Name: adipo-clear: a tissue clearing method for three-dimensional imaging of adipose tissue
Uploaded: 2018-07-28T15:00:00
Description: Watch this Scientific Journal Video about Adipo-Clear: A Tissue Clearing Method for Three-Dimensional Imaging of Adipose Tissue at JoVE.com

We thank Christina Pyrgaki, Tao Tong, and Alison North from the Bioimaging Resource Center at the Rockefeller University for assistance and support. We also thank Xiphias Ge Zhu for movie editing. This work was supported by the Human Frontier Science Program Organization (PC).

Animal care and experimentation were performed according to procedures approved by the Institutional Animal Care and Use Committee at the Rockefeller University.
1. Tissue Preparation
<ol>
	<li>Perform standard intracardiac perfusion with ~20 mL of 1x phosphate buffered saline (PBS) at 4 &#176;C until the blood is completely removed from the tissue.</li>
	<li>Switch the perfusate to ~20 mL of fixative solution (4% paraformaldehyde (PFA) in 1x PBS) at 4 &#176;C until the neck and tail have si...

<ol>
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J., Tupone, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Central+Neural+Regulation+of+Brown+Adipose+Tissue+Thermogenesis+and+Energy+Expenditure.">Central Neural Regulation of Brown Adipose Tissue Thermogenesis and Energy Expenditure.</a> Cell Metabolism. 19 (5), 741-756 (2014).</li><li>Xue, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hypoxia-Independent+Angiogenesis+in+Adipose+Tissues+during+Cold+Acclimation.">Hypoxia-Independent Angiogenesis in Adipose Tissues during Cold Acclimation.</a> Cell Metabolism. 9 (1), 99-109 (2009).</li><li>Shimizu, I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vascular+rarefaction+mediates+whitening+of+brown+fat+in+obesity.">Vascular rarefaction mediates whitening of brown fat in obesity.</a> The Journal of Clinical Investigation. 124 (5), 2099-2112 (2014).</li><li>Abe, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=3D+reconstruction+of+brain+section+images+for+creating+axonal+projection+maps+in+marmosets.">3D reconstruction of brain section images for creating axonal projection maps in marmosets.</a> Journal of Neuroscience Methods. 286, 102-113 (2017).</li><li>Richardson, D. S., Lichtman, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Clarifying+Tissue+Clearing.">Clarifying Tissue Clearing.</a> Cell. 162 (2), 246-257 (2015).</li><li>Renier, N., Wu, Z., Simon, D. J., Yang, J., Ariel, P., Tessier-Lavigne, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=iDISCO:+A+Simple,+Rapid+Method+to+Immunolabel+Large+Tissue+Samples+for+Volume+Imaging.">iDISCO: A Simple, Rapid Method to Immunolabel Large Tissue Samples for Volume Imaging.</a> Cell. 159 (4), 896-910 (2014).</li><li>Renier, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mapping+of+Brain+Activity+by+Automated+Volume+Analysis+of+Immediate+Early+Genes.">Mapping of Brain Activity by Automated Volume Analysis of Immediate Early Genes.</a> Cell. 165 (7), 1789-1802 (2016).</li><li>Chi, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-Dimensional+Adipose+Tissue+Imaging+Reveals+Regional+Variation+in+Beige+Fat+Biogenesis+and+PRDM16-Dependent+Sympathetic+Neurite+Density.">Three-Dimensional Adipose Tissue Imaging Reveals Regional Variation in Beige Fat Biogenesis and PRDM16-Dependent Sympathetic Neurite Density.</a> Cell Metabolism. 27 (1), 226-236 (2018).</li><li>Khan, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metabolic+Dysregulation+and+Adipose+Tissue+Fibrosis:+Role+of+Collagen+VI.">Metabolic Dysregulation and Adipose Tissue Fibrosis: Role of Collagen VI.</a> Molecular and Cellular Biology. 29 (6), 1575-1591 (2009).</li><li>Croce, A. C., Bottiroli, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Autofluorescence+Spectroscopy+and+Imaging:+A+Tool+for+Biomedical+Research+and+Diagnosis.">Autofluorescence Spectroscopy and Imaging: A Tool for Biomedical Research and Diagnosis.</a> European Journal of Histochemistry EJH. 58 (4), (2014).</li><li>Oh, D. Y., Morinaga, H., Talukdar, S., Bae, E. J., Olefsky, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Increased+Macrophage+Migration+Into+Adipose+Tissue+in+Obese+Mice.">Increased Macrophage Migration Into Adipose Tissue in Obese Mice.</a> Diabetes. 61 (2), 346-354 (2012).</li><li>Cinti, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adipocyte+death+defines+macrophage+localization+and+function+in+adipose+tissue+of+obese+mice+and+humans.">Adipocyte death defines macrophage localization and function in adipose tissue of obese mice and humans.</a> Journal of Lipid Research. 46 (11), 2347-2355 (2005).</li><li>Wang, W., Seale, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Control+of+brown+and+beige+fat+development.">Control of brown and beige fat development.</a> Nature Reviews Molecular Cell Biology. 17 (11), 691-702 (2016).</li></ol>

