A-CAM: a 135-kD receptor of intercellular adherens junctions. I. Immunoelectron microscopic localization and biochemical studies

Potential Therapeutic Applications of N-Cadherin Antagonists and Agonists

This review focuses on the cell adhesion molecule (CAM), known as neural (N)-cadherin (CDH2). The molecular basis of N-cadherin-mediated intercellular adhesion is discussed, as well as the intracellular signaling pathways regulated by this CAM. N-cadherin antagonists and agonists are then described, and several potential therapeutic applications of these intercellular adhesion modulators are considered. The usefulness of N-cadherin antagonists in treating fibrotic diseases and cancer, as well as manipulating vascular function are emphasized. Biomaterials incorporating N-cadherin modulators for tissue regeneration are also presented. N-cadherin antagonists and agonists have potential for broad utility in the treatment of numerous maladies.

Chicken lens development: complete signature of expression of galectins during embryogenesis and evidence for their complex formation with α-, β-, δ-, and τ-crystallins, N-CAM, and N-cadherin obtained by affinity chromatography

The emerging multifunctionality of galectins by specific protein-glycan/protein interactions explains the interest to determine their expression during embryogenesis. Complete network analysis of all seven chicken galectins (CGs) is presented in the course of differentiation of eye lens that originates from a single type of progenitor cell. It answers the questions on levels of expression and individual patterns of distribution. A qualitative difference occurs in the CG-1A/B paralogue pair, underscoring conspicuous divergence. Considering different cell phenotypes, lens fiber and also epithelial cells can both express the same CG, with developmental upregulation for CG-3 and CG-8. Except for expression of the lens-specific CG (C-GRIFIN), no other CG appeared to be controlled by the transcription factors L-Maf and Pax6. Studying presence and nature of binding partners for CGs, we tested labeled galectins in histochemistry and in ligand blotting. Mass spectrometric (glyco)protein identification after affinity chromatography prominently yielded four types of crystallins, N-CAM, and, in the cases of CG-3 and CG-8, N-cadherin. Should such pairing be functional in situ, it may be involved in tightly packing intracellular lens proteins and forming membrane contact as well as in gaining plasticity and stability of adhesion processes. The expression of CGs throughout embryogenesis is postulated to give meaning to spatiotemporal alterations in the local glycome.

Integration of Cadherin Adhesion and Cytoskeleton at Adherens Junctions

The cadherin-catenin adhesion complex is the key component of the intercellular adherens junction (AJ) that contributes both to tissue stability and dynamic cell movements in epithelial and nonepithelial tissues. The cadherin adhesion complex bridges neighboring cells and the actin-myosin cytoskeleton, and thereby contributes to mechanical coupling between cells which drives many morphogenetic events and tissue repair. Mechanotransduction at cadherin adhesions enables cells to sense, signal, and respond to physical changes in their environment. Central to this process is the dynamic link of the complex to actin filaments (F-actin), themselves structurally dynamic and subject to tension generated by myosin II motors. We discuss in this review recent breakthroughs in understanding molecular and cellular aspects of the organization of the core cadherin-catenin complex in adherens junctions, its association to F-actin, its mechanosensitive regulation, and dynamics.

Synaptopodin couples epithelial contractility to α-actinin-4-dependent junction maturation

A novel tension-sensitive junctional protein, synaptopodin, can relay biophysical input from cellular actomyosin contractility to induce biochemical changes at cell–cell contacts, resulting in structural reorganization of the junctional complex and epithelial barrier maturation.

The epithelial junction experiences mechanical force exerted by endogenous actomyosin activities and from interactions with neighboring cells. We hypothesize that tension generated at cell–cell adhesive contacts contributes to the maturation and assembly of the junctional complex. To test our hypothesis, we used a hydraulic apparatus that can apply mechanical force to intercellular junction in a confluent monolayer of cells. We found that mechanical force induces α-actinin-4 and actin accumulation at the cell junction in a time- and tension-dependent manner during junction development. Intercellular tension also induces α-actinin-4–dependent recruitment of vinculin to the cell junction. In addition, we have identified a tension-sensitive upstream regulator of α-actinin-4 as synaptopodin. Synaptopodin forms a complex containing α-actinin-4 and β-catenin and interacts with myosin II, indicating that it can physically link adhesion molecules to the cellular contractile apparatus. Synaptopodin depletion prevents junctional accumulation of α-actinin-4, vinculin, and actin. Knockdown of synaptopodin and α-actinin-4 decreases the strength of cell–cell adhesion, reduces the monolayer permeability barrier, and compromises cellular contractility. Our findings underscore the complexity of junction development and implicate a control process via tension-induced sequential incorporation of junctional components.

N-cadherin antagonists as oncology therapeutics

The cell adhesion molecule (CAM), N-cadherin, has emerged as an important oncology therapeutic target. N-cadherin is a transmembrane glycoprotein mediating the formation and structural integrity of blood vessels. Its expression has also been documented in numerous types of poorly differentiated tumours. This CAM is involved in regulating the proliferation, survival, invasiveness and metastasis of cancer cells. Disruption of N-cadherin homophilic intercellular interactions using peptide or small molecule antagonists is a promising novel strategy for anti-cancer therapies. This review discusses: the discovery of N-cadherin, the mechanism by which N-cadherin promotes cell adhesion, the role of N-cadherin in blood vessel formation and maintenance, participation of N-cadherin in cancer progression, the different types of N-cadherin antagonists and the use of N-cadherin antagonists as anti-cancer drugs.

Breakdown of interlocking domains may contribute to formation of membranous globules and lens opacity in ephrin-A5(-/-) mice

Ephrin-A5, a ligand of the Eph family of receptor tyrosine kinases, plays a key role in lens fiber cell packing and cell-cell adhesion, with approximately 87% of ephrin-A5(-/-) mice develop nuclear cataracts. Here, we investigated the extensive formation of light-scattering globules associated with breakdown of interlocking protrusions during lens opacification in ephrin-A5(-/-) mice. Lenses from wild-type (WT) and ephrin-A5(-/-) mice between 2 and 21 weeks old were studied with light and electron microscopy, immunofluorescence labeling, freeze-fracture TEM and filipin cytochemistry for membrane cholesterol detection. Lens opacities with various densities were first observed in ephrin-A5(-/-) mice at around 60 days old. Dense cataracts in the mutant lenses were seen primarily in the nuclear region surrounded by transparent cortices from all eyes examined. We confirmed that a majority of nuclear cataracts were dislocated posteriorly and ruptured the thinner posterior lens capsule. SEM analysis indicated that numerous interlocking protrusions and wavy ridge-and-valley membrane surfaces in deep cortical and nuclear fibers did not cause lens opacity in both transparent ephrin-A5(-/-) and WT mice. In contrast, abundant isolated membranous globules of approximately 1000 nm in size were distributed randomly along the intact fiber cells during early stage of all ephrin-A5(-/-) cataracts examined. A further examination using both SEM and TEM revealed that isolated globules were generated from the disintegrated interlocking protrusions originally located along the corners of hexagonal fiber cells. Freeze-fracture TEM further revealed the association of square-array aquaporin junctions with both isolated globules and interlocking membrane domains. This study reports for the first time that disrupted interlocking protrusions are the source of numerous large membranous globules that contribute to light scattering and nuclear cataracts in the ephrin-A5(-/-) mice. Our results further suggest that dissociations of N-cadherin and adherens junctions in the associated interlocking domains may result in the formation of isolated globules and nuclear opacities in the ephrin-A5(-/-) mice.

