Affinity of red blood cell membrane for particle surfaces measured by the extent of particle encapsulation.

An experimental technique and a simple analysis are presented that can be used to quantitate the affinity of red blood cell membrane for surfaces of small beads or microsomal particles up to 3 micrometers Diam. The technique is demonstrated with an example of dextran-mediated adhesion of small spherical red cell fragments to normal red blood cells. Cells and particles are positioned for contact by manipulation with glass micropipets. The mechanical equilibrium of the adhesive contact is represented by the variational expression that the decrease in interfacial free energy due to a virtual increase in contact area is balanced by the increase in elastic energy of the membrane due to virtual deformation. The surface affinity is the reduction in free energy per unit area of the interface associated with the formation of adhesive contact. From numerical computations of equilibrium configurations, the surface affinity is derived as a function of the fractional extent of particle encapsulation. The range of surface affinities for which the results are applicable is increased over previous techniques to several times the value of the elastic shear modulus. It is shown that bending rigidity of the membrane has little effect on the analytical results for particles 1--3 micrometers Diam and that results are essentially the same for both cup- and disk-shaped red cells. A simple analytical model is shown to give a good approximation for surface affinity (normalized by the elastic shear modulus) as a function of the fractional extent of particle encapsulation. The model predicts that a particle would be almost completely vacuolized for surface affinities greater than or equal to 10 times the elastic shear modulus. Based on an elastic shear modulus of 6.6 x 10(-3) dyn/cm, the range for the red cell-particle surface affinity as measured by this technique is from approximately 7 x 10(-4) to 7 x 10(-2) erg/cm2. Also, an approximate relation is derived for the level of surface affinity necessary to produce particle vacuolization by a phospholipid bilayer surface which possesses bending rigidity and a fixed tension.     

Characteristics of the adhesive determinants of Lactobacillus fermentum 104.

The adhesion of Lactobacillus fermentum 104-R and the variant strain 104-S to porcine gastric squamous epithelium was investigated. An epithelium-specific adhesion was detected for strain 104-S; however, strain 104-R expressed enhanced adhesion capacity to the control surfaces of polystyrene and bovine serum albumin. To characterize the adhesive determinants, the bacterial cells were exposed to various treatments. The adhesion pattern of bacterial cells in buffers of pH values ranging from 2 to 7 was determined. The adhesion of strain 104-S to epithelium was greater in a buffer with a higher pH value. On the other hand, adhesion of strain 104-R to the epithelium was rather unaffected by a change in pH. To the control surfaces of polystyrene or bovine serum albumin, the adhesion of both strains was greatest at pH 2 to 4. Treatment of strain 104-S with metaperiodate did not affect the adhesion to epithelium or polystyrene; however, protease treatment dramatically decreased the adhesion of both strains, thus suggesting that the determinants responsible for the adhesion were proteinaceous. Carbohydrates may be partially involved in the adhesion of 104-R because metaperiodate-treated cells adhered more poorly than control, iodate-treated cells. The adhesion-promoting components are most probably tightly bound to the cell wall, because washing with low-pH buffer (pH 1.2) or sodium dodecyl sulfate had no major effect on the adhesion.     

Characteristics of the adhesive determinants of Lactobacillus fermentum 104

The adhesion of Lactobacillus fermentum 104-R and the variant strain 104-S to porcine gastric squamous epithelium was investigated. An epithelium-specific adhesion was detected for strain 104-S; however, strain 104-R expressed enhanced adhesion capacity to the control surfaces of polystyrene and bovine serum albumin. To characterize the adhesive determinants, the bacterial cells were exposed to various treatments. The adhesion pattern of bacterial cells in buffers of pH values ranging from 2 to 7 was determined. The adhesion of strain 104-S to epithelium was greater in a buffer with a higher pH value. On the other hand, adhesion of strain 104-R to the epithelium was rather unaffected by a change in pH. To the control surfaces of polystyrene or bovine serum albumin, the adhesion of both strains was greatest at pH 2 to 4. Treatment of strain 104-S with metaperiodate did not affect the adhesion to epithelium or polystyrene; however, protease treatment dramatically decreased the adhesion of both strains, thus suggesting that the determinants responsible for the adhesion were proteinaceous. Carbohydrates may be partially involved in the adhesion of 104-R because metaperiodate-treated cells adhered more poorly than control, iodate-treated cells. The adhesion-promoting components are most probably tightly bound to the cell wall, because washing with low-pH buffer (pH 1.2) or sodium dodecyl sulfate had no major effect on the adhesion.     