Adipo-Clear is a straightforward and robust method for clearing adipose tissue, which can be easily performed in a regular lab setup. In comparison to other solvent-based clearing methods such as iDISCO/iDISCO+10,11,12, Adipo-Clear is particularly optimized for clearing adipose tissue and other tissue with high fat content. The delipidation step completely removes lipids from adipose, and therefore facilitates immunolabeling thr...

Until recently, adipose tissue was conceived of as an amorphous collection of fat cells. Over the past few decades, our understanding has grown more sophisticated, with fat now recognized to be a complex organ containing different types of adipocytes, as well as adipocyte precursors, immune cells, fibroblasts, the vasculature, and nerve projections. Interactions among these adipose-resident cells have pronounced effects on adipose tissue and organismal physiology and pathophysiology1. Although emerging studies have unraveled important molecular mechanisms underlying certain interactions, a more comprehensive understanding requires reliable structural profiling of the entire tissue in three dimensions (3D).
Our current knowledge of adipose tissue morphology is largely based on histological analysis of thin sections (5 &#956;m) with relatively high-magnification imaging (more than 10X)2,3. However, this approach has several significant limitations. First, intricate filamentous structures such as sympathetic nerves and the vasculature, which are known to play important roles in adipose function4,5,6,7, are difficult to evaluate through thin sections. Second, due to its seemingly amorphous shape and the lack of representative structural units to focus on, it is difficult to appreciate adipose tissue structures based only on section staining. Third, adipose tissue has a very high lipid content, creating challenges in obtaining consistent serial sections that are suitable for 3D anatomical reconstruction, a conventional method used to study whole brain morphology8. Given these factors, there is a great need for a whole-mount approach that can provide 3D visualization of an entire adipose depot while still achieving cellular resolution.
3D volumetric imaging of an entire organ is challenging due to the obscuring effects of light scatter. A major source of light scatter in biological tissues comes from lipid-aqueous interfaces. Although the efforts to eliminate scatter by removing lipids have been ongoing for over a century, there have been a large number of recent innovations9. One such newly developed tissue-clearing method is immunolabeling-enabled 3D imaging of solvent-cleared organs (iDISCO/iDISCO+)10,11. However, adipose tissue presents a particular challenge given its high level of lipids, and therefore, additional modifications to the iDISCO/iDISCO+ protocol are required to fully extract the lipids while protecting the tissue from collapsing. The modified protocol we have developed, now called Adipo-Clear, employs methanol/dichloromethane-based delipidation of adipose tissue to achieve optimal transparency suitable for high-resolution volumetric imaging12. Because the delipidation step largely quenches endogenously expressed fluorescent proteins such as GFP and RFP, visualization of such proteins must be achieved by immunolabeling. Overall, this simple and robust protocol can be applied to study tissue-level organization of adipose-resident cells, lineage tracing of adipocyte progenitor cells, and adipose morphogenesis during development.

