作者感谢安娜 Labernadie, 纪尧姆 Charrière 和帕特里克 Delobelle 为这项工作的最初贡献, 并马修桑切斯和弗朗索瓦斯·汉普森 Viala 为他们的帮助, 视频拍摄和编辑。这项工作得到了研究所 (ANR14-CE11-0020-02)、la 基金会研究所 Médicale (FRM DEQ2016 0334894)、INSERM 计划癌症、图卢兹癌症和人类前沿科学计划 (RGP0035/2016) 的支持。

1. Formvar 涂层网格的制备
<ol><li>清洁电子显微镜网格与纯丙酮和干燥他们在滤纸上。然后用纯乙醇清洁显微镜滑梯, 用透镜纸擦拭, 用鼓风机清除灰尘。</li>
	<li>将乙醇清洗过的玻璃垂直放在薄膜浇铸装置的漏斗上, 其中含有下部 Formvar 的溶液。覆盖漏斗顶部。</li>
	<li>将100毫升的 Formvar 溶液 (二氯化乙烯中的 0.5%) 与雾化灯泡泵浦, 直到水平达到滑动的两个以上。</li>
	<li>在解决方案中保留幻灯片1分钟。</li>
	<li>打开设备的阀门以在稳定的流中排出 Formvar 溶液。流速为10至15毫升/秒将产生一个 Formvar 膜 30-80 nm。薄膜的厚度是由 Formvar 溶液的浓度和排水速率决定的。 注: 通过将阀门慢慢打开, 通过排气阀排出压力, 可以控制排水速率。排水越快, 胶片越厚。在实践中, 由于难以预测薄膜厚度从 Formvar 流速, 我们准备了几批 Formvar 薄膜和控制其厚度的 AFM (见步骤 2)。</li>
	<li>从腔室取出滑块, 并在滤纸上微妙地晾干, 以除去任何液体 Formvar。</li>
	<li>用剃刀刀片从 Formvar 胶片上剪下一个20毫米 x 50 毫米的长方形。</li>
	<li>用干净的蒸馏水填满烧杯, 慢慢地将幻灯片垂直地浸入水中漂浮在胶片上: 胶片应该漂浮在水面上。</li>
	<li>将干丙酮清洗的网格放在胶片上, 面朝上发亮。</li>
	<li>将圆形玻璃盖玻片 (直径12毫米) 放到几个网格上。此盖玻片将用于测量胶片厚度 (见步骤 2)。</li>
	<li>覆盖一个显微镜幻灯片与一个白色的标签调整大小, 以适应它。将幻灯片垂直倾斜在浮动 Formvar 胶片的边框上, 直到整个胶片粘附在幻灯片上。用滤纸把多余的水从滑梯上取出, 让它在室温下一夜之间晾干。</li>
</ol>2. 薄膜厚度的测量
<ol><li>用镊子把盖玻片周围的 Formvar, 从滑梯上分离出来。</li>
	<li>用钢笔在盖玻片下标记网格的位置。</li>
	<li>在标记的网格周围剪切 Formvar, 将其与盖玻片分离。因此, 在剩余的 Formvar 板上会有一个洞, 这将允许测量胶片的厚度。用 PBS 覆盖盖玻片, 并将其放在显微镜上的玻璃滑梯上。</li>
	<li>在 AFM 玻璃块上安装氮化硅悬臂, 确保金色条纹不被弹簧的尖端覆盖。 注意: 悬臂的灵敏度和弹簧常数应该以前在 PBS 中校准过。</li>
	<li>将玻璃块安装到 AFM 模块上, 然后将该模块放到显微镜上。</li>
	<li>将 Formvar 涂层的盖玻片放在观察室上, 并盖上500µL PBS。</li>
	<li>用 AFM 在接触模式和 0.5 nN 力设定点扫描 Formvar 板孔的边界。</li>
	<li>使用玻璃盖玻片表面作为高度测量的参考, 并评估 Formvar 厚度为剖面的高度 (每 Formvar 批次至少执行10次测量)。</li>
</ol>3. 在网格上播种细胞
<ol><li>在无菌罩下, 在盖玻片上放置一个带 (12 毫米 x 3 毫米) 的双面胶带。</li>
	<li>用镊子剪掉一个 Formvar 的网格, 把它倒在胶条上 (只有网格的边缘需要附着在胶带上)。Formvar 电影需要面对盖玻片。</li>
	<li>把这个设备放在一个文化中。</li>
	<li>放置一个10µL 滴 RPMI 没有 FCS 含有 104巨噬细胞分化为人单核细胞16。 注意: 确保不要用吸管尖接触网格, 以防止损坏 Formvar 涂层。</li>
	<li>孵育30分钟 (37 °c, 5% CO2) 让细胞坚持。</li>
	<li>用2毫升的含10% 的 RPMI 填充井。</li>
	<li>在37摄氏度和 5% CO2上孵化设备2小时, 让细胞在 AFM 观察之前坚持。</li>
</ol>4. Podosome 诱发变形的地形测量
<ol><li>将两条双面胶带贴在玻璃底培养皿上。 注: 两条线之间的距离应小于网格直径。</li>
	<li>小心地从胶带上分离出与巨噬细胞电镀的格子。</li>
	<li>将网格倒置, 使单元格面对玻璃, 并将栅格粘在两条粘合带之间。</li>
	<li>固定网格与两个新的双面胶条: 网格将因此被夹在两个胶条之间, 使网格的中心区域可进入 AFM 尖端。 注意: 确保网格是固定的, 而不是扭曲的;否则, AFM 悬臂可能无法接近 Formvar 表面。</li>
	<li>用2毫升预加热的37°c 培养基 (RPMI 和 10% FCS) 填充培养皿, 辅以10毫米 HEPES (pH 7.4)。</li>
	<li>将养殖盘放在37摄氏度的盘子加热器上。</li>
	<li>在 AFM 阶段安装碟式加热器。</li>
	<li>让系统稳定在37摄氏度。</li>
	<li>在接触模式与 0.5 nN 力量, 使第一个全局图像定位 podosomes, 然后扫描 Formvar 地形在3赫兹与大约 20 nm 大像素。 注意: 避免在网格边缘附近进行扫描。</li>
</ol>