N-Cadherin is a prospective cell surface marker of human mesenchymal stem cells that have high ability for cardiomyocyte differentiation

Mesenchymal stem cells (MSCs) are among the most promising sources of stem cells for regenerative medicine. However, the range of their differentiation ability is very limited. In this study, we explored prospective cell surface markers of human MSCs that readily differentiate into cardiomyocytes. When the cardiomyogenic differentiation potential and the expression of cell surface markers involved in heart development were analyzed using various immortalized human MSC lines, the MSCs with high expression of N-cadherin showed a higher probability of differentiation into beating cardiomyocytes. The differentiated cardiomyocytes expressed terminally differentiated cardiomyocyte-specific markers such as α-actinin, cardiac troponin T, and connexin-43. A similar correlation was observed with primary human MSCs derived from bone marrow and adipose tissue. Moreover, N-cadherin-positive MSCs isolated with N-cadherin antibody-conjugated magnetic beads showed an apparently higher ability to differentiate into cardiomyocytes than the N-cadherin-negative population. Quantitative polymerase chain reaction analyses demonstrated that the N-cadherin-positive population expressed significantly elevated levels of cardiomyogenic progenitor-specific transcription factors, including Nkx2.5, Hand1, and GATA4 mRNAs. Our results suggest that N-cadherin is a novel prospective cell surface marker of human MSCs that show a better ability for cardiomyocyte differentiation.

Cell adhesion molecule expression in human lens epithelial cells after corticosteroid exposure

Aim:

The aim of the study was to investigate changes in cell adhesion molecule expression in human lens epithelial cells (HLEC) subjected to glucocorticoids.

Methods:

Human lens epithelial cells were exposed to different concentrations of dexamethasone for 24 hours. Cell adhesion molecule expression was studied by western blot and immunohistochemistry of vimentin, N-cadherin, E-cadherin, α-catenin, β-catenin and γ-catenin. Expression of the glucocorticoid receptor (GR) was also studied. Cell morphology was examined by transmission electron microscopy (TEM).

Result:

Expression of N-cadherin, α-catenin, β-catenin and GR was significantly decreased in dexamethasone exposed cells as compared to unexposed cells. No significant change in γ-catenin was present. Visualization of adhesion molecules, N-cadherin and α-catenin, by immunohistochemistry showed decreased antigen reactivity in dexamethasone exposed as compared to the unexposed cells. However, no change was seen for β-catenin and γ-catenin. E-cadherin was not detectable using western blot or immunohistochemistry.

TEM showed multilayering of cells, vacuole formation and appearance of electron-dense multivesicular bodies in HLEC exposed to 0, 0.1, 1, 10 and 100 αM dexamethasone.

Conclusion:

Glucocorticoids affect several adhesion molecules in lens epithelial cells, something that may contribute to the pathogenesis of posterior subcapsular opacification.

Cell-cell junctional proteins in cardiovascular mechanotransduction

Cell-cell junctional proteins play important structural and functional roles in several physiological systems. Recent studies have illuminated key aspects in the relationship of junctional proteins with normal cell and tissue function as well as various pathologies. In this review article, the roles of cell-cell junctional proteins will be presented in four classes: adherens junctions, desmosomes, gap junctions, and tight junctions, and discussed primarily in the context of cardiovascular cell and tissue physiology and pathophysiology. The functions of the proteins are described from the perspective of mechanotransductive regulation of physiological and disease processes, with focus being laid on more biomechanical aspects, such as cell adhesion, migration, and mechanosignaling.

Ultrastructural changes in cardiac myocytes from Boxer dogs with arrhythmogenic right ventricular cardiomyopathy

OBJECTIVES

We sought to quantify the number and length of desmosomes, gap junctions, and adherens junctions in arrhythmogenic right ventricular cardiomyopathy (ARVC) and non-ARVC dogs, and to determine if ultrastructural changes existed.

ANIMALS

Hearts from 8 Boxer dogs afflicted with histopathologically confirmed ARVC and 6 dogs without ARVC were studied.

METHODS

Quantitative transmission electron microscopy (TEM) and Western blot semi-quantification of α-actinin were used to study the intercalated disc and sarcomere of the right and left ventricles.

RESULTS

When ARVC dogs were compared to non-ARVC dogs reductions in the number of desmosomes (P = 0.04), adherens junctions (P = 0.04) and gap junctions (P = 0.02) were found. The number of gap junctions (P = 0.04) and adherens junctions (P = 0.04) also were reduced in the left ventricle, while the number of desmosomes was not (P = 0.88). A decrease in the length of desmosomal complexes within LV samples (P = 0.04) was found. These findings suggested disruption of proteins providing attachment of the cytoskeleton to the intercalated disc. Immunoblotting did not demonstrate a quantitative reduction in the amount of α-actinin in ARVC afflicted samples. All Boxers with ARVC demonstrated the presence of electron dense material originating from the Z band and extending into the sarcomere, apparently at the expense of the cytoskeletal structure.

CONCLUSIONS

These results emphasize the importance of structural integrity of the intercalated disc in the pathogenesis of ARVC. In addition, observed abnormalities in sarcomeric structure suggest a novel link between ARVC and the actin-myosin contractile apparatus.

N-cadherin cell-cell adhesion complexes are regulated by fibronectin matrix assembly

Fibronectin is a principal component of the extracellular matrix. Soluble fibronectin molecules are assembled into the extracellular matrix as insoluble, fibrillar strands via a cell-dependent process. In turn, the interaction of cells with the extracellular matrix form of fibronectin stimulates cell functions critical for tissue repair. Cross-talk between cell-cell and cell-extracellular matrix adhesion complexes is essential for the organization of cells into complex, functional tissue during embryonic development and tissue remodeling. Here, we demonstrate that fibronectin matrix assembly affects the organization, composition, and function of N-cadherin-based adherens junctions. Using fibronectin-null mouse embryonic myofibroblasts, we identified a novel quaternary complex composed of N-cadherin, β-catenin, tensin, and actin that exists in the absence of a fibronectin matrix. In the absence of fibronectin, homophilic N-cadherin ligation recruited both tensin and α5β1 integrins into nascent cell-cell adhesions. Initiation of fibronectin matrix assembly disrupted the association of tensin and actin with N-cadherin, released α5β1 integrins and tensin from cell-cell contacts, stimulated N-cadherin reorganization into thin cellular protrusions, and decreased N-cadherin adhesion. Fibronectin matrix assembly has been shown to recruit α5β1 integrins and tensin into fibrillar adhesions. Taken together, these studies suggest that tensin serves as a common cytoskeletal link for integrin- and cadherin-based adhesions and that the translocation of α5β1 integrins from cell-cell contacts into fibrillar adhesions during fibronectin matrix assembly is a novel mechanism by which cell-cell and cell-matrix adhesions are coordinated.

