Modulation of epithelial morphogenesis and cell fate by cell-to-cell signals and regulated cell adhesion

Cell-cell and cell-extracellular matrix (ECM) interactions control many developmental decisions of epithelial cell fate and morphogenesis. Protein tyrosine kinases are one class of regulatory molecules that have been implicated in the modulation of these processes. Several protein tyrosine kinases co-localize with cell-cell (cadherin) and cell-ECM (integrin) adhesion molecules at specific adhesion domains of epithelial cells. Protein tyrosine kinases may regulate epithelial development by modulating cell-cell and cell-ECM interactions and by relaying signals initiated by these interactions to other cellular components that determine cell structure and function.     

Diversity of probiotic adhesion genes in the gastrointestinal tract of goats

Gastrointestinal (GI) microflora is an important system in the host, as it has both pathogenic and probiotic bacteria. Most of the studies were focused on the human gut microflora and the available information on the intestinal microflora of goats was limited. This urged the need to inspect the impacts of the goat's gut microflora. Metagenomic investigation of probiotic bacteria in the GI tract of goat is one of the challenging streams because of the less available data of the uncultivable bacteria. In our report, comparative analysis of metagenomic and enrichment samples of goat intestinal content was done and this approach will be helpful in analyzing the identification of uncultivable and cultivable probiotic bacteria. This study mainly focused on three key probiotic adhesion genes, such as EF-Tu, mapA, and mub. The GI of four different goats were investigated for these genes. The data from this study showed that there is a wide diversity of these genes among goat intestinal samples.     

Covalently bound fatty acids in the gastrointestinal epithelial cell membrane.

Myristic, palmitic, stearic, oleic and linoleic acids have been identified as the covalently bound fatty acids in the monkey gastrointestinal mucosal membrane proteins and among them palmitolation was predominant. Distribution studies in various regions of the gastrointestinal mucosa showed no significant difference in the content and composition of covalently bound fatty acids in these membrane and most of the fatty acids were found to be ester linked. Total membranes from isolated crypt and villus enterocytes and colonocytes had similar composition of these fatty acids. Covalently bound fatty acid levels were higher in the small intestinal brush border membrane. As suggested for the mucus glycoproteins, covalently bound fatty acids in the intestinal epithelial cell membrane may protect these membranes from proteolytic damage from the luminal proteases.     

Taste receptors in the gastrointestinal tract. V. Acid sensing in the gastrointestinal tract

Luminal acidity is a physiological challenge in the foregut, and acidosis can occur throughout the gastrointestinal tract as a result of inflammation or ischemia. These conditions are surveyed by an elaborate network of acid-governed mechanisms to maintain homeostasis. Deviations from physiological values of extracellular pH are monitored by multiple acid sensors expressed by epithelial cells and sensory neurons. Acid-sensing ion channels are activated by moderate acidification, whereas transient receptor potential ion channels of the vanilloid subtype are gated by severe acidosis. Some ionotropic purinoceptor ion channels and two-pore domain background K(+) channels are also sensitive to alterations of extracellular pH.     

Immunolocalization of the neural cell adhesion molecule L1 in non-proliferating epithelial cells of the male urogenital tract

The localization of the neural cell adhesion molecule L1 in the male urogenital tract (including seminal vesicles and prostate) of the mouse and bull was investigated using immunocytochemical and immunochemical methods in order to better understand the function of this glycoprotein in non-neural tissues. L1 antibodies labeled non-myelinated nerves in all portions of the urogenital tract investigated. However, L1 immunoreactivity was also found between epithelial cells of several regions of the urogenital system including epididymal tail, deferent duct, ejaculatory duct and seminal vesicles. Some L1 immunoreactivity was also demonstrated between epithelial cells of murine urinary bladder and urethra. The specificity of the immunoreaction was verified by western blots. There was no correlation between L1 expression and proliferating activity as revealed by double immunocytochemistry using various markers of cell proliferation. This unexpected expression of L1 in nonneural tissue is mainly restricted to non-proliferating epithelia of those portions of the urogenital tract that are derived from the Wolffian duct. It is suggested that L1 in these epithelia could enhance the mechanical resistance and reduce transepithelial permeability.     