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没有宣布利益冲突。

材料性能
可变形膜材料的选择, 在我们的案例中 Formvar, 需要满足一些要求。该材料必须是透明的可见光和展示有限的自动荧光, 以允许观察在明亮的领域和荧光显微镜。薄膜的粗糙度必须低于10纳米, 以避免任何地形对细胞黏附的影响, 并允许通过 AFM 成像清晰地观察细胞诱发的突起。最后, 根据杨氏模量和材料厚度的不同, 膜的刚度需要足够高, 以诱导 podosomes 的形...

动物细胞与基质和构成其环境的其他细胞在物理上相互作用1。这是需要他们迁移, 内化机构, 获取外部信息, 或区分。在这种过程中, 细胞必须产生机械力, 正如近年来许多研究表明的那样, 细胞产生力量和探测其环境的能力会影响其生物学行为, 例如扩散或分化2,3。反过来, 细胞力的测量是研究力量生成规律的主要辅助因素, 并了解它在细胞行为和组织命运4,5中的意义。
最近几年目睹了许多技术的发展, 以测量细胞在其环境中所能发挥的力量6。大多数这些都有助于揭示细胞在移动探针或变形基板上施加的牵引力。然而, 在细胞外环境中所涉及的机械力缺乏测量技术, 至今尚无良好的特征。
为了克服这一限制, 我们提出了一种测量施加正交到基体上的力的方法。它包括在一个薄的弹性薄板上的电镀活细胞, 可以在正交方向上变形, 使其能够测量基底变形的细胞和推断所涉及的力量。用原子力显微镜测量基片的形貌, 用纳米尺度的分辨率测定, 变形力的评估依赖于突出细胞结构的几何知识7,8,9。
在这里, 我们描述的设置和它的应用, 以测量 podosomes 产生的力量, 突出黏附结构形成的巨噬细胞为他们的间充质迁移在三维环境10,11, 12,13,14,15,16,17。我们相信, 这一技术将促进理解的力量产生和它的调节, 在许多细胞过程涉及突出。

