Neural cell adhesion molecule: structure, immunoglobulin-like domains, cell surface modulation, and alternative RNA splicing

The neural cell adhesion molecule, N-CAM, appears on early embryonic cells and is important in the formation of cell collectives and their boundaries at sites of morphogenesis. Later in development it is found on various differentiated tissues and is a major CAM mediating adhesion among neurons and between neurons and muscle. To provide a molecular basis for understanding N-CAM function, the complete amino acid sequences of the three major polypeptides of N-CAM and most of the noncoding sequences of their messenger RNA's were determined from the analysis of complementary DNA clones and were verified by amino acid sequences of selected CNBr fragments and proteolytic fragments. The extracellular region of each N-CAM polypeptide includes five contiguous segments that are homologous in sequence to each other and to members of the immunoglobulin superfamily, suggesting that interactions among immunoglobulin-like domains form the basis for N-CAM homophilic binding. Although different in their membrane-associated and cytoplasmic domains, the amino acid sequences of the three polypeptides appear to be identical throughout this extracellular region (682 amino acids) where the binding site is located. Variations in N-CAM activity thus do not occur by changes in the amino acid sequence that alter the specificity of binding. Instead, regulation is achieved by cell surface modulation events that alter N-CAM affinity, prevalence, mobility, and distribution on the surface. A major mechanism for modulation is alternative RNA splicing resulting in N-CAM's with different cytoplasmic domains that differentially interact with the cell membrane. Such regulatory mechanisms may link N-CAM binding function with other primary cellular processes during the embryonic development of pattern.     

SynCAM,a synaptic adhesion molecule that drives synapse assembly

Synapses, the junctions between nerve cells through which they communicate, are formed by the coordinated assembly and tight attachment of pre- and postsynaptic specializations. We now show that SynCAM is a brain-specific, immunoglobulin domain-containing protein that binds to intracellular PDZ-domain proteins and functions as a homophilic cell adhesion molecule at the synapse. Expression of the isolated cytoplasmic tail of SynCAM in neurons inhibited synapse assembly. Conversely, expression of full-length SynCAM in nonneuronal cells induced synapse formation by cocultured hippocampal neurons with normal release properties. Glutamatergic synaptic transmission was reconstituted in these nonneuronal cells by coexpressing glutamate receptors with SynCAM, which suggests that a single type of adhesion molecule and glutamate receptor are sufficient for a functional postsynaptic response.     

The neural cell adhesion molecule (NCAM) as a regulator of cell-cell interactions

The neural cell adhesion molecule (NCAM) can influence a number of diverse intercellular events, including junctional communication, the association of axons with pathways and targets, and signals that alter levels of neurotransmitter enzymes. These pleiotropic effects appear to reflect the ability of NCAM to regulate membrane-membrane contact required to initiate specific interactions between other molecules. Such regulation can occur through changes in either NCAM expression or the molecule's content of polysialic acid (PSA). When NCAM with a low PSA content is expressed, adhesion is increased and contact-dependent events are triggered. In contrast, the large excluded volume of NCAM PSA can inhibit cell-cell interactions through hindrance of overall membrane apposition.     

Endothelial expression of a mononuclear leukocyte adhesion molecule during atherogenesis

An inducible rabbit endothelial adhesion molecule that is selective for mononuclear leukocytes has been identified. This adhesion protein was expressed on the surface of activated cultured endothelium in two forms, 118 and 98 kilodaltons, the amino-terminal sequence of each being highly homologous to human VCAM-1. In dietary hypercholesterolemic and Watanabe heritable hyperlipidemic rabbit models of atherosclerosis, this adhesion molecule was found to be expressed in a localized fashion by aortic endothelium that overlies early foam cell lesions. This lesion-localized expression suggests a potential endothelium-dependent mechanism for mononuclear leukocyte recruitment during atherogenesis and may provide a molecular marker for early atherosclerosis.     

麦冬遗传多样性的RAPD分析及分子指纹图谱构建

以福建莆田、泉州、福安等地及浙江崇寿、湖北襄樊、四川三台等地34个自然居群的麦冬类植物为试材,以80 条 10 碱基随机引物进行RAPD 分析,研究百合科植物麦冬及山麦冬不同自然居群间的遗传多样性。试验筛选出15条有效引物,共扩增获得 1566条DNA多态性带,通过聚类分析,构建DNA 分子系统树图,确定了其居群及种间亲缘关系。结果表明,不同自然种群间麦冬类植物遗传差异明显,具有丰富的遗传多样性,其中野生资源比栽培类型遗传多样性更大;不同自然居群间遗传差异与地理分布联系并不紧密,而与形态差异联系较密切。     

Cadherin cell adhesion receptors as a morphogenetic regulator

Cadherins are a family of cell adhesion receptors that are crucial for the mutual association of vertebrate cells. Through their homophilic binding interactions, cadherins play a role in cell-sorting mechanisms, conferring adhesion specificities on cells. The regulated expression of cadherins also controls cell polarity and tissue morphology. Cadherins are thus considered to be important regulators of morphogenesis. Moreover, pathological examinations suggest that the down-regulation of cadherin expression is associated with the invasiveness of tumor cells.     