<table>
	<tbody>
		<tr>
			<td>1x phosphate buffered saline</td>
			<td>Corning</td>
			<td>21-040-CV</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>Sigma Aldrich</td>
			<td>P6148-1KG</td>
			<td></td>
		</tr>
		<tr>
			<td>Methanol</td>
			<td>Fisher Scientific</td>
			<td>A412SK-4</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Sigma Aldrich</td>
			<td>X100-500ML</td>
			<td></td>
		</tr>
		<tr>
			<td>Tween 20</td>
			<td>Sigma Aldrich</td>
			<td>P2287-500ML</td>
			<td></td>
		</tr>
		<tr>
			<td>Heparin</td>
			<td>Sigma Aldrich</td>
			<td>H3393-100KU</td>
			<td></td>
		</tr>
		<tr>
			<td>Dichloromethane</td>
			<td>Sigma Aldrich</td>
			<td>270991</td>
			<td></td>
		</tr>
		<tr>
			<td>Hydrogen peroxide 30%</td>
			<td>Fisher Scientific</td>
			<td>325-100</td>
			<td></td>
		</tr>
		<tr>
			<td>Benzyl ether</td>
			<td>Sigma Aldrich</td>
			<td>108014</td>
			<td></td>
		</tr>
		<tr>
			<td>Agarose</td>
			<td>Invitrogen</td>
			<td>16500500</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium azide</td>
			<td>Sigma Aldrich</td>
			<td>71289-5G</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycine</td>
			<td>Fisher Scientific</td>
			<td>BP381-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Rabbit polyclonal anti-Tyrosine Hydroxylase</td>
			<td>Millipore</td>
			<td>AB152</td>
			<td>1:200 dilution</td>
		</tr>
		<tr>
			<td>Goat polyclonal anti-CD31/PECAM-1</td>
			<td>R&#38;D Systems</td>
			<td>AF3628</td>
			<td>Final concentration of 2 &#181;g/mL</td>
		</tr>
		<tr>
			<td>Rat monoclonal anti-CD68, Clone FA-11</td>
			<td>Bio-Rad</td>
			<td>MCA1957</td>
			<td>Final concentration of 2 &#181;g/mL</td>
		</tr>
		<tr>
			<td>Donkey anti-rabbit IgG (H+L) Alexa Fluor 647</td>
			<td>Jackson ImmunoResearch</td>
			<td>711-605-152</td>
			<td>Final concentration of 5-10 &#181;g/mL</td>
		</tr>
		<tr>
			<td>Donkey anti-goat IgG (H+L) Alexa Fluor 568</td>
			<td>Invitrogen</td>
			<td>A11077</td>
			<td>Final concentration of 5-10 &#181;g/mL</td>
		</tr>
		<tr>
			<td>Donkey anti-rat IgG (H+L) Alexa Fluor 647</td>
			<td>Jackson ImmunoResearch</td>
			<td>712-605-153</td>
			<td>Final concentration of 5-10 &#181;g/mL</td>
		</tr>
		<tr>
			<td>Imaging chamber</td>
			<td>ibidi</td>
			<td>80287</td>
			<td></td>
		</tr>
		<tr>
			<td>Light sheet microscope</td>
			<td>LaVision BioTec</td>
			<td>Ultramicroscope II</td>
			<td></td>
		</tr>
		<tr>
			<td>Imaging software</td>
			<td>LaVision BioTec</td>
			<td>Imspector software</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscopy visualization software</td>
			<td>Bitplane</td>
			<td>Imaris</td>
			<td></td>
		</tr>
	</tbody>
</table>

adipo-clear: a tissue clearing method for three-dimensional imaging of adipose tissue

