney

Avian kidney glomerular filtration rate linearly relates to body mass, but glomeruli (diameter, μm) vary in size from small (12–15) to large (25–30). Intercellular junctions of glomerular podocytes are important for filtration function, but their localization and properties, especially those of adherens junctions (AJs), are not well characterized in birds. Quail glomeruli contain podocytes with numerous foot processes and slit diaphragms. We investigated whether glomerular podocytes of Japanese quail, Coturnix japonica (3–12 wks of age), express AJ proteins. We found: 1) podocin, N‐cadherin and alpha‐ and beta‐catenins are prominent in fractions from isolated glomeruli (immunoblot analysis) and are localized along glomerular capillary walls (immunofluorescence microscopy); 2) quail podocytes have at least two types of intercellular junction, slit diaphragms and junctions with close contact (electron microscopy); and 3) in both junction types, significant accumulations of immunogold particles for N‐cadherin and alpha/beta‐catenins are visualized. The results suggest that podocyte intercellular junctions have AJ properties and that they may play a role in supporting the glomerular capillary wall against high intraglomerular pressure. (Grant‐in‐Aid for Scientific Research from the Japanese Ministry for Education, Science, and Culture 21591021 to Yaoita and 21390307 to Nishimura)

Cell-Cell Adhesion in the Prelaminar Region of the Optic Nerve Head: A Possible Target for Ionic Stress

Purpose: This paper aims to study the anterior surface of the optic nerve in relation to its ability to support a source of stress acting from the vitreous cavity. The intercellular junctions of the lining astrocytes mediated by cellular adhesion molecules (CAMs) may be the main targets for ionic stress. Methods: The optic nerve of the domestic pig was prepared for light, confocal laser and transmission electron microscopy. Immunostaining was performed for antibodies against glial fibrillary acidic protein, neural cadherin (N-cadherin) and neural CAM (N-CAM). Results: Only 1 type of intercellular junction was found among the bordering astrocytes, which was characterized as a zonula adherens. Unions between lining cells showed a positive immunogold effect and immunofluorescence against N-cadherin in the zonula adherens and membrane apposition. N-CAM was also present in areas of nonjunctional cellular adhesion. Conclusion: The stability of intercellular junctions of the nerve-vitreous boundary is sensitive to altered concentrations of Ca²⁺. Since aqueous humor has half the Ca²⁺ concentration of plasma, any contact of aqueous humor with the optic nerve head can interfere with the ionic concentration of calcium in the extracellular spaces. This mechanism may contribute to age-related changes and some types of glaucoma.

Role of cell adhesion molecule nectin‐3 in spermatid development

Seminiferous epithelia of the testes contain two types of intercellular junctions: Sertoli-Sertoli junctions and Sertoli-spermatid junctions. The former junctions are equipped with tight and adherens junctions while the latter junctions are not. Ca2+ -independent immunoglobulin-like cell-cell adhesion molecules, nectin-2 and nectin-3, asymmetrically localize at the Sertoli cell side and at the spermatid side of Sertoli-spermatid junctions, respectively. They heterophilically trans-interact to make contact between the two cells. Nectin-2(-/-) mice have shown male-specific infertility, disrupted Sertoli-spermatid junctions and morphologically impaired spermatid development. Here we report testicular phenotypes of nectin-3(-/-) mice exhibiting male-specific infertility. Nectin-3(-/-) mice had defects in the later steps of sperm morphogenesis including distorted nuclei and abnormal distribution of mitochondria, as well as in localization of nectin-2 at the Sertoli-spermatid junctions. Transplantation of wild-type spermatogenic stem cells into the nectin-3(-/-) testes partially rescued these defects in sperm morphogenesis. These results indicate that the heterophilic trans-interaction between nectin-2 and nectin-3 is essential for the formation and maintenance of Sertoli-spermatid junctions that plays a critical role in spermatid development.