Post-operative capsular opacification: a review

Post-operative capsular opacification is a multifactorial physiological consequence of cataract surgery. Opacification involving the central posterior capsule has a significant impact on high and low contrast acuity and low contrast sensitivity. The assessment of Posterior Capsule Opacification (PCO) on cadaver eyes, experimental studies, culture models and in clinical studies has provided an understanding of its pathogenesis. The proliferation, migration and abnormal differentiation of residual lens epithelial cells and fibers in the capsular bag have been implicated in the pathogenesis of PCO. The incidence and severity of PCO correlates to the meticulous use of surgical techniques, IOL optic edge designs and IOL materials. This article summarizes the clinical studies with recommendations for retarding the development of central PCO. It discusses experiments with pharmacological agents broadly categorized as anti-inflammatory, immuno-modulating, antiproliferative, antiadhering, antitransdifferentiating agents for the prevention of PCO. These studies will remain critical for future endeavors undertaken for eradication of PCO.

Ultrastructural analysis of development of myocardium in calreticulin-deficient mice

BACKGROUND

Calreticulin is a Ca2+ binding chaperone of the endoplasmic reticulum which influences gene expression and cell adhesion. The levels of both vinculin and N-cadherin are induced by calreticulin expression, which play important roles in cell adhesiveness. Cardiac development is strictly dependent upon the ability of cells to adhere to their substratum and to communicate with their neighbours.

RESULTS

We show here that the levels of N-cadherin are downregulated in calreticulin-deficient mouse embryonic hearts, which may lead to the disarray and wavy appearance of myofibrils in these mice, which we detected at all investigated stages of cardiac development. Calreticulin wild type mice exhibited straight, thick and abundant myofibrils, which were in stark contrast to the thin, less numerous, disorganized myofibrils of the calreticulin-deficient hearts. Interestingly, these major differences were only detected in the developing ventricles while the atria of both calreticulin phenotypes were similar in appearance at all developmental stages. Glycogen also accumulated in the ventricles of calreticulin-deficient mice, indicating an abnormality in cardiomyocyte metabolism.

CONCLUSION

Calreticulin is temporarily expressed during heart development where it is required for proper myofibrillogenesis. We postulate that calreticulin be considered as a novel cardiac fetal gene.

The role of the lens actin cytoskeleton in fiber cell elongation and differentiation

The vertebrate ocular lens is a fascinating and unique transparent tissue that grows continuously throughout life. During the process of differentiation into fiber cells, lens epithelial cells undergo dramatic morphological changes, membrane remodeling, polarization, transcriptional activation and elimination of cellular organelles including nuclei, concomitant with migration towards the lens interior. Most of these events are presumed to be influenced in large part, by dynamic reorganization of the cellular actin cytoskeleton and by intercellular and cell: extracellular matrix interactions. In light of recent and unprecedented advancement in our understanding of the mechanistic bases underlying regulation of actin cytoskeletal dynamics and the role of the actin cytoskeleton in cell function, this review attempts to summarize current knowledge regarding the role of the cellular actin cytoskeleton, in lens fiber cell elongation and differentiation, and regulation of actin cytoskeletal organization in the lens.

Differential effects of N-cadherin-mediated adhesion on the development of myotomal waves

Myotomal fibers form by a first wave of pioneer myoblasts from the medial epithelial somite, and by a second wave from all four lips of the dermomyotome. Then, a third wave of mitotic progenitors colonizes the myotome,initially stemming from the extreme lips and, later, from the central dermomyotome sheet. In vitro studies have suggested that N-cadherin plays a role in myogenesis, but its role in vivo remains poorly understood. We find that during the growth phase of the dermomyotome sheet, when the orientation of mitotic spindles is parallel to the mediolateral extent of the epithelium,N-cadherin protein is inherited by both daughter cells. Prior to dermomyotome dissociation into dermis and muscle progenitors, when mitoses become perpendicularly oriented, N-cadherin remains associated only with the apical cell located in apposition to the myotome, generating molecular asymmetry between basal and apical progeny. Local gene missexpression confirms that N-cadherin-mediated adhesion is sufficient to promote myotome colonization,whereas its absence drives cells towards the subectodermal domain, hence coupling the asymmetric distribution of N-cadherin to a shift in mitotic orientation and to fate segregation. Site-directed electroporation to additional, discrete somite regions, further reveals that N-cadherin-mediated adhesion is necessary for maintaining the epithelial configuration of all dermomyotome domains while promoting the onset of Myod transcription and the translocation into the myotome of myofibers and/or of Pax-positive progenitors. By contrast, N-cadherin has no effect on migration or differentiation of the first wave of myotomal pioneers. Altogether, we show for the first time that the asymmetric localization of N-cadherin during mitosis indirectly influences fate segregation by differentially driving the allocation of progenitors to muscle versus dermal primordia, that the adhesive domain of N-cadherin maintains the integrity of the dermomyotome epithelium,which is necessary for myogenic specification, and that different molecular mechanisms underlie the establishment of pioneer and later myotomal waves.

The transitional junction: a new functional subcellular domain at the intercalated disc

We define here a previously unrecognized structural element close to the heart muscle plasma membrane at the intercalated disc where the myofibrils lead into the adherens junction. At this location, the plasma membrane is extensively folded. Immunofluorescence and immunogold electron microscopy reveal a spectrin-rich domain at the apex of the folds. These domains occur at the axial level of what would be the final Z-disc of the terminal sarcomere in the myofibril, although there is no Z-disc-like structure there. However, a sharp transitional boundary lies between the myofibrillar I-band and intercalated disc thin filaments, identifiable by the presence of Z-disc proteins, alpha-actinin, and N-terminal titin. This allows for the usual elastic positioning of the A-band in the final sarcomere, whereas the transduction of the contractile force normally associated with the Z-disc is transferred to the adherens junctions at the plasma membrane. The axial conjunction of the transitional junction with the spectrin-rich domains suggests a mechanism for direct communication between intercalated disc and contractile apparatus. In particular, it provides a means for sarcomeres to be added to the ends of the cells during growth. This is of particular relevance to understanding myocyte elongation in dilated cardiomyopathy.

The area composita of adhering junctions connecting heart muscle cells of vertebrates. I. Molecular definition in intercalated disks of cardiomyocytes by immunoelectron microscopy of desmosomal proteins

Among sarcomeric muscles the cardiac muscle cells are unique by, inter alia, a systemic and extended cell-cell contact structure, the intercalated disk (ID), comprising frequent and closely spaced arrays of plaque-coated cell-cell adhering junctions (AJs). As some of these junctions may look somewhat like desmosomes and others like fasciae adhaerentes, the dogma has emerged in the literature that IDs contain - like epithelial cells - both kinds of AJs formed by - for the most - mutually exclusive molecular ensembles. This, however, is not the case. In comprehensive immunoelectron microscopic studies of mammalian (human, bovine, rat, mouse) and non-mammalian (chicken, amphibia, fishes) heart muscle tissues, we have localized major constituents of the desmosomal plaques of polar epithelia, desmoplakin, plakophilin-2 and plakoglobin, as well as the desmosomal cadherins, desmoglein Dsg2 and desmocollin Dsc2, in both kinds of ID AJs, independent of the specific morphological appearance. The desmosomal molecules are not restricted to the desmosome-like-looking junctions but can also be detected in junctions appearing similar to the zonula or fascia adhaerens structures. These AJs of cardiac ID are therefore subsumed under the collective term area composita. We discuss our results with respect to the importance of ID junction molecules for the formation, maintenance and function of the heart, particularly in relation to recent findings that deletions of - or mutations in - genes encoding such proteins can cause severe, sometimes lethal damages.