Adipose tissue plays a central role in energy homeostasis and thermoregulation. It is composed of different types of adipocytes, as well as adipocyte precursors, immune cells, fibroblasts, blood vessels, and nerve projections. Although the molecular control of cell type specification and how these cells interact have been increasingly delineated, a more comprehensive understanding of these adipose-resident cells can be achieved by visualizing their distribution and architecture throughout the whole tissue. Existing immunohistochemistry and immunofluorescence approaches to analyze adipose histology rely on thin paraffin-embedded sections. However, thin sections capture only a small portion of tissue; as a result, the conclusions can be biased by what portion of tissue is analyzed. We have therefore developed an adipose tissue clearing technique, Adipo-Clear, to permit comprehensive three-dimensional visualization of molecular and cellular patterns in whole adipose tissues. Adipo-Clear was adapted from iDISCO/iDISCO+, with specific modifications made to completely remove the lipid stored in the tissue while preserving native tissue morphology. In combination with light-sheet fluorescence microscopy, we demonstrate here the use of the Adipo-Clear method to obtain high-resolution volumetric images&#160;of an entire adipose tissue.

Adipo-Clear prepared whole fat pads can be imaged in 3D to analyze how tissue morphology and cellular interactions are affected in the lean and obese states. This method can be easily applied to analyze general adipose structure by collecting the tissue autofluorescence signal in the green channel. We have previously shown that the autofluorescence signal in adipose overlays favorably with perilipin staining, a commonly used marker to outline mature adipocytes12. F...

Watch this Scientific Journal Video about Adipo-Clear: A Tissue Clearing Method for Three-Dimensional Imaging of Adipose Tissue at JoVE.com

Adipo-Clear: A Tissue Clearing Method for Three-Dimensional Imaging of Adipose Tissue

Due to the high lipid content, adipose tissue has been challenging to visualize using traditional histological methods. Adipo-Clear is a tissue clearing technique that allows robust labeling and high-resolution volumetric fluorescent imaging of adipose tissue. Here, we describe the methods for sample preparation, pretreatment, staining, clearing, and mounting for imaging.

Adipose tissue plays a central role in energy homeostasis and thermoregulation. It is composed of different types of adipocytes, as well as adipocyte ...