Ultrastructure of preimplantation genetic diagnosis-derived human blastocysts grown in a coculture system after vitrification

To evaluate ultrastructural features of preimplantation genetic diagnosis (PGD) blastocysts before and after vitrification. Descriptive study of both vitrified and fresh hatching blastocysts. PGD program at the Instituto Universitario, Instituto Valenciano de Infertilidad. Patients undergoing PGD donated their abnormal embryos for research (n = 26). Biopsied embryos were cultured in the presence of human endometrial cells until day 6. Sixteen blastocysts were vitrified. A total of 11 high-scored hatching blastocysts, 6 warmed and 5 fresh, were fixed for ultrastructure. The cytoskeleton structure, type of intercellular junctions, and basic intracellular organelles in trophoectoderm cells and the inner cell mass were analyzed. Ten of 16 blastocysts (62%) survived the warming process. Six of these showed no signs of cell degeneration and light microscopy revealed similar ultrastructural characteristics to those of controls. However, in trophoectoderm cells from both fresh and cryopreserved blastocysts, a reduced number of tight junctions and the presence of degradation bodies were detected. The particular ultrastructural features observed in PGD-derived blastocysts could be related to embryo manipulation and culture conditions. Vitrification does not seem to alter blastocysts, as those that survive hatching do not display detectable cellular alterations when observed through electron microscopy.

Endothelial cell-cell adhesion and mechanosignal transduction.

Recent reports indicate that in addition to proteins that form various types of intercellular junctions, a considerable number of proteins are localized to the area of endothelial cell-cell association. Many of these are signaling proteins, suggesting that this is an area of active signaling. In this article, we have attempted to compile a list of proteins that have been localized to the area of interendothelial association and to briefly discuss what is known about each. Since various investigators including ourselves have proposed that the region of interendothelial cell association is an important site for mechanosignaling, we will focus our discussion on the possible role of these proteins in mechanosignal transduction. We will also review the available evidence for PECAM-1 as a mechanotransducing molecule in endothelial cells.

Nectin-dependent localization of synaptic scaffolding molecule (S-SCAM) at the puncta adherentia junctions formed between the mossy fibre terminals and the dendrites of pyramidal cells in the CA3 area of the mouse hippocampus.

Two types of intercellular junctions, synaptic junctions (SJs) and puncta adherentia junctions (PAs), are observed at the synapses between the mossy fibre terminals and the dendrites of pyramidal cells in the CA3 area of the hippocampus. SJs are associated with active zones and postsynaptic densities (PSDs) where neurotransmission occurs, whereas PAs are not associated with either of them. We have found that the nectin-afadin unit as well as the N-cadherin-catenin unit localizes at the PAs and that both the units cooperatively organize the PAs. Nectins are Ca2+-independent Ig-like cell-cell adhesion molecules and afadin is a nectin- and actin filament-binding protein that connects nectins to the actin cytoskeleton. Synaptic scaffolding molecule (S-SCAM) is a neural scaffolding protein which interacts with many proteins including neuroligin, NMDA receptors, neural plakophilin-related armadillo-repeat protein/delta-catenin, a GDP/GTP exchange protein for Rap1 small G protein (PDZ-Rap-GEP), and beta-catenin. S-SCAM has been suggested to be a component of PSDs, but its precise localization at the synapses remains unknown. S-SCAM was not concentrated at the PSDs but highly concentrated and co-localized with nectins at both the sides of the PAs formed between the mossy fibre terminals and the dendrites of pyramidal cells in the CA3 area of the adult mouse hippocampus. S-SCAM co-localized with nectin-1 at the primitive synapses where the SJs and the PAs were not morphologically differentiated, and they co-localized during the maturation of the SJs and the PAs. Nectin-1 had a potency to recruit S-SCAM to the nectin-1-based cell-cell adhesion sites formed in cadherin-deficient L cells as a model system. This recruitment was dependent on the C-terminal PDZ domain-binding motif of nectin-1 which is necessary for the binding of afadin, suggesting that nectins recruit S-SCAM through afadin. Consistently, S-SCAM was co-immunoprecipitated with afadin by the anti-S-SCAM antibody from the mouse brain, but S-SCAM did not directly bind afadin. These results indicate that S-SCAM localizes at the PAs in the CA3 area of the hippocampus in a nectin-dependent manner and suggest that S-SCAM serves as a scaffolding molecule at the PAs after maturation of the synapses and at the SJs during the maturation.