Glycoconjugate and adhesion molecule changes during the cell cycle in a human embryonic epithelial cell line

The changes in the expression of glycoconjugates and adhesion molecules were studied by selective lectin binding and immunocytochemical reactions in a human embryonic epithelial cell line (EUE cells), synchronized in the cell cycle phases. The results can be summarized as follows: most of the tested lectins display a more diffuse binding for the cytoplasm in G₁ than S and G₂ phases; in the S and particularly in G₂ phases the cytoplasm glycoconjugates are rearranged around the nucleus; cells in mitosis always show a strong binding towards all tested lectins. Cellular fibronectin and its receptor β₁ integrin are well expressed in G₁, but the strongest reaction is observed in the S phase. The immunoreactions for laminin and uvomorulin (L-CAM) are poorly positive in all cell cycle phases. The immunocytochemical reaction for heparan sulfate is positive, with a stronger reaction in S and G₂ than in G₁; on the contrary a diffuse staining with the anti-dermatan sulfate proteoglycan antibody appears unchanged during the cell cycle.     

Polyamines regulate Rho-kinase and myosin phosphorylation during intestinal epithelial restitution

Polyamines are required for the early phase of mucosal restitution that occurs as a consequence of epithelial cell migration. Our previous studies have shown that polyamines increase RhoA activity by elevating cytosolic free Ca(2+) concentration ([Ca(2+)](cyt)) through controlling voltage-gated K(+) channel expression and membrane potential (E(m)) during intestinal epithelial restitution. The current study went further to determine whether increased RhoA following elevated [Ca(2+)](cyt) activates Rho-kinase (ROK/ROCK) resulting in myosin light chain (MLC) phosphorylation. Studies were conducted in stable Cdx2-transfected intestinal epithelial cells (IEC-Cdx2L1), which were associated with a highly differentiated phenotype. Reduced [Ca(2+)](cyt), by either polyamine depletion or exposure to the Ca(2+)-free medium, decreased RhoA protein expression, which was paralleled by significant decreases in GTP-bound RhoA, ROCK-1, and ROKalpha proteins, Rho-kinase activity, and MLC phosphorylation. The reduction of [Ca(2+)](cyt) also inhibited cell migration after wounding. Elevation of [Ca(2+)](cyt) induced by the Ca(2+) ionophore ionomycin increased GTP-bound RhoA, ROCK-1, and ROKalpha proteins, Rho-kinase activity, and MLC phosphorylation. Inhibition of RhoA function by a dominant negative mutant RhoA decreased the Rho-kinase activity and resulted in cytoskeletal reorganization. Inhibition of ROK/ROCK activity by the specific inhibitor Y-27632 not only decreased MLC phosphorylation but also suppressed cell migration. These results indicate that increase in GTP-bound RhoA by polyamines via [Ca(2+)](cyt) can interact with and activate Rho-kinase during intestinal epithelial restitution. Activation of Rho-kinase results in increased MLC phosphorylation, leading to the stimulation of myosin stress fiber formation and cell migration.     

Mucosal dendritic cell diversity in the gastrointestinal tract

The discovery of dendritic cells (DCs) in skin by Paul Langerhans in 1868 identified a cell type which has since been recognized as a key link between innate and adaptive immunity. DCs originate from bone marrow and disseminate through blood to all tissues in the body, and distinct DC subpopulations have been identified in many different tissues. DC diversity is apparent throughout all mucosal surfaces of the body, but the focus of this review article is DC diversity throughout the gastro-intestinal tract (GIT). DC subpopulations have been well characterized in the oral cavity and small intestine, but DC characterization in other regions, such as the esophagus and stomach, is limited. Substantial research has focused on DC function during disease, but understanding the regulation of inflammation and the induction of acquired immune responses requires combined phenotypic and functional characterization of individual DC subpopulations. Furthermore, little is known regarding mucosal DC subpopulations in the GIT of the neonate and how these DC populations change following colonization by commensal microflora. The current review will highlight mucosal DC diversity and discuss factors that may influence mucosal DC differentiation.     

