检测和DNA损伤分析小鼠骨骼肌<em>原位</em>使用TUNEL法
Summary
This video describes dissection, tissue processing, sectioning, and fluorescence-based TUNEL labeling of mouse skeletal muscle. It also describes a method for semi-automated analysis of TUNEL labeling.
Abstract
Terminal deoxynucleotidyl transferase (TdT) deoxyuridine triphosphate (dUTP) nick end labeling (TUNEL) is the method of using the TdT enzyme to covalently attach a tagged form of dUTP to 3’ ends of double- and single-stranded DNA breaks in cells. It is a reliable and useful method to detect DNA damage and cell death in situ. This video describes dissection, tissue processing, sectioning, and fluorescence-based TUNEL labeling of mouse skeletal muscle. It also describes a method of semi-automated TUNEL signal quantitation. Inherent normal tissue features and tissue processing conditions affect the ability of the TdT enzyme to efficiently label DNA. Tissue processing may also add undesirable autofluorescence that will interfere with TUNEL signal detection. Therefore, it is important to empirically determine tissue processing and TUNEL labeling methods that will yield the optimal signal-to-noise ratio for subsequent quantitation. The fluorescence-based assay described here provides a way to exclude autofluorescent signal by digital channel subtraction. The TUNEL assay, used with appropriate tissue processing techniques and controls, is a relatively fast, reproducible, quantitative method for detecting apoptosis in tissue. It can be used to confirm DNA damage and apoptosis as pathological mechanisms, to identify affected cell types, and to assess the efficacy of therapeutic treatments in vivo.
Introduction
双和单链DNA断裂12,23末端脱氧核苷酸转移酶（TDT）缺口末端标记（TUNEL）是利用末端转移酶酶连接的dUTP 3的进程的结束。 TUNEL法检测细胞凋亡和DNA损伤的由Gavrieli 等人 1,12,24首次报道在20年前。它已经被评估，并在不同的组织筹备7,23,27,40优化。 TUNEL法已被用于研究局部缺血诱导的细胞死亡的神经元6,14,29和心肌43,44的，兴奋毒性神经元细胞死亡30,31，并作为在关节炎治疗39的生物标记物。它也被用作在各种人类癌症2,3,15,32,37,38,42的预后因子和肿瘤细胞标记物。
DNA损伤和细胞死亡检测的替代方法存在，但他们有技术挑战和警告。 Southern印迹可用于quantifýDNA损伤在整个组织裂解7,9-11，但这种方法不提供蜂窝级别分辨率和难以量化。彗星试验是需要从细胞中提取4,20,28,36保存细胞核的替代的基于细胞的方法。虽然彗星试验工作良好对培养分离的细胞，它是更难以从骨骼肌组织8,21准备完整的细胞核。如同Southern印迹，彗星试验不提供从全肌肉组织匀浆细胞类型特定的信息。另一个替代TUNEL法是使用抗单链DNA 25,33,41或针对参与DNA损伤应答和细胞死亡途径（ 如 p53基因，H2AX，和半胱氨酸蛋白酶）13,17,22,40蛋白免疫组织化学。这样的基于抗体的方法需要的抗体的透彻表征和优异的抗体特异性，以产生一个高的信号 – 背景比。即使在规格IFIC抗体存在，它们可能需要通过抗原修复程序34,35变性靶蛋白。正如我们在这里讨论，抗原修复肌肉组织会导致不可接受的高自发荧光。不像其他方法，TUNEL实现DNA损伤检测具有高信号和低背景，特异性好，可以用简单的阳性和阴性对照，良好的组织穿透，不需要抗原修复和细胞级的分辨率进行测试。此外，TUNEL法需要大约4小时，以完成的，而另一种方法通常需要过夜孵育。
我们研究骨骼肌细胞死亡的脊髓性肌萎缩症（SMA）10是由谢，李和他的同事16产生的小鼠模型。为了量化凋亡细胞中的肌，我们开发了组织制备，染色和定量的方法，其工作原理鲁棒跨不同skeleTAL肌肉群在小鼠不同发育时间点。我们用市售的TUNEL标记试剂盒和市售的图像分析软件。我们也成功地使用了TUNEL测定结合免疫荧光染色在脊髓10。
此处所描述的方法是谁想要以评估骨骼肌组织病理学，疾病的机制，老化机制，和发育（前和产后）细胞死亡的调查是有用的。的TUNEL技术是DNA损伤和修复和细胞死亡在模型系统中，其中的细胞的一个子集是受影响和细胞水平分辨率是必要的研究特别有用。
这部影片描述了解剖，组织处理，切片，与小鼠骨骼肌基于荧光的TUNEL标记。它还描述了半自动化的TUNEL信号定量的方法。
Protocol
Representative Results
Discussion
的方法来检测和描述定量分析DNA损伤相关的细胞凋亡的小鼠骨骼肌。该过程包括组织收获，TUNEL染色，数字图像采集和图像分析。需要常见的组织学用品，工具，以及一个特殊的商业的TUNEL试剂盒是必要的。所需的基本的大设备项目是一个低温恒温器，落射荧光显微镜用数字图像的能力，以及用于图像分析的计算机系统。
实验者应该意识到潜在的陷阱。组织自发荧光的荧光成?…
Disclosures
The authors have nothing to disclose.