<table><tbody><tr><td>200 mesh nickel grids</td><td>Electron Microscopy Sciences</td><td>G200-Ni</td><td></td></tr><tr><td>Filter paper</td><td>Sigma-Aldrich</td><td>1001-055</td><td></td></tr><tr><td>Microscope slides</td><td>Fisher Scientific</td><td>10235612</td><td></td></tr><tr><td>White stickers 26 x 70 mm</td><td>Avery</td><td>DP033-100</td><td></td></tr><tr><td>Film casting device with valve in its outlet</td><td>Electron Microscopy Sciences</td><td>71305-01</td><td></td></tr><tr><td>Razorblades</td><td>Electron Microscopy Sciences</td><td>72000</td><td></td></tr><tr><td>Ethanol</td><td>VWR</td><td>1.08543.0250</td><td></td></tr><tr><td>Acetone</td><td>VWR</td><td>20066.321</td><td></td></tr><tr><td>Formvar 0.5% solution in ethylene dichloride</td><td>Electron Microscopy Sciences</td><td>15820</td><td></td></tr><tr><td>12 mm coverslips</td><td>VWR</td><td>631-0666</td><td></td></tr><tr><td>Inverted microscope</td><td>Carl Zeiss</td><td>Axiovert 200</td><td></td></tr><tr><td>Atomic Force Microscope</td><td>JPK Instruments</td><td>NanoWizard III</td><td></td></tr><tr><td>Temperature-controlled sample holder&amp;nbsp;</td><td>JPK Instruments</td><td>BioCell</td><td></td></tr><tr><td>Silicon nitride cantilever with a nominal spring constant of 0.01 N/m</td><td>Veeco Instruments</td><td>MLCT-AUHW</td><td></td></tr><tr><td>PBS</td><td>Gibco</td><td>14190-094</td><td></td></tr><tr><td>Double-sided adhesive tape</td><td>APLI AGIPA</td><td>118100</td><td></td></tr><tr><td>RPMI 1640</td><td>Gibco</td><td>31870-025</td><td></td></tr><tr><td>FCS</td><td>Sigma-Aldrich</td><td>F7524</td><td></td></tr><tr><td>HEPES&amp;nbsp;</td><td>Sigma-Aldrich</td><td>H0887</td><td></td></tr><tr><td>35 mm glass-bottom Petri dishes</td><td>WPI</td><td>FD35-100</td><td></td></tr></tbody></table>

protrusion force microscopy: a method to quantify forces developed by cell protrusions

在许多生物学环境中, 动物细胞需要通过培养机械力来与环境相互作用。其中, 牵引力具有良好的特征, 但缺乏技术允许测量正交细胞所施加的凸出力。我们设计了一个实验装置来测量附着细胞在基板上施加的凸出力。在兼容的 Formvar 板上镀的细胞变形了这种基底, 由此产生的地形被原子力显微镜 (AFM) 在纳米尺度上映射。然后从基于突出细胞结构几何的变形剖面分析中提取力值。因此, 一个活细胞的个别凸出单位施加的作用力可以随着时间的推移而测量。这一技术将使研究的力量产生和它的调节, 在许多细胞过程涉及突出。在这里, 我们描述了它的应用, 以测量由人巨噬细胞形成的 podosomes 产生的突出力。

上述协议描述了如何准备实验设置, 以量化在 Formvar 基板上应用巨噬细胞 podosomes 的突力。这是使用 AFM 实现的, 如图 1所示。
利用 JPK 数据处理软件对 podosomes 下凸起的地形图像进行分析时, 应独立地从每条扫描线中减去三度多项式拟合。可以通过在图像侧面添加 z 色刻度来评估 podosome 引起的颠簸的最大高...

