Kwinter David M, Silverman Michael A
Department of Biological Sciences, Simon Fraser University, Canada.
J Vis Exp. 2009 May 29(27):1144. doi: 10.3791/1144.
Observing and characterizing dynamic cellular processes can yield important information about cellular activity that cannot be gained from static images. Vital fluorescent probes, particularly green fluorescent protein (GFP) have revolutionized cell biology stemming from the ability to label specific intracellular compartments and cellular structures. For example, the live imaging of GFP (and its spectral variants) chimeras have allowed for a dynamic analysis of the cytoskeleton, organelle transport, and membrane dynamics in a multitude of organisms and cell types [1-3]. Although live imaging has become prevalent, this approach still poses many technical challenges, particularly in primary cultured neurons. One challenge is the expression of GFP-tagged proteins in post-mitotic neurons; the other is the ability to capture fluorescent images while minimizing phototoxicity, photobleaching, and maintaining general cell health. Here we provide a protocol that describes a lipid-based transfection method that yields a relatively low transfection rate (~0.5%), however is ideal for the imaging of fully polarized neurons. A low transfection rate is essential so that single axons and dendrites can be characterized as to their orientation to the cell body to confirm directionality of transport, i.e., anterograde v. retrograde. Our approach to imaging GFP expressing neurons relies on a standard wide-field fluorescent microscope outfitted with a CCD camera, image capture software, and a heated imaging chamber. We have imaged a wide variety of organelles or structures, for example, dense-core vesicles, mitochondria, growth cones, and actin without any special optics or excitation requirements other than a fluorescent light source. Additionally, spectrally-distinct, fluorescently labeled proteins, e.g., GFP and dsRed-tagged proteins, can be visualized near simultaneously to characterize co-transport or other coordinated cellular events. The imaging approach described here is flexible for a variety of imaging applications and can be adopted by a laboratory for relatively little cost provided a microscope is available.
观察和表征动态细胞过程可以产生有关细胞活动的重要信息,而这些信息无法从静态图像中获得。重要的荧光探针,特别是绿色荧光蛋白(GFP),因其能够标记特定的细胞内区室和细胞结构,给细胞生物学带来了革命性变化。例如,GFP(及其光谱变体)嵌合体的实时成像使得对多种生物体和细胞类型中的细胞骨架、细胞器运输和膜动力学进行动态分析成为可能[1-3]。尽管实时成像已变得普遍,但这种方法仍然带来许多技术挑战,尤其是在原代培养的神经元中。一个挑战是有丝分裂后神经元中GFP标记蛋白的表达;另一个挑战是在将光毒性、光漂白降至最低并维持细胞整体健康的同时捕获荧光图像的能力。在这里,我们提供了一种方案,描述了一种基于脂质的转染方法,该方法产生的转染率相对较低(约0.5%),但对于完全极化神经元的成像来说是理想的。低转染率至关重要,这样单个轴突和树突就可以根据它们相对于细胞体的方向来表征,以确认运输的方向性,即顺行与逆行。我们对表达GFP的神经元进行成像的方法依赖于配备了电荷耦合器件(CCD)相机、图像采集软件和加热成像室的标准宽视野荧光显微镜。我们已经对多种细胞器或结构进行了成像,例如致密核心囊泡、线粒体、生长锥和肌动蛋白,除了荧光光源外,无需任何特殊光学器件或激发要求。此外,光谱不同的荧光标记蛋白,例如GFP和dsRed标记蛋白,可以近乎同时可视化,以表征共运输或其他协调的细胞事件。这里描述的成像方法对于各种成像应用具有灵活性,并且如果有显微镜可用,实验室以相对较低的成本就可以采用。