This method can help answer key questions in the field of Adipose Tissue Biology, such as how different components of Adipose Tissue interact in an entire tissue. The main advantage of this technique is that it fully removes the excess lipids stored in Adipose Tissue while maintaining it's three-dimensional architecture. While this method can provide insight into those three-dimensional organization of Adipose Tissue it can also be generally applied to other tissues with high lipid content such as memory gland and lymph node.Visual demonstration of this method is critical as the delipidation and the clearing steps require sufficient incubation times, which can be difficult to determine. Begin by using blunt ended forceps to dissect the fat pad of interest from a freshly perfused animal model. Carefully remove the entire fad pad without pinching or squeezing the tissue or contamination the dissected tissue with fur.Place the fat pad in approximately 10 milliliters of fixation solution in a 15 milliliter conical tube and post fix at four degrees celsius overnight. The next day after washing the sample with PBS, gently remove any debris from the sample under a dissection microscope. Hair, lint, or other debris attached to the sample will cause shadows during imaging.Transfer the clean sample to a polypropylene tube containing ice cold, 20 percent methanol B1N buffer. Place the tube containing the sample horizontally on an orbital shaker, set it 100 RPM, and shake for 30 minutes to 1 hour depending on the size of the sample. Ensure the samples can move freely inside the tube.Continue dehydrating the samples through a graded series of 40 percent, 60 percent, and 80 percent methanol in B1N buffer followed by 100 percent methanol. Minimize the carryover solution. Following dehydration, replace the 100 percent methanol solution with 100 percent dichloromethane or DCM to delipidate the sample.Repeat the wash twice following the incubation times listed in table 2. The sample should sink to the bottom of the tube at the end of the second and third DCM washes. If not, extend the incubation time to ensure full delipidation.After delipidation, wash twice with 100 percent methanol for the time indicated in table 2. Rehydrate the sample in a reversed methanol B1N buffer series for the times indicated in table 2. After rehydration, wash the sample with PTXWH buffer for 2 hours at room temperature.The sample is now ready for immunostaining or could be stored in PTXWH buffer at 4 degrees celsius for up to 1 year. First, dilute the primary antibody in PTXWH buffer to the recommended concentration. Then, centrifuge the diluted antibody solution at 20 thousand G for 10 minutes to prevent introducing antibody precipitates or aggregations.It is important to choose proper primary antibodies that are compatible with methanol and DCM treatment. New antibodies should be validated with small pieces of tissue or with methanol treated tissue sections. incubate the delipidated sample with the primary antibody solution for 3 to 5 days depending on the size of the sample.After the primary incubation wash the sample with several changes of PTXWH buffer. The next day, dilute the secondary antibody in PTXWH buffer to the recommended concentration. Centrifuge the diluted antibody solution as before.Incubate the sample with the secondary antibody solution for 3 to 5 days depending on the size of the sample. Again, wash the sample with PTXWH buffer in a series of incubation steps as before. The next day, wash the sample with 1XPBS for 5 minutes, 10 minutes, then 30 minutes.Embed Adipose Tissue in agarose to facilitate sample mounting for light sheet microscopy. First, prepare the embedding solution with 1 percent agarose in 1XPBS. Cool the embedding solution to around 40 degrees celsius to avoid exposing the sample to excessive heat.While avoiding liquid carryover, place the cleaned tissue sample into a mold and arrange it into the desired position. Then gently pour the embedding solution over the sample while avoiding air bubbles. Any air bubbles should be moved to the periphery before the agarose solidifies.Once the agarose has fully solidified, cut out a block containing the sample. Transfer the sample to 25 percent methanol in water, protect from light, and incubate with shaking for the time shown in table 2. Continue dehydrating the sample through a methanol gradient.Incubate the sample in 100 percent DCM for 1 hour with shaking. DCM Washed samples dry out easily in the air, which would affect the clearness of sample and result in blurry images. It is important to transfer samples quickly into fresh solution to prevent desiccation.The sample should sink to the bottom of the tube at the end of each DCM wash. Incubate the sample in Dibenzyl ether or DBE overnight with mild shaking to achieve refractive index matching. The sample will eventually become transparent, invisible light.The next day, after incubating the sample with fresh DBE with mild shaking for 2 hours, store the sample at room temperature in the dark or proceed directly to imaging. To image the sample with a light sheet microscope that is compatible with DBE, mount the agarose embedded sample onto a holder that can prevent movement during imaging. To image the sample with an inverted confocal or two-photon microscope place the agarose embedded sample into a chamber slide with a glass bottom.Scanning a posterior subcutantious fat pad using a light sheet microscope with low magnification shows the lobular organization of Adipocytes. More detailed information such as the size of the Adipocytes can be revealed by zooming into the regions of interest with higher magnification. A posterior subcutantious fat pad stained with Tyrosine Hydroxylase, a marker for the sympathetic nervous system was imaged by light sheet florescence microscopy.TH staining revealed structures that appear as large nerve bundles as indicated by the arrow here. Blood vessel innervation as well as dense terminal arborization in the tissue Parenchyma are also revealed by TH staining. Using platelet endothelial cell adhesion molecule or PCAM1 also known as CD31 as a marker to label blood vessels, it is observed that all Adipocytes are in contact with the capillaries throughout the whole tissue supporting the high demand for efficient nutrient and oxygen exchange in Adipose.After its development, this technique paved the way for researchers in the field of Adipose Biology to explore additional questions such as early tissue morphogenesis and fate mapping of Adipocyte Progenitors. It can also be applied to study the histology of human Adipose Tissue. Don't forget that working with paraformaldehyde, methanol, dichloromethane and Dibenzyl ether can be extremely hazardous and precautions such as using a fume hood and personal protective equipment should always be taken while performing this procedure.