Watch this Scientific Journal Video about Protrusion Force Microscopy: A Method to Quantify Forces Developed by Cell Protrusions at JoVE.com

Protrusion Force Microscopy: A Method to Quantify Forces Developed by Cell Protrusions

在这里, 我们详细介绍了用于评估 podosomes 在兼容薄膜上应用的突出力的实验技术, 从薄膜的制备到地形图像的自动分析。

凸出力显微镜: 一种量化细胞突起力的方法

In numerous biological contexts, animal cells need to interact physically with their environment by developing mechanical forces. Among these, traction ...

protrusion-force-microscopy-method-to-quantify-forces-developed-cell

Research

JoVE Journal

Biology

5.5K 次观看.  IPBS, Université de Toulouse, CNRS, UPS. 在这里, 我们详细介绍了用于评估 podosomes 在兼容薄膜上应用的突出力的实验技术, 从薄膜的制备到地形图像的自动分析。

视频: Protrusion Force Microscopy: A Method to Quantify Forces Developed by Cell Protrusions

A Direct Force Probe for Measuring Mechanical Integration Between the Nucleus and the Cytoskeleton

The mechanical properties of the nucleus determine its response to mechanical forces generated in cells. Because the nucleus is molecularly continuous with the cytoskeleton, methods are needed to probe its mechanical behavior in adherent cells. Here, we discuss the direct force probe (DFP) as a tool to apply force directly to the nucleus in a living adherent cell. We attach a narrow micropipette to the nuclear surface with suction. The micropipette is translated away from the nucleus, which causes the nucleus to deform and translate. When the restoring force is equal to the suction force, the nucleus detaches and elastically relaxes. Because the suction pressure is precisely known, the force on the nuclear surface is known. This method has revealed that nano-scale forces are sufficient to deform and translate the nucleus in adherent cells, and identified cytoskeletal elements that enable the nucleus to resist forces. The DFP can be used to dissect the contributions of cellular and nuclear components to nuclear mechanical properties in living cells.

In this protocol, we describe a micropipette method to directly apply a controlled force to the nucleus in a living cell. This assay allows interrogation of nuclear mechanical properties in the living, adherent cell.

测量细胞核与骨架间机械一体化的直接力探针

The mechanical properties of the nucleus determine its response to mechanical forces generated in cells. Because the nucleus is molecularly continuous ...

科研

生物化学

Perturbing Endothelial Biomechanics via Connexin 43 Structural Disruption

Endothelial cells have been established to generate intercellular stresses and tractions, but the role gap junctions play in endothelial intercellular stress and traction generation is currently unknown. Therefore, we present here a mechanics-based protocol to probe the influence of gap junction connexin 43 (Cx43) has on endothelial biomechanics by exposing confluent endothelial monolayers to a known Cx43 inhibitor 2,5-dihydroxychalcone (chalcone) and measuring the impact this inhibitor has on tractions and intercellular stresses. We present representative results, which show a decrease in both tractions and intercellular stresses under a high chalcone dosage (2 &#181;g/mL) when compared to control. This protocol can be applied to not just Cx43, but also other gap junctions as well, assuming the appropriate inhibitor is used. We believe this protocol will be useful in the fields of cardiovascular and mechanobiology research.

Here, we present a mechanics-based protocol to disrupt the gap junction connexin 43 and measure the subsequent impact this has on endothelial biomechanics via observation of tractions and intercellular stresses.

通过 Connexin 43 结构中断干扰内皮生物力学

Endothelial cells have been established to generate intercellular stresses and tractions, but the role gap junctions play in endothelial intercellular ...

Fluorescence Biomembrane Force Probe: Concurrent Quantitation of Receptor-ligand Kinetics and Binding-induced Intracellular Signaling on a Single Cell

Membrane receptor-ligand interactions mediate many cellular functions. Binding kinetics and downstream signaling triggered by these molecular interactions are likely affected by the mechanical environment in which binding and signaling take place. A recent study demonstrated that mechanical force can regulate antigen recognition by and triggering of the T-cell receptor (TCR). This was made possible by a new technology we developed and termed fluorescence biomembrane force probe (fBFP), which combines single-molecule force spectroscopy with fluorescence microscopy. Using an ultra-soft human red blood cell as the sensitive force sensor, a high-speed camera and real-time imaging tracking techniques, the fBFP is of ~1 pN (10-12 N), ~3 nm and ~0.5 msec in force, spatial and temporal resolution. With the fBFP, one can precisely measure single receptor-ligand binding kinetics under force regulation and simultaneously image binding-triggered intracellular calcium signaling on a single live cell. This new technology can be used to study other membrane receptor-ligand interaction and signaling in other cells under mechanical regulation.