Elastic instability in growing yeast colonies

The differential adhesion between cells is believed to be the major driving force behind the formation of tissues. The idea is that an aggregate of cells minimizes the overall adhesive energy between cell surfaces. We demonstrate in a model experimental system that there exist conditions where a slowly growing tissue does not minimize this adhesive energy. A mathematical model demonstrates that the instability of a spherical shape is caused by the competition between elastic and surface energies.     

Development,cytology, lipid storage and motility of the Malpighian tubules of the nymphal dragonfly,Aeshna cyanea (Müller) (Odonata : Aeshnidae)

The Malpighian tubules of nymphal Aeshna cyanea (Odonata : Aeshnidae) were examined by light and electron microscopy. The 1st-instar nymphs have only 3 branchless tubules. With proceeding nymphal stages, these lengthen and branch. Also, additional tubules bud from the gut and show the same pattern of growth and branching, until in the final instar up to 21 separate tufts of branched tubules are present. A serpentine trachea/tracheole and a cross-striated muscle are helically wound around each tubule in close apposition. Isolated tubules show twisting movements for several days. Contraction of the muscle is responsible for fast coiling movements, while the slow decoiling movements probably depend on elastic deformations of the accompanying trachea, the basal lamina and the tubule cells, the latter showing an elaborate cytoskeleton and multiple adhesive junctions.The tubular epithelium consists of 4 types of cells. The distal segment is composed of ion transporting cells and terminates with a short, solid tip segment of undifferentiated cells. The intermediate segment consists of lipid cells which are densely filled with triglyceride droplets, as revealed by thin layer chromatography. Lipid cells are already present in the 1st instar before the nymphs have taken up any food. In later instars, the renal lipid content varies to some extent with the nutritional state and is nearly depleted during metamorphosis. The proximal segment is the region of tubular branching and may be conceived as the collecting duct of each tuft. Its epithelium consists of mucocytes.     

Physico-chemical surface characteristics and adhesive properties of Streptococcus salivarius strains with defined cell surface structures

Physico-chemical surface characteristics and adhesive properties of a series of mutants of Streptococcus salivarius HB with defined cell surface structures were determined. Zeta potentials showed no relation either with the presence or absence of specific antigens on the bacterial cell surface, or with the adhesive properties of the cells. Hydrophobicity was assessed by surface free energy determination from measured contact angles, by adsorption to hexadecane and by hydrophobic interaction chromatography. Generally, the progressive removal of fibril subclasses from the cell surface resulted in a reduced hydrophobicity. However, specific fibrillar subclasses appeared to contribute to surface hydrophobicity to widely different extents. Bacterial adhesion to polymethylmethacrylate increased with increasing hydrophobicity of the mutants. However, adhesion to a more complex biological substratum, such as saliva-coated hydroxyapatite, correlated only partly with hydrophobicity. The organism, deprived of most of its fibrillar surface structures, clearly showed the least adhesion to hydrophobic ligands, to both polymethylmethacrylate and saliva-coated hydroxyapatite, and had a significantly higher surface free energy than the other mutants and the parent strain.     

Increased adhesiveness in cultured endometrial-derived cells is related to the absence of moesin expression

Human endometrial epithelial cells (EECs) are nonadhesive for embryos throughout most of the menstrual cycle. During the so-called implantation window, the apical plasma membrane of EECs acquire adhesive properties by undergoing a series of morphological and biochemical changes. The human endometrial-derived epithelial cell line, RL95-2, serves as an in vitro model for receptive uterine epithelium because of its high adhesiveness for trophoblast-derived cells. In contrast, the HEC-1-A cell line, which displays poor adhesive properties for trophoblast cells, is considered to be less receptive. The ezrin, radixin, and moesin protein family members, which are present underneath the apical plasma membrane, potentially act to link the cytoskeleton and membrane proteins. In the present study, we have further investigated the adhesive features in these two unrelated endometrial-derived cell lines using an established in vitro model for embryonic adhesion. We have also analyzed the protein pattern and mRNA expression of ezrin and moesin in RL95-2 cells versus HEC-1-A cells. The results demonstrate that RL95-2 cells were indeed more receptive (81% blastocyst adhesion) compared with HEC-1-A cells (46% blastocyst adhesion). An intermediate adhesion rate was found in primary EECs cultured on extracellular matrix gel, thus allowing a partial polarization of these cells (67% blastocyst adhesion). Furthermore, we found that moesin was absent from RL95-2 cells. In contrast, ezrin is expressed in both cell lines, yet it is reduced in adherent RL95-2 cells. Data are in agreement with the hypothesis that uterine receptivity requires down-regulation or absence of moesin, which is a less-polarized actin cytoskeleton.     