Dynamic actin-based epithelial adhesion and cell matching during Drosophila dorsal closure

BACKGROUND: The adhesion of two epithelial sheets is a fundamental process that occurs throughout embryogenesis and during wound repair. Sealing of the dorsal epidermis along the midline of the Drosophila embryo provides a genetically tractable model to analyse the closure of such holes. Several studies indicate that the actin cytoskeleton plays a critical role in dorsal closure. Although many components of the signalling cascade directing this process have been identified, the precise cell-biological events upon which these signals act remain poorly described. RESULTS: By confocal imaging of living fly embryos expressing green fluorescent protein (GFP)-tagged actin, we found that dorsal closure relies on the activity of dynamic filopodia and lamellipodia that extend from front-row cells to actively zipper the epithelial sheets together. As these epithelial fronts approach one another, we observed long, thin filopodia, apparently 'sampling' cells on the opposing face. When the assembly of these actin-based protrusions was blocked (by interfering with the activities of Cdc42 and Jun N-terminal kinase signalling), the adhesion and fusion of opposing epithelial cells was prevented and their ability to 'sense' correct partners was also blocked, leading to segment misalignment along the midline seam. CONCLUSIONS: Dynamic, actin-based protrusions (filopodia and lamellae) are critical, both in the mechanics of epithelial adhesion during dorsal closure and in the correct 'matching' of opposing cells along the fusion seam.     

Modulation of Rac1 and ARF6 activation during epithelial cell scattering

Epithelial cell scattering encompasses the dissolution of intercellular junctions, cell-cell dissociation, cell spreading, and motility. The Rac1 and ARF6 GTPases have been shown to regulate one or more of these aforementioned processes. In fact, activated Rac1 has been shown to promote cell-cell adhesion as well as to enhance cell motility, leading to conflicting reports on the effect of Rac1 activation on epithelial cell motility. In this study, we have examined the activation profiles of endogenous Rac1 and ARF6 during the sequential stages of epithelial cell scattering. Using Madin-Darby canine kidney cells treated with hepatocyte growth factor/scatter factor or cell lines stably expressing activated v-Src, we show that Rac1 and ARF6 exhibit distinct activation profiles during cell scattering. We have found that an initial ARF6-dependent decrease in the levels of Rac1-GTP is necessary to induce cell-cell dissociation. This is followed by a steady increase in Rac1 and ARF6 activation and cell migration. In sum, this study documents the progression of ARF6 and Rac1 activities during epithelial cell scattering.     

Thyrotropin-releasing hormone in the gastrointestinal tract.

TRH immunoreactivity has been shown to occur throughout the rat gastrointestinal tract. This immunoreactivity demonstrates parallelism with TRH, is destroyed by fresh human serum, and co-chromatographs with TRH on a Sephadex G-10 column and on a SP Sephadex C-25 column. In addition pancreatic extracts showed bioactivity in a mouse bioassay for TRH.     

Gene transfer in the gastrointestinal tract.

The maximum in vivo transfer rate of plasmid pAMbeta1 in the gut was 0.03 transconjugant per recipient cell, and this rate could be simulated in vitro only by forced filter mating. Transfer was not detected in liquid culture matings. Our findings demonstrate that in vitro methods, such as forced filter mating and liquid mating, underestimate the in vivo rates of gene transfer.     

A novel cell surface antigen involved in thymocyte and thymic epithelial cell adhesion.