血清可溶性细胞间粘附分子在大肠癌患者组织中的检测及其意义

目的:探讨血清可溶性细胞间粘附分子1(sICAM-1)的检测在大肠癌患者中的临床意义。方法:采用双抗体夹心ELISA法检测50例大肠癌、30例大肠良性病变及30例健康体检者血清sICAM-1水平,并比较大肠癌患者术前、术后,转移、无转移sICAM-1水平变化。结果:大肠癌患者血清sICAM-1水平明显高于良性病变患者及正常人(P<0.01);大肠癌患者术后血清sICAM-1水平较术前明显下降(P<0.01);有转移的大肠癌患者血清sICAM-1水平高于无转移的患者(P<0.01)。结论:血清sICAM-1水平与大肠癌的发生、发展密切相关,可作为大肠癌新的检测指标之一。     

Lactate dehydrogenase: An important molecule involved in acetamizuril action against Eimeria tenella

Lactate dehydrogenase(LDH), a vital enzyme in anaerobic glycolysis, is closely associated with the survival of parasites. Previous studies of some parasites have shown that LDH exhibits unique physicochemical properties and molecular structures and may be an ideal potential target for diagnosis and drug screening. In this study, we aimed to investigate the effects of acetamizuril, a novel anticoccidial compound, on LDH in the second-generation merozoites of Eimeria tenella(mz-LDH). Quantitative real-time PCR, Western blot, immunofluorescence and enzyme activity assays were each applied to detect the changes of mz-LDH. Our results indicated that the mRNA and protein levels of mz-LDH were reduced upon acetamizuril treatment. Immunolocalization of mz-LDH demonstrated that considerable amount of mz-LDH was distributed around or in the nuclei of second-generation merozoites within the untreated group; in contrast, the acetamizuril-treated group had very low level of mz-LDH. Meanwhile, LDH enzyme activity assay suggested that a decreased LDH enzyme activity in both cytoplasm and nucleus of merozoites in the acetamizuril-treated group. Moreover, the induced apoptosis in second-generation merozoites by the acetamizuril was evaluated by detecting caspase 3 activity, and acetamizuril was found to significantly increase caspase 3 activity. The above findings show that LDH may play an important role in the mediating the activity of acetamizuril against coccidiosis, and further investigation into this aspect might contribute to new light on the pathogenesis of E. tenella during its interaction with acetamizuril.     

Molecular mechanisms and forces involved in the adhesion and fusion of amphiphilic bilayers

The surface forces apparatus technique was used for measuring the adhesion, deformation, and fusion of bilayers supported on mica surfaces in aqueous solutions. The most important force leading to the direct fusion of bilayers is the hydrophobic interaction, although the occurrence of fusion is not simply related to the force law between bilayers. Bilayers do not need to "overcome" some repulsive force barrier, such as hydration, before they can fuse. Instead, once bilayer surfaces come within about 1 nanometer of each other, local deformations and molecular rearrangements allow them to "bypass" these forces.     

Forces and bond dynamics in cell adhesion

Adhesion of a biological cell to another cell or the extracellular matrix involves complex couplings between cell biochemistry, structural mechanics, and surface bonding. The interactions are dynamic and act through association and dissociation of bonds between very large molecules at rates that change considerably under stress. Combining molecular cell biology with single-molecule force spectroscopy provides a powerful tool for exploring the complexity of cell adhesion, that is, how cell signaling processes strengthen adhesion bonds and how forces applied to cell-surface bonds act on intracellular sites to catalyze chemical processes or switch molecular interactions on and off. Probing adhesion receptors on strategically engineered cells with force during functional stimulation can reveal key nodes of communication between the mechanical and chemical circuitry of a cell.     

Sequential establishment of stripe patterns in an expanding cell population

Periodic stripe patterns are ubiquitous in living organisms, yet the underlying developmental processes are complex and difficult to disentangle. We describe a synthetic genetic circuit that couples cell density and motility. This system enabled programmed Escherichia coli cells to form periodic stripes of high and low cell densities sequentially and autonomously. Theoretical and experimental analyses reveal that the spatial structure arises from a recurrent aggregation process at the front of the continuously expanding cell population. The number of stripes formed could be tuned by modulating the basal expression of a single gene. The results establish motility control as a simple route to establishing recurrent structures without requiring an extrinsic pacemaker.     