Do rates of intercellular adhesion measure the cell affinities reflected in cell-sorting and tissue-spreading configurations?

These experiments constitute the first experimental test of the hypothesis that the rates of adhesion between cells measure the intensities of adhesion or tissue affinities that could explain cell sorting and tissue spreading. For any set of relative adhesive intensities between cells in a heterogeneous population, a corresponding minimal free energy configuration can be calculated. This is the cell distribution toward which both cell sorting and tissue spreading should lead. Equilibrium configurations were determined for combinations of 7-day embryonic retina (R) with liver (L) and heart (H), both of which became completely enveloped by R. To produce these results, the adhesive intensities would have to fall in the sequences: L-L > L-R > R-R; and H-H > H-R > R-R. To determine whether the rates of adhesion fall into these same sequences, we have devised a new technique which measures the rates of adhesion between pairs of already-formed cell aggregates of like and unlike kinds. These fall in the sequence L-L > or = H-H > L-H > R-R > H-R > L-R. If these rates paralleled the corresponding intensities of adhesion at configurational equilibrium, both L and H should have become only partially enveloped by R. Thus the rates at which adhesions are initiated do not predict the relative adhesive intensities that could explain the observed tissue configurations.     

A supramolecular theory for specificity in intracellular adhesion

This paper suggests that specificity in cell-cell adhesion may result from the supramolecular conformation or organization of cell surface adhesive molecules that may be similar or identical between cells of different adhesive affinities. A model is presented and its application to results from sea urchin gamete adhesion in vitro is discussed. In this system, we have observed that species specificity can be lost without losing adhesive capability. This suggests that specificity and adhesion reside at different levels of organization and the same or similar biochemical basis exists for gamete adhesive interactions of different species of urchins.     

Protein-mediated adhesion of Lactobacillus fermentum strain 737 to mouse stomach squamous epithelium

The mechanism of adhesion of Lactobacillus fermentum strain 737 to mouse stomach squamous epithelium was investigated. Adhesion inhibition tests involving chelators, monosaccharides, periodate and concanavalin A and the use of bacteria grown in the presence of tunicamycin failed to clarify the adhesive mechanism. Washed bacterial cells had reduced adhesive capacity, except in the presence of spent broth culture supernatant fraction or cell washings. Spent culture supernatant fractions of erythrosine-supplemented broth did not enhance adhesion of washed cells. The adhesion-promoting factor(s) in the spent broth culture supernatant fractions and cell washings bound to both bacterial and epithelial cell surfaces, but did not promote adhesion of two other Lactobacillus strains which were not of mouse origin, thereby indicating host specificity for the adhesion-promoting activity. Chemical characteristics of the adhesion-promoting factor were determined by pretreatment of the dialysis retentate of spent broth culture supernatant fractions with proteolytic enzymes, concanavalin A-Sepharose or periodate before the adhesion assay. The adhesin was non-dialysable, pronase-sensitive, heat sensitive at 100 degrees C, had no affinity for concanavalin A-Sepharose and contained no carbohydrate groups active in the adhesion process. The protein profiles of dialysis retentates of spent broth culture supernatant fractions after bacterial growth in the absence and presence of erythrosine were determined by 2-dimensional SDS-PAGE. Gel filtration by HPLC was used for purification of an adhesion-promoting fraction. The host-specific adhesion of L. fermentum strain 737 was mediated by a protein, with an Mr of 12-13000, that was not detectable in cells grown in the presence of erythrosine. A model for the mode of binding of the adhesin to host epithelia and bacterial surfaces is proposed.     

花背蟾蜍蝌蚪胃的发育形态学观察

应用大体解剖、组织切片和扫描电镜3种形态学方法对花背蟾蜍(Bufo raddei)蝌蚪在生长发育和变态过程中胃的形态结构变化进行了观察。结果显示,在蝌蚪发育24期(即G24)消化道呈简单的管状结构,胃与小肠等区分不明显,胃壁由内层矮柱状黏膜上皮细胞和其外的扁平上皮细胞层构成;直到26期胃略膨大,呈短粗管状,与小肠和食道可明显区分,胃壁内层的黏膜上皮细胞呈高柱状,上皮细胞间出现少量杯状细胞;36期的胃管明显膨大,其壁已具有胃的4层基本组织结构,杯状细胞数量增加,黏膜上皮细胞游离面有细长的微绒毛交织成网状覆盖;42期胃发育呈"C"字形,胃壁具备了消化道典型的4层结构,有胃腺芽出现,黏膜细胞的微绒毛短而直立,仅极少数细胞有长的微绒毛;蝌蚪发育到46期,肠道缩短,胃呈"J"字状,占消化道大部分,胃体中胃腺发达。在临近肝一侧,黏膜上皮细胞的微绒毛较短,胃腺少而小;而在相反一侧,微绒毛较长,胃腺多而大。基于上述结果说明,花背蟾蜍蝌蚪胃在36期已经基本完成了组织结构的分化,在变态发育期间结构和功能得到进一步完善,以适应变态后陆地生活的食性变化。     