N-Cadherin: structure, function and importance in the formation of new intercalated disc-like cell contacts in cardiomyocytes

N-Cadherin belongs to a superfamily of calcium-dependent transmembrane adhesion proteins. It mediates adhesion in the intercalated discs at the termini of cardiomyocytes thereby serving as anchor for myofibrils at cell-cell contacts. A large body of data on the molecular structure and function of N-cadherin exists, however, little is known concerning spatial and temporal interactions between the different junctional structures during formation of the intercalated disc and its maturation in postnatal development. The progression of compensated left ventricular hypertrophy to congestive left heart failure is accompanied by intercalated disc remodeling and has been demonstrated in animal models and in patients. The long-term culture of adult rat cardiomyocytes allows to investigate the development of de novo intercalated disc-like structures. In order to analyze the dynamics of the cytoskeletal redifferentiation in living cells, we used the expression of chimeric proteins tagged with the green fluorescent protein reporter. This technique is becoming a routine method in basic research and complements video time-lapse and confocal microscopy. Cultured cardiomyocytes have been used for a variety of studies in cell biology and pharmacology. Their ability to form an electrically coupled beating tissue-like network in culture possibly allows reimplantation of such cells into injured myocardium, where they eventually will form new contacts with the healthy muscle tissue. Several groups have already shown that cardiomyocytes can be grafted successfully into sites of myocardial infarcts or cryoinjuries. Autologous adult cardiomyocyte implantation, might indeed contribute to cardiac repair after infarction, thanks to advances in tissue engineering.

N-cadherin-mediated cell adhesion determines the plasticity for cell alignment in response to mechanical stretch in cultured cardiomyocytes

Mechanical stretch has been implicated as the growth stimuli in the heart. Physiologically, mechanical stretch is reported to contribute to the orientation of cardiomyocytes, though the molecular mechanism remains to be elucidated. This study was designed to make clear functional significances of N-cadherin in plasticity of cell alignment in response to mechanical stretch. Neonatal rat cardiomyocytes, cultured on silicone dishes, were subjected to artificial uniaxial cyclic stretch. Mechanical stretch was started at certain times (3-75h) after seeding and continued for 24h. Stretch stimulation in 3h after cultivation promoted cell orientation running parallel to tension direction. In contrast, cardiac myocytes fail to align when exposed to stretch 24-75h after cultivation. To address the importance of N-cadherin in the responsiveness to stretch, the expression and distribution of N-cadherin were analyzed. Immediately after seeding, N-cadherin showed dispersed distributions. During cultivation, N-cadherin localized to cell-cell contacts accompanied by the upregulation of its protein. Next, to investigate influence of cell-cell adhesion, cardiomyocytes cultured for 72h were replated by trypsin treatment and exposed to stretch 3h after replating. The cardiomyocytes replated by trypsinization were oriented in parallel to tension direction by mechanical stretch. Finally, adenoviral transfection of dominant-negative N-cadherin recovered the ability to exhibit cell orientation in response to stretch. Our results suggested that N-cadherin was involved in the oriented responses of cardiomyocytes induced by mechanical stretch.

Endogenous N-cadherin in a subpopulation of MDCK cells: distribution and catenin complex composition

Epithelial (E)-cadherin plays a critical role in developing a normal epithelial phenotype but neural (N)-cadherin can disrupt epithelial shape, at least in carcinoma-derived cells. Here the normal epithelial cell line MDCK was used to select for a trypsin-sensitive (TS-MDCK) subpopulation that expresses low levels of endogenous N-cadherin. Similar amounts of E-cadherin and all catenins are found in both TS-MDCK and trypsin-resistant cells (TR-MDCK), but TS-MDCK are less phenotypically epithelioid and more motile, and junctional proteins are more detergent soluble. In TS-MDCK, N-cadherin is largely nonjunctional; a similar N-cadherin distribution and mesenchymal phenotype are found in TR-MDCK transfected to express low levels of exogenous N-cadherin. Little N-cadherin was attracted to junctions between TS-MDCK and hTERT-RPE1 cells, a retinal pigment epithelium-derived line that expresses dominantly N-cadherin. No differences were seen in E-cadherin-catenin complexes in TS- and TR-MDCK, but N-cadherin-catenin complexes in TS-MDCK have more abundant p120 catenin. Overall, the results indicate that E- and N-cadherin assemble stoichiometrically different complexes with p120 in the same cells. Further, N-cadherin does not participate with E-cadherin in a zonular epithelial junction in normal MDCK epithelial cells. Rather, even low levels of endogenous N-cadherin contribute to a disrupted epithelial phenotype, resembling the effect of N-cadherin on carcinoma-derived epithelial cells.

Signals through gp130 upregulate Wnt5a and contribute to cell adhesion in cardiac myocytes

Glycoprotein 130 (gp130), a common receptor of IL-6 family cytokines, plays critical roles in cardiac functions. Here, we demonstrate that the stimulation of gp130 with leukemia inhibitory factor (LIF) promoted cell adhesion in a cadherin-dependent manner in cultured cardiomyocytes. Wnt5a was upregulated by the stimulation of gp130 with IL-6 family cytokines, accompanied by N-cadherin protein upregulation. Wnt5a was not induced by LIF in cardiomyocytes expressing dominant-negative STAT3. Ablation of Wnt5a by antisense cDNA inhibited LIF-induced cell adhesion. Collectively, signals through gp130 upregulate Wnt5a through STAT3, promoting the N-cadherin-mediated cell adhesion.

Role of catenins in the development of gap junctions in rat cardiomyocytes

Gap junctions are intercellular communicating channels responsible for the synchronized activity of cardiomyocytes. Recent studies have shown that the membrane-associated guanylate kinase protein, zonula occludens-1 (ZO-1) can bind to catenins in epithelial cells and act as an adapter for the transport of the connexin isotype, Cx43 during gap junction formation. The significance of catenins in the development of gap junctions and whether complexes between catenins and ZO-1 are formed in cardiomyocytes are not clear. In this study, immunofluorescence and confocal microscopy showed sequential redistribution of alpha-catenin, beta-catenin, ZO-1, and Cx43 to the plasma membrane when rat cardiomyocytes were cultured in low Ca(2+) (<5 microM) medium, then shifted to 1.8 mM Ca(2+) medium (Ca(2+) switch). Diffuse cytoplasmic staining of alpha-catenin, beta-catenin, ZO-1, and Cx43 was seen in the cytoplasm when cardiomyocytes were cultured in low Ca(2+) medium. Staining of alpha-catenin, beta-catenin, and ZO-1 was detected at the plasma membrane of cell-cell contact sites 10 min after Ca(2+) switch, whereas Cx43 staining was first detected, colocalized with ZO-1 at the plasma membrane, 30 min after Ca(2+) switch. Distinct junctional and extensive cytoplasmic staining of alpha-catenin, beta-catenin, ZO-1, and Cx43 was seen 2 h after Ca(2+) switch. Immunoprecipitation of Triton X-100 cardiomyocyte extracts using anti-beta-catenin antibodies showed that beta-catenin was associated with alpha-catenin, ZO-1, and Cx43 at 2 h after Ca(2+) switch. Intracellular application of antisera against alpha-catenin, beta-catenin, or ZO-1 by electroporation of cardiomyocytes cultured in low Ca(2+) medium inhibited the redistribution of Cx43 to the plasma membrane following Ca(2+) switch. These results suggest the formation of a catenin-ZO-1-Cx43 complex in rat cardiomyocytes and that binding of catenins to ZO-1 is required for Cx43 transport to the plasma membrane during the assembly of gap junctions.