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Research

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Biology

Actin Co-Sedimentation Assay; for the Analysis of Protein Binding to F-Actin

The actin cytoskeleton within the cell is a network of actin filaments that allows the movement of cells and cellular processes, and that generates tension and helps maintains cellular shape.  Although the actin cytoskeleton is a rigid structure, it is a dynamic structure that is constantly remodeling.  A number of proteins can bind to the actin cytoskeleton.  The binding of a particular protein to F-actin is often desired to support cell biological observations or to further understand dynamic processes due to remodeling of the actin cytoskeleton. The actin co-sedimentation assay is an in vitro assay routinely used to analyze the binding of specific proteins or protein domains with F-actin.  The basic principles of the assay involve an incubation of the protein of interest (full length or domain of) with F-actin, ultracentrifugation step to pellet F-actin and analysis of the protein co-sedimenting with F-actin.  Actin co-sedimentation assays can be designed accordingly to measure actin binding affinities and in competition assays.

Proteins bind to filamentous actin (F-actin) through distinct actin binding modules. In this video we demonstrate the procedure of actin co-sedimentation, which is an in vitro assay routinely used to analyze proteins or specific domains that bind F-actin.

The actin cytoskeleton within the cell is a network of actin filaments that allows the movement of cells and cellular processes, and that generates ...

Hi-C: A Method to Study the Three-dimensional Architecture of Genomes.

The three-dimensional folding of chromosomes compartmentalizes the genome and and can bring distant functional elements, such as promoters and enhancers, into close spatial proximity 2-6. Deciphering the relationship between chromosome organization and genome activity will aid in understanding genomic processes, like transcription and replication. However, little is known about how chromosomes fold. Microscopy is unable to distinguish large numbers of loci simultaneously or at high resolution. To date, the detection of chromosomal interactions using chromosome conformation capture (3C) and its subsequent adaptations required the choice of a set of target loci, making genome-wide studies impossible 7-10.
We developed Hi-C, an extension of 3C that is capable of identifying long range interactions in an unbiased, genome-wide fashion. In Hi-C, cells are fixed with formaldehyde, causing interacting loci to be bound to one another by means of covalent DNA-protein cross-links. When the DNA is subsequently fragmented with a restriction enzyme, these loci remain linked. A biotinylated residue is incorporated as the 5' overhangs are filled in. Next, blunt-end ligation is performed under dilute conditions that favor ligation events between cross-linked DNA fragments. This results in a genome-wide library of ligation products, corresponding to pairs of fragments that were originally in close proximity to each other in the nucleus. Each ligation product is marked with biotin at the site of the junction. The library is sheared, and the junctions are pulled-down with streptavidin beads. The purified junctions can subsequently be analyzed using a high-throughput sequencer, resulting in a catalog of interacting fragments.
Direct analysis of the resulting contact matrix reveals numerous features of genomic organization, such as the presence of chromosome territories and the preferential association of small gene-rich chromosomes. Correlation analysis can be applied to the contact matrix, demonstrating that the human genome is segregated into two compartments: a less densely packed compartment containing open, accessible, and active chromatin and a more dense compartment containing closed, inaccessible, and inactive chromatin regions. Finally, ensemble analysis of the contact matrix, coupled with theoretical derivations and computational simulations, revealed that at the megabase scale Hi-C reveals features consistent with a fractal globule conformation.

The Hi-C method allows unbiased, genome-wide identification of chromatin interactions (1). Hi-C couples proximity ligation and massively parallel sequencing. The resulting data can be used to study genomic architecture at multiple scales: initial results identified features such as chromosome territories, segregation of open and closed chromatin, and chromatin structure at the megabase scale.

The three-dimensional folding of chromosomes compartmentalizes the genome and and can bring distant functional elements, such as promoters and enhancers, ...

A System for Culturing Iris Pigment Epithelial Cells to Study Lens Regeneration in Newt

Salamanders like newt and axolotl possess the ability to regenerate many of its lost body parts such as limbs, the tail with spinal cord, eye, brain, heart, the jaw 1. Specifically, newts are unique for its lens regeneration capability. Upon lens removal, IPE cells of the dorsal iris transdifferentiate to lens cells and eventually form a new lens in about a month 2,3. This property of regeneration is never exhibited by the ventral iris cells. The regeneration potential of the iris cells can be studied by making transplants of the in vitro cultured IPE cells. For the culture, the dorsal and ventral iris cells are first isolated from the eye and cultured separately for a time period of 2 weeks (Figure 1). These cultured cells are reaggregated and implanted back to the newt eye. Past studies have shown that the dorsal reaggregate maintains its lens forming capacity whereas the ventral aggregate does not form a lens, recapitulating, thus the in vivo process (Figure 2) 4,5. This system of determining regeneration potential of dorsal and ventral iris cells is very useful in studying the role of genes and proteins involved in lens regeneration.

