Summary

المقاصة البصري للنظام العصبي المركزي الماوس عن طريق وضوح السلبي

Published: June 30, 2016
doi:

Summary

Optical clearing techniques are revolutionizing the way tissues are visualized. In this report we describe modifications of the original Clear Lipid-exchanged Acrylamide-hybridized Rigid Imaging-compatible Tissue-hYdrogel (CLARITY) protocol that yields more consistent and less expensive results.

Abstract

Traditionally, tissue visualization has required that the tissue of interest be serially sectioned and imaged, subjecting each tissue section to unique non-linear deformations, dramatically hampering one’s ability to evaluate cellular morphology, distribution and connectivity in the central nervous system (CNS). However, optical clearing techniques are changing the way tissues are visualized. These approaches permit one to probe deeply into intact organ preparations, providing tremendous insight into the structural organization of tissues in health and disease. Techniques such as Clear Lipid-exchanged Acrylamide-hybridized Rigid Imaging-compatible Tissue-hYdrogel (CLARITY) achieve this goal by providing a matrix that binds important biomolecules while permitting light-scattering lipids to freely diffuse out. Lipid removal, followed by refractive index matching, renders the tissue transparent and readily imaged in 3 dimensions (3D). Nevertheless, the electrophoretic tissue clearing (ETC) used in the original CLARITY protocol can be challenging to implement successfully and the use of a proprietary refraction index matching solution makes it expensive to use the technique routinely. This report demonstrates the implementation of a simple and inexpensive optical clearing protocol that combines passive CLARITY for improved tissue integrity and 2,2′-thiodiethanol (TDE), a previously described refractive index matching solution.

Introduction

The ability to image complete neuroanatomical structures is immensely valuable for understanding the brain in health and disease. Traditionally, 3D imaging has required tissue sectioning to provide the axial resolution and to visualize deep anatomical structures. This approach can produce high-resolution data sets, but requires sophisticated image reconstruction techniques and is very labor intensive. As a result, it has been limited to the imaging of small volumes of tissue1-3. Optical sectioning, on the other hand, is well suited for the creation of high-resolution 3D images of fluorescently labeled tissues. Since optical sectioning is inherently three dimensional, it does not require extensive computation to produce a 3D image volume. However, light scattering and tissue opacity limit the depth at which tissues can be optically sectioned. The depth of imaging is limited to about 150 µm in laser scanning confocal microscopy and to less than 800 µm using two-photon excitation microscopy4-8.

In order to overcome these limitations, several optical clearing techniques have been recently developed and then further refined to permit the deep microscopic imaging of intact tissues. The use of benzyl alcohol and benzyl benzoate (BABB) to render fixed tissues transparent was among one of the earliest approaches9. However, this approach was limited by the quenching of fluorescence in the samples and incomplete clearing of highly myelinated structures10. Refinements of this technique, such as 3D Imaging of Solvent Cleared Organs (3DISCO), have led to very rapid and complete tissue clearing, but still suffer from rapid loss of fluorescent signals, especially yellow fluorescent protein (YFP)10. Water-based clearing solutions, such as Sca/e11 and SeeDB12, preserve fluorescent signals, but do not completely clear highly myelinated tissues. Clear, Unobstructed Brain Imaging Cocktails and Computational analysis (CUBIC) is a promising new optical clearing technology that appears to overcome the limitations of previously developed water-based clearing solutions13. In contrast with other optical clearing techniques, Clear Lipid-exchanged Acrylamide-hybridized Rigid Imaging-compatible Tissue-hYdrogel (CLARITY)14 embeds the brain in a porous matrix that provides structural integrity to proteins, nucleic acids and small molecules, while leaving lipids unbound. The lipids are then removed electrophoretically, culminating in an optically cleared brain that can be easily visualized and equally easily probed using commonly available techniques.

Electrophoretic tissue clearing (ETC) is used to remove lipids from hydrogel embedded tissues in CLARITY, however, ETC can be difficult to implement consistently and tissues subject to electrophoresis can exhibit tissue distortion, browning, loss of fluorescence and antibody reactivity. Passive lipid clearing avoids these limitations, but requires increased clearing times15-17. Passive clearing also permits the clearing of large numbers of samples in parallel, since it is not limited by the number of ETC apparatuses available. Decreasing the concentration of paraformaldehyde and excluding bis-acrylamide from the hydrogel have led to great increases in the speed of clearing at the expense of greater tissue expansion16. Less expensive alternatives to the refractive index matching solution used in the original CLARITY technique have been developed17-19. 2,2′-thiodiethanol (TDE) is an inexpensive and rapid brain clearing agent that reverses some of the tissue expansion that occurs during lipid removal18. This report incorporates passive clearing of hydrogel embedded tissue and the use of TDE as a refractive index matching solution to the original CLARITY technique to produce a highly reproducible and inexpensive protocol for the optical clearing of the mouse central nervous system.