Evidence of a pluripotent human embryonic stem cell line derived from a cloned blastocyst

Somatic cell nuclear transfer (SCNT) technology has recently been used to generate animals with a common genetic composition. In this study, we report the derivation of a pluripotent embryonic stem (ES) cell line (SCNT-hES-1) from a cloned human blastocyst. The SCNT-hES-1 cells displayed typical ES cell morphology and cell surface markers and were capable of differentiating into embryoid bodies in vitro and of forming teratomas in vivo containing cell derivatives from all three embryonic germ layers in severe combined immunodeficient mice. After continuous proliferation for more than 70 passages, SCNT-hES-1 cells maintained normal karyotypes and were genetically identical to the somatic nuclear donor cells. Although we cannot completely exclude the possibility that the cells had a parthenogenetic origin, imprinting analyses support a SCNT origin of the derived human ES cells.     

水稻、玉米胚性悬浮细胞系的有效建立

研究了水稻、玉米胚性悬浮细胞系有效建立的几个关键性技术问题。指出外植体是影响初代愈伤组织状态的因素之一，提出了愈伤组织继代改造的一些措施、影响胚性悬浮细胞系建立的几个因素和判别某材料能否建成胚性悬浮细胞系的参考标准。     

Inheritance of a cardiac arterial asymmetry in mice

A pair of coronary arteries supplies the interventricular septum of the heart of Mus musculus. The members of this pair tend to be of unequal size, which permits distiniction between specimens displaying left asymmetry and those showing righit asymmetry. Three inbred strains (C57BL/1O, DBA/1, and Bulb/c) differ with regard to this asymmetry. However, variation exists within strains, which suggests that nongenetic factors also influence the development of the asymmetry. Right arterial asymmetry is dominant over left asymmetry.     

Development of excitability in embryonic muscle cell membranes in certain tunicates

During the course of development of muscle cells in certain tunicates, a sign of regenerative membrane response appears in the gastrula stage. In the early tadpole larva, the action potential consists of a spike followed by a plateau. The latter-disappears in fully differentiated cells, conceivably in association with the establishment of delayed rectification.     

Capture of a single molecule in a nanocavity

We describe a heptameric protein pore that has been engineered to accommodate two different cyclodextrin adapters simultaneously within the lumen of a transmembrane beta barrel. The volume between the adapters is a cavity of approximately 4400 cubic angstroms. Analysis of single-channel recordings reveals that individual charged organic molecules can be pulled into the cavity by an electrical potential. Once trapped, an organic molecule shuttles back and forth between the adapters for hundreds of milliseconds. Such self-assembling nanostructures are of interest for the fabrication of multianalyte sensors and could provide a means to control chemical reactions.     

Hyaluronic acid: a novel, double helical molecule

Films prepared from a deformable gel (or putty) of hyaluronic acid show high crystallinity and orientation in their x-ray diffraction patterns. We have derived a probable structure for the molecules in these films. This is a double helix in which two identical, left-handed strands are antiparallel to one another. Each strand has four disaccharide residues per pitch length. Although the putty is prepared at pH 2.5, at which dilute solutions of hyaluronic have exaggerated rheological properties, the double helical form can also exist at physiological pH and therefore may be a biologically important form.     

New perspectives in cell adhesion: RGD and integrins

Rapid progress has been made in the understanding of the molecular interactions that result in cell adhesion. Many adhesive proteins present in extracellular matrices and in the blood contain the tripeptide arginine-glycine-aspartic acid (RGD) as their cell recognition site. These proteins include fibronectin, vitronectin, osteopontin, collagens, thrombospondin, fibrinogen, and von Willebrand factor. The RGD sequences of each of the adhesive proteins are recognized by at least one member of a family of structurally related receptors, integrins, which are heterodimeric proteins with two membrane-spanning subunits. Some of these receptors bind to the RGD sequence of a single adhesion protein only, whereas others recognize groups of them. The conformation of the RGD sequence in the individual proteins may be critical to this recognition specificity. On the cytoplasmic side of the plasma membrane, the receptors connect the extracellular matrix to the cytoskeleton. More than ten proved or suspected RGD-containing adhesion-promoting proteins have already been identified, and the integrin family includes at least as many receptors recognizing these proteins. Together, the adhesion proteins and their receptors constitute a versatile recognition system providing cells with anchorage, traction for migration, and signals for polarity, position, differentiation, and possibly growth.     

Selective inhibition of fibronectin-mediated cell adhesion by monoclonal antibodies to a cell-surface glycoprotein

Fibroblasts possess several distinct mechanisms that control cellular adhesion to extracellular matrix macromolecules. Monoclonal antibodies to a 140-kilodalton (kD) cell surface glycoprotein inhibited the adhesion of fibroblastic Chinese hamster ovary cells to fibronectin-coated substrata but did not inhibit adhesion to substrata coated with vitronectin, laminin, serum, or other adhesive macromolecules. Thus the 140-kD glycoprotein appears to be involved in the fibronectin-mediated adhesion mechanism but not in other adhesion processes.