We describe a technique for concurrently measuring force-regulated single receptor-ligand binding kinetics and real-time imaging of calcium signaling in a single T lymphocyte.

生物膜荧光探针力:受体 - 配体动力学并行和定量结合诱导细胞内信号作用于单细胞

Membrane receptor-ligand interactions mediate many cellular functions. Binding kinetics and downstream signaling triggered by these molecular interactions ...

生物工程

Probing Cell Mechanics with Bead-Free Optical Tweezers in the Drosophila Embryo

Morphogenesis requires coordination between genetic patterning and mechanical forces to robustly shape the cells and tissues. Hence, a challenge to understand morphogenetic processes is to directly measure cellular forces and mechanical properties in vivo during embryogenesis. Here, we present a setup of optical tweezers coupled to a light sheet microscope, which allows to directly apply forces on cell-cell contacts of the early Drosophila embryo, while imaging at a speed of several frames per second. This technique has the advantage that it does not require the injection of beads into the embryo, usually used as intermediate probes on which optical forces are exerted. We detail step by step the implementation of the setup, and propose tools to extract mechanical information from the experiments. By monitoring the displacements of cell-cell contacts in real time, one can perform tension measurements and investigate cell contacts&#39; rheology.

Probing Cell Mechanics with Bead-Free Optical Tweezers in the Drosophila Embryo

We present a setup of optical tweezers coupled to a light sheet microscope, and its implementation to probe cell mechanics without beads in the Drosophila embryo.

无珠光高音喇叭在食子胚胎中的细胞力学探测

Morphogenesis requires coordination between genetic patterning and mechanical forces to robustly shape the cells and tissues. Hence, a challenge to ...

发育生物学

Direct Force Measurements of Subcellular Mechanics in Confinement using Optical Tweezers

During the development of a multicellular organism, a single fertilized cell divides and gives rise to multiple tissues with diverse functions. Tissue morphogenesis goes in hand with molecular and structural changes at the single cell level that result in variations of subcellular mechanical properties. As a consequence, even within the same cell, different organelles and compartments resist differently to mechanical stresses; and mechanotransduction pathways can actively regulate their mechanical properties. The ability of a cell to adapt to the microenvironment of the tissue niche thus is in part due to the ability to sense and respond to mechanical stresses. We recently proposed a new mechanosensation paradigm in which nuclear deformation and positioning enables a cell to gauge the physical 3D environment and endows the cell with a sense of proprioception to decode changes in cell shape. In this article, we describe a new method to measure the forces and material properties that shape the cell nucleus inside living cells, exemplified on adherent cells and mechanically confined cells. The measurements can be performed non-invasively with optical traps inside cells, and the forces are directly accessible through calibration-free detection of light momentum. This allows measuring the mechanics of the nucleus independently from cell surface deformations and allowing dissection of exteroceptive and interoceptive mechanotransduction pathways. Importantly, the trapping experiment can be combined with optical microscopy to investigate the cellular response and subcellular dynamics using fluorescence imaging of the cytoskeleton, calcium ions, or nuclear morphology. The presented method is straightforward to apply, compatible with commercial solutions for force measurements, and can easily be extended to investigate the mechanics of other subcellular compartments, e.g., mitochondria, stress-fibers, and endosomes.

Here, we present a protocol to investigate the intracellular mechanical properties of isolated embryonic zebrafish cells in three-dimensional confinement with direct force measurement by an optical trap.

使用光学镊子测量禁闭中的亚细胞力学的直接力

During the development of a multicellular organism, a single fertilized cell divides and gives rise to multiple tissues with diverse functions. Tissue ...