A murine mAb, 7D3, was produced by fusion of spleen cells obtained from mice immunized with a rat thymic epithelial cell line, Tu-D3 and NS/1 myeloma cells. 7D3 antibody reacted with approximately 95% thymocytes, 17% spleen cells, less than 9% of mesenteric lymph node cells and 32% of bone marrow cells of rat origin. 7D3 also reacted with two rat thymic epithelial cell lines but not with a rat fibroblastic cell line. Immunochemical analysis demonstrated that 7D3 antibody recognized a single polypeptide with molecular weight of 80,000 in FTE cells and 80,000 to 96,000 in thymocytes. 7D3 antibody strongly inhibited the thymocyte binding to thymic epithelial cells. In addition, 7D3 antibody inhibited TPA-induced thymocyte aggregation. 7D3 negative rat thymic lymphoma cells bound to 7D3 positive thymic epithelial cells and this binding was inhibited by 7D3 antibody, indicating that a part of thymocyte-thymic epithelial cell binding was mediated by the interaction of 7D3 Ag and undefined ligand to 7D3.     

N-acetyl-cysteine enhances cell adhesion properties of epithelial and lymphoid cells.

In this paper, we show that the antioxidant N-acetyl-cysteine (NAC) is capable of enhancing the adhesion properties of the epithelial cell line A431 and of the lymphocytic cells with cytotoxic activitv from human peripheral blood: the natural killer (NK) cells. This effect leads to an increased efficiency of A431 cells to form a monolayer and of NK cells to kill their targets. In both cases a specific effect of NAC was found in the distribution of those molecules of the cytoskeleton which are generally involved in cell substrate and cell-to-cell contact region formation, e.g., the actin microfilaments. NAC could thus behave as a drug influencing certain cytoskeleton-dependent cell processes in a non-histotype dependent manner.     

Modulation of Drosophila retinal epithelial integrity by the adhesion proteins capricious and tartan

Background

The development of the Drosophila eye imaginal disc requires complex epithelial rearrangements. Cells of the morphogenetic furrow are apically constricted and this leads to a physical indentation in the epithelium. Posterior to the furrow, cells start to rearrange into distinct clusters and eventually form a precisely patterned array of ommatidia. These morphogenetic processes include regulated changes of adhesion between cells.

Methodology/Principal Findings

Here, we show that two transmembrane adhesion proteins, Capricious and Tartan, have dynamic and complementary expression patterns in the eye imaginal disc. We also describe novel null mutations in capricious and double null mutations in capricious and tartan. We report that they have redundant functions in regulating the architecture of the morphogenetic furrow and ommatidial spacing.

Conclusions/Significance

We conclude that Capricious and Tartan contribute to the adhesive properties of the cells in the morphogenetic furrow and that this regulated adhesion participates in the control of spacing ommatidial clusters.     

scabrous modifies epithelial cell adhesion and extends the range of lateral signalling during development of the spaced bristle pattern in Drosophila.

The role of scabrous (sca) in the evenly spaced bristle pattern of Drosophila is explored. Loss-of-function of sca results in development of an excess of bristles. Segregation of alternately spaced bristle precursors and epidermal cells from a group of equipotential cells relies on lateral inhibition mediated by Notch and Delta (Dl). In this process, presumptive bristle precursors inhibit the neural fate of neighbouring cells, causing them to adopt the epidermal fate. We show that Dl, a membrane-bound ligand for Notch, can inhibit adjacent cells, in direct contact with the precursor, in the absence of Sca. In contrast, inhibition of cells not adjacent to the precursor requires, in addition, Sca, a secreted molecule with a fibrinogen-related domain. Over-expression of Sca in a wild-type background, leads to increased spacing between bristles, suggesting that the range of signalling has been increased. scabrous acts nonautonomously, and we present evidence that, during bristle precursor segregation, Sca is required to maintain the normal adhesive properties of epithelial cells. The possible effects of such changes on the range of signalling are discussed. We also show that the sensory organ precursors extend numerous fine cytoplasmic extensions bearing Dl molecules, and speculate on a possible role for these structures during signalling.