Developmental analysis and squamous morphogenesis of the peripodial epithelium in Drosophila imaginal discs

Imaginal discs of Drosophila provide an excellent system with which to study morphogenesis, pattern formation and cell proliferation in an epithelium. Discs are sac-like in structure and are composed of two epithelial layers: an upper peripodial epithelium and lower disc proper. Although development of the disc proper has been studied extensively in terms of cell proliferation, cell signaling mechanisms and pattern formation, little is known about these same processes in the peripodial epithelium. We address this topic by focusing on morphogenesis, compartmental organization, proliferation and cell lineage of the PE in wing, second thoracic leg (T2) and eye discs. We show that a subset of peripodial cells in different imaginal discs undergo a cuboidal-to-squamous cell shape change at distinct larval stages. We find that this shape change requires both Hedgehog and Decapentapelagic, but not Wingless, signaling. Additionally, squamous morphogenesis shifts the anteroposterior (AP) compartment boundary in the peripodial epithelium relative to the stationary AP boundary in the disc proper. Finally, by lineage tracing cells in the PE, we surprisingly find that peripodial cells are displaced into the disc proper during larval development and this movement leads to Ubx repression.     

In the footsteps of sea stars: deciphering the catalogue of proteins involved in underwater temporary adhesion

Sea stars adhere strongly but temporarily to underwater substrata via the secretion of a blend of proteins, forming an adhesive footprint that they leave on the surface after detachment. Their tube feet enclose a duo-gland adhesive system comprising two types of adhesive cells, contributing different layers of the footprint and de-adhesive cells. In this study, we characterized the catalogue of sea star footprint proteins (Sfps) in the species Asterias rubens to gain insights in their potential function. We identified 16 Sfps and mapped their expression to type 1 and/or type 2 adhesive cells or to de-adhesive cells by double fluorescent in situ hybridization. Based on their cellular expression pattern and their conserved functional domains, we propose that the identified Sfps serve different functions during attachment, with two Sfps coupling to the surface, six providing cohesive strength and the rest forming a binding matrix. Immunolabelling of footprints with antibodies directed against one protein of each category confirmed these roles. A de-adhesive gland cell-specific astacin-like proteinase presumably weakens the bond between the adhesive material and the tube foot surface during detachment. Overall, we provide a model for temporary adhesion in sea stars, including a comprehensive list of the proteins involved.     

Morphological features of the epididymal epithelium of gerbil, Meriones unguiculatus

Principal cells of the ducts epididymis of the Mongolian gerbil showed ultrastructural characteristics of lining epithelium cells close related to processes of protein secretion, and transcytosis occurring between adjacent principal cells which were mainly verified in the initial segment. Principal cells also presented roles of fluid phase and adsorptive endocytoses, as well as autophagic and heterophagic lysosomal activities mainly observed in the caput epididymis. Columnar (principal) cells of the corpus epididymidis presented great number of variable vesicles and vacuoles distributed in all the cytoplasmic levels occurring a progressive coalescence pattern among them, which help to guarantee formation of cytoplasmic channels for fluid phase transport between the tubular lumen and epididymal interstitium. Clear cells were presented in the initial segment and predominately in the cauda epididymis epithelium of the gerbil and showed marked ultrastructural characteristics of endocytosis activities occurrence, perhaps directly related to the turnover of fluid phase of spermatozoa stored into the lumen of the distal tail. Other epididymal epithelium cells were verified and described such as basal, halo, apical and dark cells, but they did not presented special ultrastructural features.     

Pili mediate specific adhesion of Streptococcus pyogenes to human tonsil and skin

Very little is known about the biological functions of pili that have recently been found to be expressed by important Gram-positive pathogens such as Corynebacterium diphtheriae, Streptococcus agalacticae, S. pneumoniae and S. pyogenes. Using various ex vivo tissue and cellular models, here we show that pili mediate adhesion of serotype M1 S. pyogenes strain SF370 to both human tonsil epithelium and primary human keratinocytes, which represent the two main sites of infection by this human-specific pathogen. Mutants lacking minor pilus subunits retained the ability to express cell-surface pili, but these were functionally defective. In contrast to above, pili were not required for S. pyogenes adhesion to either immortalized HEp-2 or A549 cells, highlighting an important limitation of these extensively used adhesion/invasion models. Adhering bacteria were internalized very effectively by both HEp-2 and A549 cells, but not by tonsil epithelium or primary keratinocytes. While pili acted as the primary adhesin, the surface M1 protein clearly enhanced adhesion to tonsil, but surprisingly, had the opposite effect on adhesion to keratinocytes. These studies provide clear evidence that S. pyogenes pili display an adhesive specificity for clinically relevant human tissues and are likely to play a critical role in the initial stages of infection.     