Study of the Actin Cytoskeleton in Live Endothelial Cells Expressing GFP-Actin

The microvascular endothelium plays an important role as a selectively permeable barrier to fluids and solutes. The adhesive junctions between endothelial cells regulate permeability of the endothelium, and many studies have indicated the important contribution of the actin cytoskeleton to determining junctional integrity1-5. A cortical actin belt is thought to be important for the maintenance of stable junctions1, 2, 4, 5. In contrast, actin stress fibers are thought to generate centripetal tension within endothelial cells that weakens junctions2-5. Much of this theory has been based on studies in which endothelial cells are treated with inflammatory mediators known to increase endothelial permeability, and then fixing the cells and labeling F-actin for microscopic observation. However, these studies provide a very limited understanding of the role of the actin cytoskeleton because images of fixed cells provide only snapshots in time with no information about the dynamics of actin structures5. 
Live-cell imaging allows incorporation of the dynamic nature of the actin cytoskeleton into the studies of the mechanisms determining endothelial barrier integrity. A major advantage of this method is that the impact of various inflammatory stimuli on actin structures in endothelial cells can be assessed in the same set of living cells before and after treatment, removing potential bias that may occur when observing fixed specimens. Human umbilical vein endothelial cells (HUVEC) are transfected with a GFP-&beta;-actin plasmid and grown to confluence on glass coverslips. Time-lapse images of GFP-actin in confluent HUVEC are captured before and after the addition of inflammatory mediators that elicit time-dependent changes in endothelial barrier integrity. These studies enable visual observation of the fluid sequence of changes in the actin cytoskeleton that contribute to endothelial barrier disruption and restoration. 
Our results consistently show local, actin-rich lamellipodia formation and turnover in endothelial cells. The formation and movement of actin stress fibers can also be observed. An analysis of the frequency of formation and turnover of the local lamellipodia, before and after treatment with inflammatory stimuli can be documented by kymograph analyses. These studies provide important information on the dynamic nature of the actin cytoskeleton in endothelial cells that can used to discover previously unidentified molecular mechanisms important for the maintenance of endothelial barrier integrity.

Microscopic imaging of live endothelial cells expressing GFP-actin allows characterization of dynamic changes in cytoskeletal structures. Unlike techniques that use fixed specimens, this method provides a detailed assessment of temporal changes in the actin cytoskeleton in the same cells before, during, and after various physical, pharmacological, or inflammatory stimuli.

表达GFP -肌动蛋白的内皮细胞的肌动蛋白细胞骨架的研究

The microvascular endothelium plays an important role as a selectively permeable barrier to fluids and solutes. The adhesive junctions between endothelial ...

生物学

Fabrication and Implementation of a Reference-Free Traction Force Microscopy Platform

Quantifying cell-induced material deformation provides useful information concerning how cells sense and respond to the physical properties of their microenvironment. While many approaches exist for measuring cell-induced material strain, here we provide a methodology for monitoring strain with sub-micron resolution in a reference-free manner. Using a two-photon activated photolithographic patterning process, we demonstrate how to generate mechanically and bio-actively tunable synthetic substrates containing embedded arrays of fluorescent fiducial markers to easily measure three-dimensional (3D) material deformation profiles in response to surface tractions. Using these substrates, cell tension profiles can be mapped using a single 3D image stack of a cell of interest. Our goal with this methodology is to make traction force microscopy a more accessible and easier to implement tool for researchers studying cellular mechanotransduction processes, especially newcomers to the field.

This protocol provides instructions for implementing multiphoton lithography to fabricate three-dimensional arrays of fluorescent fiducial markers embedded in poly(ethylene glycol)-based hydrogels for use as reference-free, traction force microscopy platforms. Using these instructions, measurement of 3D material strain and calculation of cellular tractions is simplified to promote high-throughput traction force measurements.

无参考牵引力显微镜平台的制造和实施

Quantifying cell-induced material deformation provides useful information concerning how cells sense and respond to the physical properties of their ...

Traction Force Microscopy to Study B Lymphocyte Activation

Traction force microscopy (TFM) enables the measurement of forces produced by a cell on a substrate. This technique infers traction force measurements from an experimentally observed displacement field produced by a cell pulling on an elastic substrate. Here, we adapted TFM to investigate the spatial and temporal structure of the force field exerted by B cells when activated by antigen engagement of the B cell receptor. Gel rigidity, bead density, and protein functionalization must be optimized for the study of relatively small cells (~ 6 &#181;m) that interact with, and respond specifically to ligands for cell surface receptors.