N-cadherin mediates axon-aligned process growth and cell-cell interaction in rat Schwann cells

The molecular mechanisms underlying the contact behavior of Schwann cells (SCs) and SC-axon association are poorly understood. SC-SC and SC-axon interactions were studied using purified adult rat SCs and cocultures of SCs with embryonic dorsal root ganglion neurons. After contact of SCs with axons, SCs start to extend processes in alignment with axons. This unique alignment was quantitated using a new assay. SC-axon alignment and SC-SC band formation were disrupted in medium containing low extracellular calcium, indicating the involvement of calcium-dependent adhesion molecules. N-cadherin expression was strong in developing rat sciatic nerves but weak in adult sciatic nerves. In purified adult-derived rat SCs, N-cadherin expression was increased by mitogens (neuregulins) and decreased by high cell density. High-resolution confocal images show intense N-cadherin signals in SC process tips. Subcellular N-cadherin was accumulated in bands at intercellular junctions between SCs and was clustered at axon-SC contact sites. Blocking antibodies (rabbit and guinea pig IgG directed against the first extracellular domain of N-cadherin) and cyclic pentapeptides (including the HAV motif) were used to perturb N-cadherin function. All blocking agents reduced the number of N-cadherin-positive SC-SC junctions and perturbed axon-aligned growth of SC processes. Averaging over all N-cadherin-perturbation experiments, in controls 67-86% of SCs exhibited axon-aligned process growth, whereas in treated cultures only 41% of the SCs aligned with axons. These results are evidence that in mammals N-cadherin is important for formation of SC-SC junctions and SC process growth in alignment with axons.

Role of N-cadherin- and integrin-based costameres in the development of rat cardiomyocytes

Costameres, vinculin-containing structures found in skeletal and cardiac muscle, are thought to anchor the Z-discs of the peripheral myofibrils to the sarcolemma. Several lines of evidence indicate that two different sets of costameres, integrin- and N-cadherin-based, are present in cardiac muscles. In this study, immunoblot analysis was used to study the expression of N-cadherin, alpha-catenin, beta-catenin, vinculin, talin, and laminin in rat cardiac muscles at embryonic days 15 and 19, the day of birth (postnatal day 0), postnatal weeks 1, 2, 3, and 4, and in the adult. Double immunofluorescence microscopy was performed to study the spatial and temporal distribution of these two sets of costameres in rat cardiomyocytes. Costameric staining for N-cadherin, codistributed with beta-catenin, was strong from embryonic day 15 up to postnatal week 2, gradually decreased after postnatal week 3, and was undetectable at postnatal week 4 and in the adult. Confocal microscopy showed that N-cadherin colocalized with alpha-actinin at cortical myofibrils. Double-labeling of beta-catenin and talin indicated the coexistence of N-cadherin/catenin- and integrin/talin-based costameres in rat cardiac muscle. Although beta-catenin and vinculin were co-localized at the costamere of cardiomyocytes from embryonic day 15 to postnatal week 3, staining for beta-catenin or talin was mutually exclusive at all stages examined. These results demonstrate the simultaneous, but mutually exclusive, existence of N-cadherin/catenin- and integrin/talin-based costameres in rat cardiomyocytes between late embryonic stages and postnatal week 3, while only integrin/talin-based costameres were found in adult rats. The N-cadherin/catenin-based costameres in rat cardiac muscles may play a role in myofibrillogenesis similar to that of their counterparts in cultured cardiomyocytes.

Spatiotemporal distribution of zonulae adherens and associated actin bundles in both epithelium and fiber cells during chicken lens development

Zonulae adherens and associated actin bundles (ZA/AB) are believed to play a major role in epithelial folding and invagination during morphogenesis of neural tube and other vesicular structures. The lens morphogenesis is associated with the formation of the lens vesicle in which ZA/AB would be needed during the formation process. However, the existence of ZA/AB in the lens has never been established. In this study we report for the first time the existence of ZA/AB in both lens epithelium and fiber cells during embryonic development of chicken lens from E4 to E20. Light microscopy revealed contacts between the lens epithelium and primary fiber cells, and between the lens epithelium and secondary fiber cells at E4 and E11, respectively. Thin-section electron microscopy consistently revealed ZA/AB near both the apical ends of lens epithelial cells and primary fiber cells at E4. This arrangement manifests as a parallel pair of belt-like ZA/AB along the epithelium-fiber interface. In semi-tangential sections, a continuous belt-like ZA/AB was also evidenced in individual epithelial cells and fiber cells. Furthermore, the same ZA/AB arrangement was observed near both the apical ends of epithelial cells and secondary fiber cells at E11. Besides ZA/AB, macular-type fasciae adherens were distributed regularly between epithelial cells, between primary fibers, between secondary fibers, and between epithelium and both primary and secondary fibers. Immunofluorescence strongly and preferentially labeled N-cadherin at both the apical ends of lens epithelium and primary or secondary fibers at the corresponding ages, suggesting a direct association with the zonulae adherens. Also punctate N-cadherin labeling was commonly seen along various regions of primary and secondary fiber cells at different ages, and to a larger extent in the mature fibers of older lenses. This study suggests that: (1) ZA/AB located at the apices of lens epithelial cells may play a crucial role in the early stages of lens morphogenesis (e.g. lens vesicle formation); (2) ZA/AB of primary and secondary fiber cells originate from the epithelial cells during their elongation and differentiation; (3) owing to the restricted distribution of ZA/AB, abundant fasciae adherens are needed to maintain the structural stability of the epithelium and fiber cells during development and maturation; and (4) N-cadherin is the principle adhesion protein for both the zonulae adherens and fasciae adherens in the lens.

Immobilized dimers of N-cadherin-Fc chimera mimic cadherin-mediated cell contact formation: contribution of both outside-in and inside-out signals

Cell adhesion receptors of the cadherin family are involved in various developmental processes, affecting cell adhesion and migration, and also cell proliferation and differentiation. In order to dissect the molecular mechanisms of cadherin-based cell-cell adhesion and subsequent signal transduction to the cytoskeleton and/or cytoplasm leading to adapted cell responses, we developed an approach allowing us to mimic and control cadherin activation. We produced a dimeric N-cadherin-Fc chimera (Ncad-Fc) which retains structural and functional properties of cadherins, including glycosylation, Ca(2+)-dependent trypsin sensitivity and the ability to mediate Ca(2+)-dependent self-aggregation of covered microbeads. Beads covered with either Ncad-Fc or anti-N-cadherin antibodies specifically bound to N-cadherin expressing cells. Both types of beads induced the recruitment of N-cadherin, beta-catenin, alpha-catenin and p120, by lateral mobilization of preexisting cell membrane complexes. Furthermore, cadherin clustering elicited by Ncad-Fc beads triggered local accumulations of tyrosine phosphorylated proteins, a recruitment and redistribution of actin filaments, as well as local membrane remodeling. These results support a model where the adhesion of cadherin ectodomains is followed by clustering of cadherin/catenin complexes allowing signal transduction affecting both cytoskeletal reorganization and cytoplasmic signal mobilization (outside-in signaling). Interestingly, bead-cell binding was altered by agents promoting microfilament and microtubule depolymerization or tyrosine phosphorylation, indicating a possible regulation of the adhesive properties of the extracellular domain of N-cadherin by intracellular factors (inside-out signaling).