Buttons and Zippers

CELL BIOLOGY Tissue organization requires the formation of specific intercellular junctions in order to create three-dimensional structures in organs and to define internal and external fluid compartments. One type of intercellular junction is known as the adherens junction, which cements neighboring cells together. Vasioukhin et al. have examined the dynamic aspects of junction formation in freshly isolated, primary cultures of epithelial cells and find that the production of junctions is a complex phenomenon involving several morphological stages. First, in response to increased extracellular calcium, each cell extrudes actin-rich projections known as filopodia; neighboring cells are drawn into close contact by these interdigitating filopodia. Then, adherens junction proteins cluster at the tips of the filopodia and serve to button cells together at these contact points. Finally, the actin cytoskeleton is reorganized to zip up the membranes of two cells along the surfaces between adherens junctions. This process provides the driving force to push the cells together tightly to form the junctional seal. Raich et al. have used time-lapse, multiphoton laser-scanning microscopy to visualize these events—extension of filopodia, recruitment of junctional proteins, and sealing of the epithelial sheet—during embryonic development of Caenorhabditis elegans. — SMH Cell 100 , 209 (2000); Curr. Biol. 9 , 1139 (1999).

Fine structure of dicyemid mesozoans, with special reference to cell junctions.

The fine structure of the dicyemid mesozoan, Dicyema acuticephalum, from Octopus vulgaris, was studied with special attention to intercellular junctional complexes between various kinds of cells. Two types of intercellular junction, namely, adherens junctions and gap junctions, were found in both vermiform stages and in infusoriform embryos. Adherens junctions were classified into two types. Zonulae adherentes-like junctions were observed between adjacent peripheral cells at vermiform stages, between adjacent external cells of infusoriform embryos, and between members of groups of internal cells that covered the urn in infusoriform embryos. Maculae adherentes-like junctions were seen between a peripheral cell and an axial cell at vermiform stages. In infusoriform embryos, these junctions were observed between various types of cells, excluding urn cells. Gap junctions were found between adjacent peripheral cells at vermiform stages, whereas in infusoriform embryos these junctions were located between various types of cells excluding urn cells. Dicyemids might be the most primitive multicellular animals to possess these basic types of cell junctions. Ciliary rootlet systems at vermiform stages and in infusoriform embryos were unique in structure compared with those of other primitive multicellular animals. J Morphol 231:297-305, 1997. © 1997 Wiley-Liss, Inc.

Desmoplakin expression and organization at human umbilical vein endothelial cell-to-cell junctions.

Desmoplakin is an intracellular component of desmosomes which plays a role in the anchorage of intermediate filaments to these structures. We report here that, despite the absence of desmosomes, cultured endothelial cells from human umbilical vein express desmoplakin I and II both at mRNA and protein level. Desmoplakin I/II are found only in the detergent insoluble fraction suggesting that most of the protein is linked to the cytoskeleton. Desmoplakin I/II could be detected by western blot only in long confluent cells even if desmoplakin mRNA levels are unchanged by cell confluency. This suggests that desmoplakin might be stabilized at protein level by its association with junctional components. Immunofluorescence confocal microscopy showed that desmoplakin codistributes with VE-cadherin and plakoglobin along the lateral cell membrane. In contrast, desmoplakin localization was distinct from that of PECAM, an endothelial specific junctional protein localized outside adherence junctions. Endothelial cells do not have keratins but they express vimentin. In confluent cells vimentin forms peripheral filaments which attach to the cell membrane in areas at desmoplakin localization. These data suggest that desmoplakin may participate in the molecular organization of interendothelial junctions by interacting with VE-cadherin and promoting vimentin anchorage. This new type of intercellular junction seems to correspond to the "complexus adhaerentes' described in vivo in lymphatic endothelium.

Heterogeneity within populations of recombinant Chinese hamster ovary cells expressing human interferon‐γ

The Chinese hamster ovary (CHO) cell line has great commercial importance in the production of recombinant human proteins, especially those for therapeutic use. Much attention has been paid to CHO cell population physiology in order to define factors affecting product fidelity and yield. Such studies have revealed that recombinant proteins, including human interferon-gamma (IFN-gamma), can be heterogeneous both in glycosylation and in proteolytic processing. The type of heterogeneity observed depends on the growth physiology of the cell population, although the relationship between them is complex. In this article we report results of a cytological study of the CHO320 line which expresses recombinant human IFN-gamma. When grown in suspension culture, this cell line exhibited three types of heterogeneity: (1) heterogeneity of the production of IFN-gamma within the cell population, (2) heterogeneity of the number of nuclei and mitotic spindles in dividing cells, and (3) heterogeneity of cellular environment. The last of these arises from cell aggregates which form in suspension culture: Some cells are exposed to the culture medium; others are fully enclosed within the mass with little or no direct access to the medium. Thus, live cells producing IFN-gamma are heterogeneous in their environment, with variable access to O(2) and nutrients. Within the aggregates, it appears that live cells proliferate on a dead cell mass. The layer of live cells can be several cells deep. Specific cell-cell attachments are observed between the living cells in these aggregates. Two proteins, known to be required for the formation of certain types of intercellular junctions, spectrin and vinculin, have been localized to the regions of cell-cell contact. The aggregation of the cells appears to be an active process requiring protein synthesis. (c) 1995 John Wiley & Sons, Inc.