Protocol

أجريت جميع التجارب وفقا للرعاية الحيوان المؤسسية والمبادئ التوجيهية للجنة الاستخدام (IACUC). استخدمت THY1-YFP، حزب العمال التقدمي-EGFP وPV-TdTomato الفئران لهذه التجارب، ولكن أي الفئران معربا عن البروتينات الفلورية يمكن مسح بنجاح وتصويرها. 1. …

Representative Results

تصور التنظيم الهيكلي للدماغ أمر بالغ الأهمية لفهم كيفية التشكل والاتصال تؤثر على وظيفة الدماغ في الصحة والمرض. تقنيات المقاصة البصرية تجعل من الممكن لسكان الخلية الصورة في 3D في الأنسجة سليمة، مما يسمح لنا لدراسة مورفولوجية والربط متماسك. <p class="jov…

Discussion

المقاصة سلبية من هيدروجيل جزءا لا يتجزأ من الأنسجة (وضوح السلبي) هي طريقة بسيطة وغير مكلفة لإزالة أجزاء كبيرة من الأنسجة. لا يتطلب هذا النهج معدات مخصصة، ويمكن بسهولة أن يؤديها في شاكر التحكم في درجة حرارته. على مدى غضون بضعة أسابيع، حتى الكبيرة، والأنسجة العصبي للغا?…

Divulgations

The authors have nothing to disclose.

Acknowledgements

وأيد هذا العمل بسخاء من قبل المعاهد الوطنية لل/ معهد الصحة الوطني للاضطرابات العصبية والسكتة الدماغية (NIH / NINDS) منحة 1R01NS086981 ومؤسسة كونراد هيلتون. نشكر الدكتور لوران Bentolila والدكتور ماثيو Schibler للمساعدة لا تقدر بثمن مع المجهر متحد البؤر. نشكر تلك التي ساهمت في المنتدى ضوح (http://forum.claritytechniques.org). نخص بالشكر الدكتور كارل Deisseroth لفتح مختبره لتعليم هذه التقنية الرائعة. الكتاب ممتنون للدعم السخي من منظمة الدماغ رسم الخرائط الأبحاث الطبية، ومؤسسة الدماغ رسم الخرائط دعم، بيرسون-افليس مؤسسة، مؤسسة Ahmanson، مجموعة شركات رأس المال للأعمال الخيرية، ويليام م وليندا صندوق الخيرية Dietel R.، وصندوق نورث ستار . تم البحث عنها في هذا المنشور أيضا بدعم جزئي من قبل المركز الوطني للبحوث الموارد ومكتب المدير الأمةآل معاهد الصحة تحت أرقام جائزة C06RR012169، C06RR015431، وS10OD011939. المحتوى هو فقط من مسؤولية الكتاب ولا تمثل بالضرورة وجهة النظر الرسمية للمعاهد الوطنية للصحة.

Materials

10X phosphate buffered saline (PBS) Fisher BP399-1 buffers
32% paraformaldehyde (PFA) Electron Microscopy Sciences 15714-5 perfusion and hydrogel
2,2'-thiodiethanol (TDE) Sigma-Aldrich 166782-500G refractive index matching solution
40% acrylamide Bio-Rad 161-0140 hydrogel
2% bis-acrylamide Bio-Rad 161-0142 hydrogel
VA-044 initiator Wako Pure Chemical Industries, Ltd. VA044 hydrogel
boric acid Sigma-Aldrich B7901 clearing buffer
sodium dodecyl sulfate (SDS) Fisher BP166-5 clearing buffer
sodium hydroxide Fisher 55255-1 buffers
sodium azide Sigma-Aldrich 52002-100G preservative
triton x-100 Sigma-Aldrich X100-500G buffers
heparin Sigma-Aldrich H3393-50KU perfusion
sodium nitrate Fisher BP360-500 perfusion
DAPI Molecular Probes D1306 nuclear stain
99.9% isoflurane Phoenix 57319-559-06 anesthetic
hydrocholoric acid Fisher A1445-500 buffers
glass bottom dish Willco HBSB-5040 Willco dishes
reusable adhesive Bostick 371351 Blu-Tack
silicon elastomer World Precision Instruments KWIK-CAST Kwik-Cast
lint-free wipe Kimberly-Clark 34120 KimWipe
mouse brain matrix Roboz SA-2175 sectioning tissue
matrix blades Roboz RS-9887 sectioning tissue
peristaltic pump Cole-Parmer 77122-24 pefusion
laser scanning confocal microscope Leica SP5 microscopy
imaging software Leica LAS AF microscopy

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Roberts, D. G., Johnsonbaugh, H. B., Spence, R. D., MacKenzie-Graham, A. Optical Clearing of the Mouse Central Nervous System Using Passive CLARITY. J. Vis. Exp. (112), e54025, doi:10.3791/54025 (2016).

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