N-cadherin function is required for differentiation-dependent cytoskeletal reorganization in lens cells in vitro

Members of the cadherin family of cell adhesion molecules participate in calcium-dependent cell-cell adhesions that are necessary for the cell sorting events that regulate early developmental processes. Although individual cadherin molecules have been shown to participate in tissue histogenesis, the regulation of function of these receptors in cell differentiation has been more difficult to identify. We have determined that N-cadherin linkage to the cytoskeleton is correlated with lens cell differentiation in vivo. Through the use of a chick embryo lens culture system that mimics differentiation in vivo, we have determined that N-cadherin linkage to the cytoskeleton is altered and lens differentiation is blocked by function-blocking antibodies to N-cadherin. In the presence of the N-cadherin function-blocking antibody, NCD-2, both N-cadherin and filamentous actin are prevented from organizing at the cortical membranes. This correlates with an inhibition of lens morphogenesis and differentiation. These results are paralleled by changes in the expression of the molecular components of the cadherin-catenin complex and their linkage to the actin cytoskeleton. In the presence of NCD-2, expression of N-cadherin, alpha-catenin, and beta-catenin is inhibited and their association with the cytoskeleton blocked. Overall cadherin expression, however, remains unchanged as demonstrated by studies with a pan-cadherin antibody. This is accompanied by an increase in expression of the cadherin cytoskeletal protein plakoglobin. Although the cells have tried to compensate for the loss of N-cadherin by up-regulation of another cadherin(s) and plakoglobin, this is unable to compensate for N-cadherin function. The data strongly suggest that N-cadherin and its associated cytoskeleton play an important role in the differentiation process that leads to the formation of the crystalline lens.

Presenilin-1 forms complexes with the cadherin/catenin cell-cell adhesion system and is recruited to intercellular and synaptic contacts

In MDCK cells, presenilin-1 (PS1) accumulates at intercellular contacts where it colocalizes with components of the cadherin-based adherens junctions. PS1 fragments form complexes with E-cadherin, beta-catenin, and alpha-catenin, all components of adherens junctions. In confluent MDCK cells, PS1 forms complexes with cell surface E-cadherin; disruption of Ca(2+)-dependent cell-cell contacts reduces surface PS1 and the levels of PS1-E-cadherin complexes. PS1 overexpression in human kidney cells enhances cell-cell adhesion. Together, these data show that PS1 incorporates into the cadherin/catenin adhesion system and regulates cell-cell adhesion. PS1 concentrates at intercellular contacts in epithelial tissue; in brain, it forms complexes with both E- and N-cadherin and concentrates at synaptic adhesions. That PS1 is a constituent of the cadherin/catenin complex makes that complex a potential target for PS1 FAD mutations.

Cell adhesion and the actin cytoskeleton of the enveloping layer in the zebrafish embryo during epiboly

As the zebrafish embryo undergoes gastrulation and epiboly, the cells of the enveloping layer (EVL) expand, covering the entire yolk cell. During the epiboly process, the EVL cells move as a coherent layer, remaining tightly attached to each other and to the underlying yolk syncytial layer (YSL). In view of the central role of the actin cytoskeleton, in both cell motility and cell cell adhesion, we have labeled these cells in situ with fluorescent phalloidin and anti-actin antibodies. We show that, throughout their migration, the EVL cells retain a conspicuous cortical actin cytoskeletal belt coinciding with cell surface cadherins. At the margins approaching the YSL, the EVL cells extend, from their apicolateral domains, actin-rich filopodial protrusions devoid of detectable cadherin. We have studied the role of the actin cytoskeleton in the maintenance of EVL cohesion during epiboly. Cytochalasin treatment of embryos induces EVL dissociation accompanied by general detachment of the rest of the embryonic cells. In the dissociating EVL cells, the cortical actin belt undergoes fragmentation with the formation of actin aggregates; cadherins, on the other hand, remain evenly distributed at the junctional cell surface. Removal of Ca2+ by ethyleneglycolbis (amino-ethyl-ether)-tetraacetic acid (EGTA) treatment also induces cell dissociation without visible disruption of the cortical actin belt. The protein kinase inhibitor (1-isoquinolinylsulfonyl)-2-methyl-piperazine dihydrochloride (H-7), which blocks acto-myosin contractility and disrupts actin cables in cultured cells, also potentiates cytochalasin-induced dissociation and promotes the projection of numerous actin-rich lamellipodial extensions. The fact that EVL cells produce microspike-like structures towards the YSL and are capable of lamellipodial activity lend further support to the suggestion (R.W. Keller and J.P. Trinkaus. 1987. Dev. Biol. 120: 12-24) that the EVL cells are not passively mobilized on the expanding YSL but actively participate in epiboly.Key words: actin, adhesion, cadherin, cytochalasin, embryo, zebrafish.

TNF-alpha and IL-1beta suppress N-cadherin expression in MC3T3-E1 cells

Excessive production of tumor necrosis factor (TNF) and interleukin-1 (IL-1) secondary to estrogen deficiency have been implicated as the cause of osteoporosis in postmenopausal woman. These cytokines appear to stimulate osteoclast precursor proliferation and activate mature osteoclast formation directly and possibly indirectly via osteoblasts. To investigate the other possible roles that these cytokines may play in stimulating the bone resorption process, we examined the effect of TNF-alpha and IL-1beta on cell-cell adhesion molecules, cadherins, in osteoblastic MC3T3-E1 cells. In this study, we investigated cadherin expression and the effect of TNF-alpha, IL-1beta, and parathyroid hormone (PTH) on the expression of cadherins in MC3T3-E1 cells. Confluent cultures of MC3T3-E1 cells were challenged with recombinant human TNF-alpha (1-100 U/ml), recombinant human IL-1beta (1-100 ng/ml) and human PTH(1-34) (1-100 ng/ml), respectively. The results show that MC3T3-E1 cells express functional cadherin molecules, N-cadherin and OB-cadherin. TNF-alpha (10-100 U/ml) and IL-1beta (10-100 ng/ml) suppressed N-cadherin without changing OB-cadherin expression, while PTH (1-100 ng/ml) had no effect on cadherin expression. These results raise the possibility that TNF-alpha and IL-1beta may compromise the cell-cell adhesion of osteoblasts which cover the bone surface. The ensuing compromised cell-cell adhesion of osteoblasts may in turn facilitate the direct adhesion of osteoclasts on the calcified bone matrix surface. These results implicate an indirect role for osteoblasts in the promotion of bone resorption by TNF-alpha and IL-1beta.