Here we present a protocol used to perform traction force microscopy experiments on B cells. We describe the preparation of soft polyacrylamide gels and their functionalization, as well as data acquisition at the microscope and a summary of data analysis.

牵引力显微镜研究B淋巴细胞激活

Traction force microscopy (TFM) enables the measurement of forces produced by a cell on a substrate. This technique infers traction force measurements ...

Pattern Generation for Micropattern Traction Microscopy

Micropattern traction microscopy allows control of the shape of single cells and cell clusters. Furthermore, the ability to pattern at the micrometer length scale allows the use of these patterned contact zones for the measurement of traction forces, as each micropatterned dot allows for the formation of a single focal adhesion that then deforms the soft, underlying hydrogel. This approach has been used for a wide range of cell types, including endothelial cells, smooth muscle cells, fibroblasts, platelets, and epithelial cells. 
This review describes the evolution of techniques that allow the printing of extracellular matrix proteins onto polyacrylamide hydrogels in a regular array of dots of prespecified size and spacing. As micrometer-scale patterns are difficult to directly print onto soft substrates, patterns are first generated on rigid glass coverslips that are then used to transfer the pattern to the hydrogel during gelation. First, the original microcontact printing approach to generate arrays of small dots on the coverslip is described. A second step that removes most of the pattern to leave islands of small dots is required to control the shapes of cells and cell clusters on such arrays of patterned dots. 
Next, an evolution of this approach that allows for the generation of islands of dots using a single subtractive patterning step is described. This approach is greatly simplified for the user but has the disadvantage of a decreased lifetime for the master mold needed to make the patterns. Finally, the computational approaches that have been developed for the analysis of images of displaced dots and subsequent cell-generated traction fields are described, and updated versions of these analysis packages are provided.

We describe improvements to a standard method for measuring cellular traction forces, based on microcontact printing with a single subtractive patterning step of dot arrays of extracellular matrix proteins on soft hydrogels. This method allows for simpler and more consistent fabrication of island patterns, essential for controlling cell cluster shape.

微图案牵引显微镜的图案生成

Micropattern traction microscopy allows control of the shape of single cells and cell clusters. Furthermore, the ability to pattern at the micrometer ...

Analyses of Actin Dynamics, Clutch Coupling and Traction Force for Growth Cone Advance

To establish functional networks, neurons must migrate to their appropriate destinations and then extend axons toward their target cells. These processes depend on the advances of growth cones that located at the tips of neurites. Axonal growth cones generate driving forces by sensing their local microenvironment and modulating cytoskeletal dynamics and actin-adhesion coupling (clutch coupling). Decades of research have led to the identification of guidance molecules, their receptors, and downstream signaling cascades for regulating neuronal migration and axonal guidance; however, the molecular machineries required for generating forces to drive growth cone advance and navigation are just beginning to be elucidated. At the leading edge of neuronal growth cones, actin filaments undergo retrograde flow, which is powered by actin polymerization and actomyosin contraction. A clutch coupling between F-actin retrograde flow and adhesive substrate generates traction forces for growth cone advance. The present study describes a detailed protocol for monitoring F-actin retrograde flow by single speckle imaging. Importantly, when combined with an F-actin marker Lifeact, this technique can quantify 1) the F-actin polymerization rate and 2) the clutch coupling efficiency between F-actin retrograde flow and the adhesive substrate. Both are critical variables for generating forces for growth cone advance and navigation. In addition, the present study describes a detailed protocol of traction force microscopy, which can quantify 3) traction force generated by growth cones. Thus, by coupling the analyses of&#160;single speckle imaging and traction force microscopy, investigators can monitor the molecular mechanics underlying growth cone advance and navigation.

To advance, growth cones must exert traction forces against the external environment. The generation of traction forces is dependent on actin dynamics and clutch coupling. The present study describes methods for analyzing actin dynamics, clutch coupling and traction forces for growth cone advance.

肌动蛋白动力学、离合器耦合和牵引力分析，促进生长锥体前进

To establish functional networks, neurons must migrate to their appropriate destinations and then extend axons toward their target cells. These processes ...