Enabled (Xena) regulates neural plate morphogenesis, apical constriction, and cellular adhesion required for neural tube closure in Xenopus

Regulation of cellular adhesion and cytoskeletal dynamics is essential for neurulation, though it remains unclear how these two processes are coordinated. Members of the Ena/VASP family of proteins are localized to sites of cellular adhesion and actin dynamics and lack of two family members, Mena and VASP, in mice results in failure of neural tube closure. The precise mechanism by which Ena/VASP proteins regulate this process, however, is not understood. In this report, we show that Xenopus Ena (Xena) is localized to apical adhesive junctions of neuroepithelial cells during neurulation and that Xena knockdown disrupts cell behaviors integral to neural tube closure. Changes in the shape of the neural plate as well as apical constriction within the neural plate are perturbed in Xena knockdown embryos. Additionally, we demonstrate that Xena is essential for cell-cell adhesion. These results demonstrate that Xena plays an integral role in coordinating the regulation of cytoskeletal dynamics and cellular adhesion during neurulation in Xenopus.     

sLeX/L-selectin mediates adhesion in vitro implantation model

The complex implantation process is initiated by the recognition and adhesion between the embryo and uterine endometrial epithelium. The expression and interactions between the adhesive molecules from both fetal and maternal sides are crucial for the successful implantation. In this study, we aimed to investigate the expression and adhesive function of sLeX on the trophoblasts and L-selectin on uterine epithelial cells mediated the adhesion at the fetal-maternal interface, and to further explore whether this adhesion system could induce endometrial apoptosis, using in vitro implantation model consisting of the human trophoblast cell line (JAR) and human uterine epithelial cell line (RL95-2). The results showed that sLeX was expressed on JAR cells by indirect immunofluorescence staining. After transfection of JAR cells with fucosyltransferase VII (FUT7) which is the key enzyme for sLeX synthesis, the expression of FUT7 and sLeX synthesis were increased, and the percent adhesion of trophoblast cells to RL95-2 cell monolayer was significantly increased (P?相似文献   

Platelet adhesion to fibrinogen-coated glass at an abrupt tubular expansion viewed with fluorescent video-microscopy

The adhesion and detachment of human washed platelets was studied on the surface of the larger tube of a tubular expansion. Measurements were made within the vortex, at the reattachment point and downstream of the vortex. Fluorescent video-microscopy of mepacrine labelled platelets was used to record data continuously. Flow was from the smaller to the larger tube at Reynolds numbers (based on upstream conditions) of 75.4 and 212.2. Measurements of the adhesion efficiency for initially contacting cells and an overall adhesion efficiency were made. These efficiencies decreased with increasing Reynolds number. There was a pattern of variability for both efficiencies with respect to position and Reynolds number which is consistent with the generation of the unstable flow at the reattachment point.     

The odd-skipped family of zinc finger genes promotes Drosophila leg segmentation

Notch signaling controls formation of joints at leg segment borders and growth of the developing Drosophila leg. Here, we identify the odd-skipped gene family as a key group of genes that function downstream of the Notch receptor to promote morphological changes associated with joint formation during leg development. odd, sob, drm, and bowl are expressed in a segmental pattern in the developing leg, and their expression is regulated by Notch signaling. Ectopic expression of odd, sob, or drm can induce invaginations in the leg disc epithelium and morphological changes in the adult leg that are characteristic of endogenous invaginating joint cells. These effects are not due to an alteration in the expression of other genes of the developing joint. While odd or drm mutant clones do not affect leg segmentation, and thus appear to act redundantly, bowl mutant clones do perturb leg development. Specifically, bowl mutant clones result in a failure of joint formation from the distal tibia to tarsal segment 5, while more proximal clones cause melanotic protrusions from the leg cuticle. Together, these results indicate that the odd-skipped family of genes mediates Notch function during leg development by promoting a specific aspect of joint formation, an epithelial invagination. As the odd-skipped family genes are involved in regulating cellular morphogenesis during both embryonic segmentation and hindgut development, we suggest that they may be required in multiple developmental contexts to induce epithelial cellular changes.