Protein expression of brain endothelial cell E-cadherin after hypoxia/aglycemia: influence of astrocyte contact

The blood-brain barrier (BBB) plays a crucial role in protecting the central nervous system (CNS) from any changes in homeostasis brought about by pathological conditions. Cerebrovascular permeability is an important factor in the development of cerebral edema following stroke [M. Plateel, E. Teissier, R. Cecchelli, Hypoxia, dramatically increases the nonspecific transport of blood-borne proteins to the brain. J. Neurochem. 68 (1997) 874-877] and any changes in its function can have detrimental neurological consequences. Recently, research has shown that an in vitro model of the BBB is sensitive to short exposures of hypoxia/aglycemia and that changes in endothelial cell calcium flux may be responsible for structural and functional variations in the BBB during ischemic stress [T.J. Abbruscato, T.P. Davis, Combination of hypoxia/aglycemia compromises in vitro BBB. J. Pharmacol. Exp. Ther. 289 (1999) 668-675]. Present experiments investigated bovine brain microvessel endothelial cell (BBMEC) expression of a Ca(2+)-dependent cell-cell adhesion molecule, E-cadherin, which has been shown to be important for blood-brain barrier function [D. Pal, K.L. Audus, T.J. Siahaan, Modulation of cellular adhesion in bovine brain microvessel endothelial cells by a decapeptide. Brain Research 747 (1997) 103-113]. Since it is believed that astrocyte-endothelial cell interaction is crucial for maintenance of in vivo BBB characteristics, we have attempted to optimize our isolation and culturing techniques to produce a reliable, in vitro model of the BBB that is suitable to study pathological conditions. Immunofluoresence experiments showed positive staining for E-cadherin, yet failed to show any change in cellular distribution of E-cadherin upon hypoxic/aglycemic exposure. In addition, culturing BBMECs with C6 conditioned medium (CM) had no effect on the localization of E-cadherin. Western blotting experiments showed that BBMECs express E-cadherin and this protein is decreased in a time dependent manner after various hypoxic/aglycemic exposures when endothelial cells are cultured alone or with C6 astrogliomas grown on a separate culture surface. When C6 astrocytes are grown directly opposed to endothelial cells, with a porous membrane between, we observed a slight attenuation in the decreased BBMEC expression of E-Cadherin after hypoxia/aglycemia exposure. This work has shown that the mammalian brain endothelial/astrocyte co-culture system is a useful model for studies of pathological conditions where BBB characteristics are maintained.

N-cadherin at the glial scar in the rat

Following injury to the central nervous system (CNS), astrocytes become reactive and in many cases form a glial scar. Very little is known about the adhesive interactions between astrocytes at the glial scar, even though reactive gliosis and scar formation are a central issue in CNS wound healing. In the present study, we examine the role of cadherin in the process of scar formation using immunohistochemistry and immunoblot methods. When a stab wound was made in the cerebral cortex of the rat, cadherins were consistently upregulated by the reactive astrocytes at the glial scar. Our immunoblot analysis demonstrates that the increase in cadherin immunoreactivity was due to a threefold upregulation of a single protein with a molecular weight of 135 kDa. The size (135 kDa) and location of the immunoreactive protein at regions of cell-cell contact in cultured astrocytes indicates that the immunoreactive protein is N-cadherin. These data are the first to demonstrate that N-cadherin plays a prominent role in the response of astrocytes to injury, including the formation and maintenance of the glial scar.

Differential localization of VE- and N-cadherins in human endothelial cells: VE-cadherin competes with N-cadherin for junctional localization

The two major cadherins of endothelial cells are neural (N)-cadherin and vascular endothelial (VE)- cadherin. Despite similar level of protein expression only VE-cadherin is located at cell-cell contacts, whereas N-cadherin is distributed over the whole cell membrane. Cotransfection of VE-cadherin and N-cadherin in CHO cells resulted in the same distribution as that observed in endothelial cells indicating that the behavior of the two cadherins was not cell specific but related to their structural characteristics. Similar amounts of alpha- and beta-catenins and plakoglobin were associated to VE- and N-cadherins, whereas p120 was higher in the VE-cadherin complex. The presence of VE-cadherin did not affect N-cadherin homotypic adhesive properties or its capacity to localize at junctions when cotransfectants were cocultured with cells transfected with N-cadherin only. To define the molecular domain responsible for the VE-cadherin-dominant activity we prepared a chimeric construct formed by VE-cadherin extracellular region linked to N-cadherin intracellular domain. The chimera lost the capacity to exclude N-cadherin from junctions indicating that the extracellular domain of VE-cadherin alone is not sufficient for the preferential localization of the molecule at the junctions. A truncated mutant of VE-cadherin retaining the full extracellular domain and a short cytoplasmic tail (Arg621-Pro702) lacking the catenin-binding region was able to exclude N-cadherin from junctions. This indicates that the Arg621-Pro702 sequence in the VE-cadherin cytoplasmic tail is required for N-cadherin exclusion from junctions. Competition between cadherins for their clustering at intercellular junctions in the same cell has never been described before. We speculate that, in the endothelium, VE- and N-cadherin play different roles; whereas VE-cadherin mostly promotes the homotypic interaction between endothelial cells, N-cadherin may be responsible for the anchorage of the endothelium to other surrounding cell types expressing N-cadherin such as vascular smooth muscle cells or pericytes.

An increase in intracellular [Na+] during Ca2+ depletion is not related to Ca2+ paradox damage in rat hearts

Ca2+ paradox damage has been suggested to be determined by Na+ entry during Ca2+ depletion and exchange of Na+ for Ca2+ during Ca2+ repletion. With the use of 23Na nuclear magnetic resonance, we previously observed a Ca2+ paradox without a prior Na+ increase. We have now demonstrated a Na+ increase during Ca2+ and Mg2+ depletion without the occurrence of the Ca2+ paradox during Ca2+ repletion. Isolated rat hearts were perfused for 20 min with a Ca(2+)-free or a Ca(2+)- and Mg(2+)-free (Ca2+/Mg(2+)-free) solution under hypothermic conditions (20 and 25 degrees C). Intracellular Na+ concentration ([Na+]i) increased from 11.9 +/- 1.2 to 26.9 +/- 5.8 mM (P < 0.001) during Ca2+/Mg(2+)-free perfusion at 20 degrees C, whereas no significant change in [Na+]i occurred during 20 min of Ca(2+)-free perfusion at 20 degrees C. In addition, we confirmed that [Na+]i did not change significantly during 20 min of normothermic Ca(2+)-free perfusion. Creatine kinase release during normothermic Ca2+ repletion in the 20 degrees C groups was approximately 10% and in the 25 degrees C groups 75% of the release in the normothermia group. Recovery of rate-pressure product was approximately 50% in the 20 degrees C groups versus 0% in the normothermia group. In conclusion, hypothermic Ca2+/Mg(2+)-free perfusion results in a significant increase of [Na+]i, which does not contribute to the extent of the Ca2+ paradox on normothermic Ca2+ repletion.

Molecular and functional analysis of cadherin-based adherens junctions

Adherens junctions are specialized forms of cadherin-based adhesive contacts important for tissue organization in developing and adult organisms. Cadherins form protein complexes with cytoplasmic proteins (catenins) that convert the specific, homophilic-binding capacity of the extracellular domain into stable cell adhesion. The extracellular domains of cadherins form parallel dimers that possess intrinsic homophilic-binding activity. Cytoplasmic interactions can influence the function of the ectodomain by a number of potential mechanisms, including redistribution of binding sites into clusters, providing cytoskeletal anchorage, and mediating physiological regulation of cadherin function. Adherens junctions are likely to serve specific, specialized functions beyond the basic adhesive process. These functions include coupling cytoskeletal force generation to strongly adherent sites on the cell surface and the regulation of intracellular signaling events.

