http://kbose.weebly.com/uploads/1/0/4/9/10492046/force-distance_curves_by_atomic_force_microscopy_1.pdf

Force-distance curves by atomic force microscopy

Because of its piconewton force sensitivity and nanometer positional accuracy, the atomic force microscope (AFM) has emerged as a powerful tool for exploring the forces and the dynamics of the interaction between individual ligands and receptors, either on isolated molecules or on cellular surfaces. These studies require attaching specific biomolecules or cells on AFM tips and on solid supports and measuring the unbinding forces between the modified surfaces using AFM force spectroscopy. In this review, we describe the current methodology for molecular recognition studies using the AFM, with an emphasis on strategies available for preparing AFM tips and samples, and on procedures for detecting and localizing single molecular recognition events.

https://www.rug.nl/research/biomaterials/publications/presentations/hjb4/hinterdorfer-nature_methods_2006.pdf

Detection and localization of single molecular recognition events using atomic force microscopy

1. Introduction to the cell Part I. Rods and Ropes: 2. Polymers 3. Two-dimensional networks 4. Three-dimensional networks Part II. Membranes: 5. Biomembranes 6. Membrane undulations Part III. The Whole Cell: 7. The simplest cells 8. Intermembrane forces 9. Dynamic filaments 10. Mechanical designs Appendix A. Animal cells and tissues Appendix B. The cell's molecular building blocks Appendix C. Elementary statistical mechanics Appendix D. Elasticity References Index.

/pdf/mechanics-of-the-cell-5g5c71kjw2.pdf

Mechanics of the cell

A method for locating a chemical substance on the surface of a material and for determining the contour of a surface of a material using a scanning electrochemical microscope is provided in the present invention. The substance to be examined is immersed in a solution, the tip of a working electrode is positioned in the solution proximate the surface and an electric potential is connected directly or indirectly between the tip and the material generating a current through the tip and producing an electrochemical reaction. The current through the tip is measured at a plurality of points while the tip is scanned across the surface. The current at each point in the scan is preferably plotted to produce an image of the contour or of the differing chemical compositions on the surface of the substance being examined. The solution in which the substance and working electrode tip are immersed is chosen to enable electrochemically generated reduction and oxidation processes to occur between the surface and the tip. The changing contour or change of chemical substances over which the working electrode is scanned produces related differences in current through the tip. Light emission by electrogenerated chemiluminescence or inverse photoemission spectroscopy may also be produced and measured in the method of the present invention.

Scanning electrochemical microscopy

Tube and lumen formation are essential steps in forming a functional vasculature. Despite their significance, our understanding of these processes remains limited, especially at the cellular and molecular levels. In this study, we analyze mechanisms of angioblast coalescence in the zebrafish embryonic midline and subsequent vascular tube formation. To facilitate these studies, we generated a transgenic line where EGFP expression is controlled by the zebrafish flk1 promoter. We find that angioblasts migrate as individual cells to form a vascular cord at the midline. This transient structure is stabilized by endothelial cell-cell junctions, and subsequently undergoes lumen formation to form a fully patent vessel. Downregulating the VEGF signaling pathway, while affecting the number of angioblasts, does not appear to affect their migratory behavior. Our studies also indicate that the endoderm, a tissue previously implicated in vascular development, provides a substratum for endothelial cell migration and is involved in regulating the timing of this process, but that it is not essential for the direction of migration. In addition, the endothelial cells in endodermless embryos form properly lumenized vessels, contrary to what has been previously reported in Xenopus and avian embryos. These studies provide the tools and a cellular framework for the investigation of mutations affecting vasculogenesis in zebrafish.

/pdf/cellular-and-molecular-analyses-of-vascular-tube-and-lumen-aijjtyws6q.pdf

Cellular and molecular analyses of vascular tube and lumen formation in zebrafish

Measurement of binding forces intrinsic to adhesion molecules is necessary to assess their contribution to the maintenance of the anatomical integrity of multicellular organisms. Atomic force microscopy was used to measure the binding strength between cell adhesion proteoglycans from a marine sponge. Under physiological conditions, the adhesive force between two cell adhesion molecules was found to be up to 400 piconewtons. Thus a single pair of molecules could hold the weight of 1600 cells. High intermolecular binding forces are likely to form the basis for the integrity of the multicellular sponge organism.

/pdf/binding-strength-between-cell-adhesion-proteoglycans-31fvm3czn2.pdf

Binding Strength Between Cell Adhesion Proteoglycans Measured by Atomic Force Microscopy

Carbohydrate-carbohydrate interactions of a novel acidic glycan can mediate sponge cell adhesion.

Involvement of carbohydrates as multiple low affinity interaction sites in the self-association of the aggregation factor from the marine sponge Microciona prolifera.

Characterization of a novel pyruvylated carbohydrate unit implicated in the cell aggregation of the marine sponge Microciona prolifera.

To explore direct effects of platelet-derived growth factor (PDGF) on endothelial cells during angiogenesis in vitro, we have used cloned bovine aortic endothelial cells that spontaneously form cord structures. Recently we have shown that cells forming these endothelial cords express PDGF beta-receptors and that PDGF-BB can contribute to cellular proliferation and cord formation. In this study we investigated whether PDGF-induced cellular migration might also contribute to endothelial repair and angiogenesis in vitro. Ten individual endothelial cells in cords were tracked at an early stage of cord formation by video-timelapse microscopy. PDGF-BB (100 ng/ml) induced an increase in endothelial cell movement of 67 +/- 15% as compared with diluent control. Interestingly, PDGF-BB also increased movements of entire cord structures, followed at branching points, by 53 +/- 12% over diluent control. Taken together, these video-timelapse experiments suggested that the apparent movements of single endothelial cord cells might also be due to the motion of entire underlying cord structures in response to PDGF. To analyze the response of single endothelial cord cells we therefore examined whether PDGF-induced migration contributes to endothelial repair. Abrasions were applied with a razor blade to confluent monolayers of endothelial cells at an intermediate stage of cord formation. PDGF-BB concentration-dependently increased the distance to which cord-forming endothelial cells migrated into the abrasion. An increased number of elongated, i.e., probably migrating, endothelial cells was found in the abrasion in response to PDGF-BB. However, there was no effect of PDGF-BB on the total number of endothelial cells found in the abrasion. PDGF-AA affected neither the distance to which the cells migrated nor the number of elongated cells. Actin and tubulin stainings revealed that these cytoskeletal structures were not appreciably altered by PDGF-BB. Furthermore, urokinase-type plasminogen activator transcripts were not modulated in response to PDGF-BB. We conclude that in this model of angiogenesis in vitro PDGF-BB can elicit the movement of entire cord structures, possibly via u-PA-independent mechanisms. PDGF-BB also controls the migration of single cord-forming endothelial cells. Thus, PDGF-BB possibly contributes to endothelial repair and angiogenesis by direct effects on proliferation and composite movements of PDGF beta-receptor-expressing endothelial cells and cords.

Gradimir N. Misevic

Papers

Binding Strength Between Cell Adhesion Proteoglycans Measured by Atomic Force Microscopy

Carbohydrate-carbohydrate interactions of a novel acidic glycan can mediate sponge cell adhesion.

Involvement of carbohydrates as multiple low affinity interaction sites in the self-association of the aggregation factor from the marine sponge Microciona prolifera.

Characterization of a novel pyruvylated carbohydrate unit implicated in the cell aggregation of the marine sponge Microciona prolifera.

PDGF‐BB increases endothelial migration and cord movements during angiogenesis in vitro