Acknowledgements
This work was supported by NIH-NINDS grant RO1-NS065895 and NIH-NINDS grant 5-F31-NS076250-02.
We thank JHU SOM Microscope Facility for the use of the cryostat.
Materials
| Name of Reagent/ Equipment | Company | Catalog Number | Comments/Description |
| 4% Paraformaldehyde in phosphate buffered saline | Electron Microscopy Sciences | 19202 | For procedures described here, 4% solution was prepared fresh from powder. Paraformaldehyde from any supplier may be used. Prepared formaldehyde solution should be stored at 4 °C and should not be used after its expiration date (up to several months). Paraformaldehyde is a carcinogen and a toxin by inhalation and skin contact. Please follow precautions specified in the MSDS when handling paraformaldehyde. |
| Sucrose | Sigma | S0389 | Used for cryoprotecting tissue before freezing. Sucrose from any supplier may be used. |
| O.C.T. compound | Tissue-Tek | 4583 | Embedding medium for cryosectioning. |
| Cryostat | Leica | CM 3050S | A Leica CM3050S cryostat was used for the preparations described here. Any cryostat capable of cutting 10 μm sections may be used. |
| Glass slides, 25 x 75 x 1 mm | Fisher | 12-552-3 | Slides from any supplier may be used. |
| Gelatin | Sigma | G-9391 | Gelatin is used to promote tissue section adhesion to glass slides. To coat glass slides with gelatin, dissolve 2.75 g gelatin and 0.275 g chrome alum in 500 mL distilled water, warm to 60 °C, dip slides for several seconds, and let dry. Gelatin from any supplier may be used. Alternatively, gelatin-precoated slides may be purchased. |
| Chromium(III) potassium sulfate dodecahydrate (chrome alum) | Sigma | 243361 | Chrome alum is added to gelatin solution to promote tissue adhesion on glass slides. It is a possible carcinogen and a toxin by inhalation and skin contact. Please follow precautions specified in the MSDS when handling chrome alum. |
| Vectabond tissue adhesion reagent | Vector Labs | SP-1800 | Optional substrate for better tissue adhesion to glass slides; gellatin-coated slides may be used instead. |
| Tween20 | Sigma | P9416 | A detergent used to permeabilize tissue. Tween20 from any supplier may be used. |
| Triton X100 | Sigma | T8787 | A detergent used to permeabilize tissue. Triton X100 from any supplier may be used. |
| TACS 2 TdT fluorescein in situ apoptosis detection kit | Trevigen | 4812-30-K | Commercial kit for fluorescence-based TUNEL labeling. |
| DNase/nuclease | Trevigen | 4812-30-K | (included with kit) |
| DNase/nuclease buffer | Trevigen | 4812-30-K | (included with kit) |
| 10x phosphate buffered saline (PBS), pH 7.4 | Amresco | 780 | Make 1x PBS for washes and dilutions. PBS from any supplier may be used. |
| DNase-free water | Quality Biologicals | 351-029-131 | Water from any supplier may be used. |
| Hoechst 33258 | Sigma | 94403 | Nuclear dye. Any blue fluorescent nuclear dye may be used. As a DNA-binding dye, Hoechst is a suspected carcinogen and should be handled with protective equipment to minimize skin contact. |
| Parafilm M | multiple | 807 | Any other hydrophobic film or cover slip may be used. Available from multiple suppliers. |
| Fluorescent microscope with digital camera | – | – | Any fluorescent microscope capable of digitally capturing red, green, and blue fluorescence in separate channels may be used. |
| Vectashield antifade media | Vector Labs | H-1000 | Antifade media from any supplier may be used. |
| glass coverslips, No.1 thickness | Brain Research Labs | 2222-1 | Cover slips from any supplier may be used. The smallest size of 22×22 mm is sufficient for neonatal mouse leg sections. |
| Nail polish | Ted Pella | 114-8 | Used to seal coverslips. Nail polish from any supplier (including regular retailers) may be used. Avoid using nail polish with color or additives that may reflect light during fluorescent imaging. |
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