Ultrastructural localization of cadherin in the adult guinea-pig organ of Corti

The apices of the majority of cells of the organ of Corti are connected together by junctional complexes to form the reticular lamina, a barrier that prevents the mixing of endolymph and perilymph. These complexes include tight junctions, adherens junctions and desmosomes. Further information is required about the identity and distribution of the molecules involved in these connections if the function and organization of the reticular lamina are to be well understood. One major category of molecules occurring in adherens junctions and desmosomes, and involved in the maintenance of tissue integrity, is the cadherins. However, although cadherin has been identified in junctions between supporting cells in the adult mammalian organ of Corti at the light microscopic level, its ultrastructural distribution has not so far been described. A post-embedding immunogold labelling technique has therefore been used in conjunction with a monoclonal antibody to cadherin to investigate its ultrastructural distribution in the adult guinea-pig reticular lamina. Immunolabelling is observed in hair cell-supporting cell junctions and in supporting cell-supporting cell junctions. In addition, there is more labelling associated with inner hair cell-supporting cell junctions than with outer hair cell-supporting cell junctions. This may indicate that the junctions associated with the two types of hair cell have different functional properties.

Cellular and molecular features of lens differentiation: a review of recent advances

In this paper, the more recent literature pertaining to differentiation in the developing vertebrate lens is reviewed in relation to previous work. The literature reviewed reveals that the developing lens has been, and will continue to be, a useful model system for the examination of many fundamental processes occurring during embryonic development. Areas of lens development reviewed here include: the induction and early embryology of the lens; lens cell culture techniques; the role of growth factors and cytokines; the involvement of gap junctions in lens cell-cell communication; the role of cell adhesion molecules, integrins, and the extracellular matrix; the role of the cytoskeleton; the processes of programmed cell death (apoptosis) and lens fibre cell denucleation; the involvement of Pax and Homeobox genes; and crystallin gene regulation. Finally, some speculation is provided as to possible directions for further research in lens development.

The catenin/cadherin adhesion system is localized in synaptic junctions bordering transmitter release zones

Molecular mechanisms linking pre- and postsynaptic membranes at the interneuronal synapses are little known. We tested the cadherin adhesion system for its localization in synapses of mouse and chick brains. We found that two classes of cadherin-associated proteins, alpha N- and beta-catenin, are broadly distributed in adult brains, colocalizing with a synaptic marker, synaptophysin. At the ultrastructural level, these proteins were localized in synaptic junctions of various types, forming a symmetrical adhesion structure. These structures sharply bordered the transmitter release sites associated with synaptic vesicles, although their segregation was less clear in certain types of synapses. N-cadherin was also localized at a similar site of synaptic junctions but in restricted brain nuclei. In developing synapses, the catenin-bearing contacts dominated their junctional structures. These findings demonstrate that interneuronal synaptic junctions comprise two subdomains, transmitter release zone and catenin-based adherens junction. The catenins localized in these junctions are likely associated with certain cadherin molecules including N-cadherin, and the cadherin/ catenin complex may play a critical role in the formation or maintenance of synaptic junctions.

A model for central synaptic junctional complex formation based on the differential adhesive specificities of the cadherins

Cadherins control critical developmental events through well-documented homophilic interactions. In epithelia, they are hallmark constituents of junctions that mediate intercellular adhesion. Brain tissue expresses several cadherins, and we now show that two of these, neural (N)- and epithelial (E)-cadherin, are localized to synaptic complexes in mutually exclusive distributions. In cerebellum, N-cadherin is frequently found associated with synapses, some of which are perforated, and in hippocampus, N- and E-cadherin-containing synapses are found aligned along dendritic shafts within the stratum lucidum of CA3. We propose that the cadherins function as primary adhesive moieties between pre- and postsynaptic membranes in the synaptic complex. According to this model, once neurites have been guided to the vicinity of their cognate targets, it is the differential distribution of cadherins along the axonal and dendritic plasma membranes, and ultimately cadherin self-association, that "locks in" nascent synaptic connections.

Focal expression of A-CAM on pillar cells during formation of Corti's tunnel in gerbil cochlea

BACKGROUND

The organ of Corti in the mammalian cochlea develops from a simple epithelium into a complex structure consisting of as many as ten highly specialized cell types. The purpose of the present study was to examine the possible role of a cell adhesion specific molecule (A-CAM) in mediating morphogenesis of the organ of Corti.

METHOD

The expression of A-CAM was studied in a series of inner ears collected from neonatal gerbils at two days intervals from 0 to twenty days after birth. Immunostaining was performed with a mouse monoclonal antibody raised against A-CAM isolated from chicken cardiac muscle.

RESULTS

The adhesion molecule appeared just prior to opening of the tunnel of Corti and disappeared after full expansion of tunnel space. A-CAM was detected in the basal turn of the cochlea as early as two days after birth and its expression moved progressively toward the apex of the cochlear spiral. It was observed in all three cochlear turns at eight days after birth but disappeared after postnatal day twelve. Immunostaining for A-CAM was localized only to the region where inner and outer pillar cells separate to form the tunnel of Corti.

CONCLUSIONS

A-CAM apparently plays a role in the formation of the tunnel space by modulating apical adhesion above the separation between inner and outer pillar cells.

Adhesion molecules as determinants of disease: from molecular biology to surgical research

Cellular adhesion is mediated by distinct cell surface receptors (adhesion molecules) and plays a pivotal role in the biological processes of morphogenesis, cell migration and cell-cell communication. During the past decade many adhesion molecules have been identified and structurally analysed. This has allowed an understanding of their role in the pathophysiology of disease, including inflammation and sepsis, ischaemia and reperfusion, transplant rejection, atherosclerosis and thrombosis, angiogenesis and wound healing, as well as carcinogenesis and tumour metastasis. Understanding of the molecular mechanisms of cellular communication is not only vital for advances in surgical pathophysiology, it also has the potential to widen the spectrum of diagnosis and therapy of disease. Analysis of expression of individual surface molecules may help in the diagnosis of transplant rejection and allow a prognostic determination of tumour progression and metastasis formation. Moreover, manipulation of adhesion molecule function by monoclonal antibodies, antisense oligonucleotides or single gene products may open the door for novel therapeutic regimens to prevent transplant rejection and ischaemia-, sepsis- and shock-induced tissue injury.

Generation of new intercellular junctions between cardiocytes. A possible mechanism compensating for mechanical overload in the hypertrophied human adult myocardium

Intercellular dehiscence is a common cardiocytic response to pathological conditions. However, little consideration has been given to the possibility of new intercellular junctions developing between cardiocytes within developed myocardium. To examine this possibility as it may relate to useful compensation for hemodynamic overloads, changes in cardiocytic connection were evaluated by scanning electron microscopy in hypertrophied myocardium of adult human hearts. Transmural myocardium of left ventricle was obtained at autopsy from five hearts with concentric hypertrophy, five hearts with eccentric hypertrophy, and five control hearts (noncardiac death). After formalin fixation, the number of cardiocytes connected to an individual cardiocyte was counted in tissues from the middle portion of the transmural samples by scanning electron microscopy. Cardiocytic diameter and connective tissue volume fraction were measured on the transmural sections by light microscopy. In concentrically hypertrophied hearts present both increased cardiocytic diameter and connective tissue volume fraction, the number of other cardiocytes connected to an individual cardiocyte (4.60 +/- 0.10 [mean +/- SE] was significantly increased (P < .05) compared with control hearts (4.19 +/- 0.12) or eccentrically hypertrophied hearts (4.11 +/- 0.10). The increase in junctions per cardiocyte in concentrically hypertrophied hearts suggests that new connections had been generated. More junctions developing during hypertrophy could add another structural advantage to those of cardiocytic hypertrophy and connective tissue proliferation as compensatory adjustments to hemodynamic overload in concentrically hypertrophied hearts.