Distribution of E-cadherin and β-catenin in relation to cell maturation and cell extrusion in rat and mouse small intestines

Pulsatile contractility of actomyosin networks organizes the cellular cortex at lateral cadherin junctions

The physical properties of cells reflect how the structure and dynamics of the actomyosin cortex are coupled to the plasma membrane. In epithelia, adhesive E-cadherin clusters associate with the cell cortex to assemble the junctional actomyosin that participates in epithelial morphogenesis. E-cadherin is present not only at the apical zonula adherens (ZA), but also distributed throughout the lateral adherens junction (LAJ) below the ZA. However, the organizational dynamics of the actomyosin network at the LAJs remains elusive. To address this, we used quantitative real-time imaging to characterize the dynamics of actomyosin contractility at lateral cadherin contacts. Here, we report that contractility is coordinated into smaller actomyosin rings that link cadherin clusters together within the larger cortical network at the lateral junctions. We conclude that Myosin II activity determines the contractility of actomyosin cables between cadherin clusters to propagate pulsatility across lateral cell-cell contacts.

Immunohistological characterization of intercellular junction proteins in rhesus macaque intestine

Epithelial junctions play an important role in regulating paracellular permeability and intercellular adhesion. It has been reported that changes in the density of epithelial junctions and/or distribution pattern can contribute to various gastrointestinal (GI) disorders. In this study, we investigated the distribution of the tight junction (Claudins. 1, 3, 4, 5, 7, 10, Zonula Occludens (ZO-1), Occludin), adherens junction (E-cadherin), desmosome (Desmoglein 2, Desmocollin 2) and gap junction (Connexin 43) proteins in the jejunum, ileum and colonic epithelium of healthy rhesus macaques (RM) using immunofluorescence labeling. While proteins in these respective junctions were expressed throughout the jejunum, ileum and colon of RM, we observed differential labeling in epithelial cells from these sites. Claudins 1, 3, 4, 7, E-cadherin and Desmoglein 2 were distributed in the respective intercellular junctions with additional labeling in the lateral membrane of epithelial cells in both small and large intestine. However, claudin 5, claudin 10, ZO-1 and occludin showed uniform distribution in the intercellular junctions of crypt and surface epithelial cells of the intestine. Desmocollin 2 localized predominantly in the upper two thirds along the lateral membrane while desmoglein 2 was distributed along the entire lateral membrane of intestinal epithelial cells. In contrast, connexin 43 exhibited punctate lateral labeling in crypt epithelial cells of the small and large intestine. Our results show diverse localization of epithelial intercellular junction proteins along the intestinal tract of RM. These findings may correlate with differences in paracellular permeability and adhesion along the intestinal tract and could correlate with pathologic disease in these regions of the intestine.

Cortical F-actin stabilization generates apical-lateral patterns of junctional contractility that integrate cells into epithelia

E-cadherin cell-cell junctions couple the contractile cortices of epithelial cells together, generating tension within junctions that influences tissue organization. Although junctional tension is commonly studied at the apical zonula adherens, we now report that E-cadherin adhesions induce the contractile actomyosin cortex throughout the apical-lateral axis of junctions. However, cells establish distinct regions of contractile activity even within individual contacts, producing high tension at the zonula adherens but substantially lower tension elsewhere. We demonstrate that N-WASP (also known as WASL) enhances apical junctional tension by stabilizing local F-actin networks, which otherwise undergo stress-induced turnover. Further, we find that cells are extruded from monolayers when this pattern of intra-junctional contractility is disturbed, either when N-WASP redistributes into lateral junctions in H-Ras(V12)-expressing cells or on mosaic redistribution of active N-WASP itself. We propose that local control of actin filament stability regulates the landscape of intra-junctional contractility to determine whether or not cells integrate into epithelial populations.

Patterns in space: coordinating adhesion and actomyosin contractility at E-cadherin junctions

Cadherin adhesion receptors are fundamental determinants of tissue organization in health and disease. Increasingly, we have come to appreciate that classical cadherins exert their biological actions through active cooperation with the contractile actin cytoskeleton. Rather than being passive resistors of detachment forces, cadherins can regulate the assembly and mechanics of the contractile apparatus itself. Moreover, coordinate spatial patterning of adhesion and contractility is emerging as a determinant of morphogenesis. Here we review recent developments in cadherins and actin cytoskeleton cooperativity, by focusing on E-cadherin adhesive patterning in the epithelia. Next, we discuss the underlying principles of cellular rearrangement during Drosophila germband extension and epithelial cell extrusion, as models of how planar and apical-lateral patterns of contractility organize tissue architecture.

Epidermal growth factor receptor is involved in enterocyte anoikis through the dismantling of E-cadherin-mediated junctions

Enterocytes of the intestinal epithelium are continually regenerated. They arise from precursor cells in crypts, migrate along villi, and finally die, 3-4 days later, when they reach the villus apex. Their death is thought to occur by anoikis, a form of apoptosis induced by cell detachment, but the mechanism of this process remains poorly understood. We have previously shown that a key event in the onset of anoikis in normal enterocytes detached from the basal lamina is the disruption of adherens junctions mediated by E-cadherin (Fouquet S, Lugo-Martinez VH, Faussat AM, Renaud F, Cardot P, Chambaz J, Pincon-Raymond M, Thenet S. J Biol Chem 279: 43061-43069, 2004). Here we have further investigated the mechanisms underlying this disassembly of the adherens junctions. We show that disruption of the junctions occurs through endocytosis of E-cadherin and that this process depends on the tyrosine-kinase activity of the epidermal growth factor receptor (EGFR). Activation of EGFR was detected in detached enterocytes before E-cadherin disappearance. Specific inhibition of EGFR by tyrphostin AG-1478 maintained E-cadherin and its cytoplasmic partners beta- and alpha-catenin at cell-cell contacts and decreased anoikis. Finally, EGFR activation was evidenced in the intestinal epithelium in vivo, in rare individual cells, which were shown to lose their interactions with the basal lamina. We conclude that EGFR is activated as enterocytes become detached from the basal lamina, and that this mechanism contributes to the disruption of E-cadherin-dependent junctions leading to anoikis. This suggests that EGFR participates in the physiological elimination of the enterocytes.

Recent progress in histochemistry

The progress in discerning the structure and function of cells and tissues in health and disease has been achieved to a large extent by the continued development of new reagents for histochemistry, the improvement of existing techniques and new imaging techniques. This review will highlight some advancements made in these fields.

The histochemistry and cell biology vade mecum: a review of 2005–2006

The procurement of new knowledge and understanding in the ever expanding discipline of cell biology continues to advance at a breakneck pace. The progress in discerning the physiology of cells and tissues in health and disease has been driven to a large extent by the continued development of new probes and imaging techniques. The recent introduction of semi-conductor quantum dots as stable, specific markers for both fluorescence light microscopy and electron microscopy, as well as a virtual treasure-trove of new fluorescent proteins, has in conjunction with newly introduced spectral imaging systems, opened vistas into the seemingly unlimited possibilities for experimental design. Although it oftentimes proves difficult to predict what the future will hold with respect to advances in disciplines such as cell biology and histochemistry, it is facile to look back on what has already occurred. In this spirit, this review will highlight some advancements made in these areas in the past 2 years.