Junctions between early developing osteoblasts of rat calvaria as revealed by freeze-fracture and ultrathin section electron microscopy.

Although intercellular junctions have been described between mature lamellar bone cells, little has been known about junctions between osteoblasts in early developing bone. We therefore conducted a freeze-fracture and ultrathin section study on developing calvaria of rat embryos aged 17-19 days to determine what types of intercellular junctions appear between osteoblasts in early osteogenesis. We observed that three main types of junctional structures, i.e., adherens of the macular type, gap, and focal tight junctions, coexist between osteoblasts in early developing bone. Their possible involvement in early morphogenetic events is discussed. Tight junctions are considered to be involved in compartmentalization of the early matrix and final polarization of osteoblasts.

Gap junction alterations in the failing heart.

Electrical and mechanical integration between myocytes is mediated by three types of intercellular junction, the fascia adherens, desmosome and gap junction. Gap junctions are responsible for electrical coupling, and consist of clusters of plasma membrane channels that directly link the cytoplasmic compartments of neighbouring cells. Each channel consists of two hemichannels (connexons; one from each plasma membrane) aligned across the narrow extracellular gap, and each hemichannel is constructed from six connexin molecules. Using specific anticonnexin43 antibodies for immunofluorescence localization in combination with confocal laser scanning microscopy, alterations in the expression of connexin43 gap junctions have been investigated in chronic ischaemic heart disease and heart failure due to ischaemic cardiomyopathy. Two major alterations are apparent: (1) disturbance in the spatial distribution of gap junctions at the border zone of healed infarcts, and (2) reduction in the quantity of immunodetectable connexin43 in regions of normal gap junction distribution distant from infarct scars. These changes are likely to contribute to electromechanical dysfunction in ischaemic heart disease and heart failure, and appear to form part of a wider pattern of altered expression of different connexin types in the diseased heart.

Structure of the subgenual organ in the green lacewing, Chrysoperla carnea

REM and TEM studies of the subgenual organ in Chrysoperla carnea (Neuroptera: Chrysopidae) show that it is composed of three scolopidia, each with one sensory, one scolopale and one cap cell. The distal part of the dendrite shows a cilium with a ‘9 + 0’ structure. The cross-handing pattern of the ciliary root has a periodicity of bands of about 61 nm. The scolopale material in a certain part of the scolopale cell is organized into five rods. The cell bodies of all three cap cells form a lens-like structure. the velum, which is fixed to the leg wall and the trachea with an extracellular material. The importance of the velum is discussed. Four types of intercellular junction are found; spot desmosomes. belt desmosomes, septate junctions and gap junctions.

Epithelial cells retain junctions during mitosis.

It has long been known that cells show reduced cell-substratum adhesion during mitosis in tissue culture, but it is not generally known whether cell-cell adhesion is also reduced. Epithelial cells, both in culture and in tissues, are linked together by several different types of intercellular junctions. Are these junctions disassembled when epithelial cells divide? Cultured epithelial cells were fluorescently stained for desmosomes, tight junctions and zonulae adherentes, and large numbers of dividing cells examined by light microscopy. The results suggested that all three types of intercellular junctions were retained throughout cell division and no evidence for internalization of junctions was obtained. The persistence of intercellular junctions by cultured cells during division was confirmed by electron microscopy. In order to determine whether intercellular junctions were similarly retained by dividing cells in tissues, human colonic mucosal crypt cells and basal keratinocytes were studied by electron microscopy. Both cell types retained intercellular junctions during division. Dividing basal keratinocytes also possessed hemidesmosomal contact with the basement membrane. It is suggested that retention of cellular junctions during division is important for maintenance of tissue integrity and organization.