In newt, the lens regenerates always from the dorsal iris by transdifferentiation of the iris pigmented epithelial cells (IPEs). Here we describe a procedure to culture dorsal and ventral newt IPE cells and their implantation to the newt eye. The implanted cells are then studied by tissue sectioning and immunohistochemistry.

Salamanders like newt and axolotl possess the ability to regenerate many of its lost body parts such as limbs, the tail with spinal cord, eye, brain, ...

Quantitative Comparison of cis-Regulatory Element (CRE) Activities in Transgenic Drosophila melanogaster

Gene expression patterns are specified by cis-regulatory element (CRE) sequences, which are also called enhancers or cis-regulatory modules. A typical CRE possesses an arrangement of binding sites for several transcription factor proteins that confer a regulatory logic specifying when, where, and at what level the regulated gene(s) is expressed. The full set of CREs within an animal genome encodes the organism&prime;s program for development1, and empirical as well as theoretical studies indicate that mutations in CREs played a prominent role in morphological evolution2-4. Moreover, human genome wide association studies indicate that genetic variation in CREs contribute substantially to phenotypic variation5,6. Thus, understanding regulatory logic and how mutations affect such logic is a central goal of genetics. 
Reporter transgenes provide a powerful method to study the in vivo function of CREs. Here a known or suspected CRE sequence is coupled to heterologous promoter and coding sequences for a reporter gene encoding an easily observable protein product. When a reporter transgene is inserted into a host organism, the CRE&prime;s activity becomes visible in the form of the encoded reporter protein. P-element mediated transgenesis in the fruit fly species Drosophila (D.) melanogaster7 has been used for decades to introduce reporter transgenes into this model organism, though the genomic placement of transgenes is random. Hence, reporter gene activity is strongly influenced by the local chromatin and gene environment, limiting CRE comparisons to being qualitative. In recent years, the phiC31 based integration system was adapted for use in D. melanogaster to insert transgenes into specific genome landing sites8-10. This capability has made the quantitative measurement of gene and, relevant here, CRE activity11-13 feasible. The production of transgenic fruit flies can be outsourced, including phiC31-based integration, eliminating the need to purchase expensive equipment and/or have proficiency at specialized transgene injection protocols. 
Here, we present a general protocol to quantitatively evaluate a CRE&prime;s activity, and show how this approach can be used to measure the effects of an introduced mutation on a CRE&prime;s activity and to compare the activities of orthologous CREs. Although the examples given are for a CRE active during fruit fly metamorphosis, the approach can be applied to other developmental stages, fruit fly species, or model organisms. Ultimately, a more widespread use of this approach to study CREs should advance an understanding of regulatory logic and how logic can vary and evolve.

Quantitative Comparison of cis-Regulatory Element CRE Activities in Transgenic Drosophila melanogaster

Phenotypic variation for traits can result from mutations in cis-regulatory element (CRE) sequences that control gene expression patterns. Methods derived for use in Drosophila melanogaster can quantitatively compare the levels of spatial and temporal patterns of gene expression mediated by modified or naturally occurring CRE variants.

Gene expression patterns are specified by cis-regulatory element (CRE) sequences, which are also called enhancers or cis-regulatory modules. A typical CRE ...

FRET Imaging in Three-dimensional Hydrogels

Imaging of F&#246;rster resonance energy transfer (FRET)&#160;is a powerful tool for examining cell biology in real-time. Studies utilizing FRET commonly employ two-dimensional (2D) culture, which does not mimic the three-dimensional (3D) cellular microenvironment. A method to perform quenched emission FRET imaging using conventional widefield epifluorescence microscopy of cells within a 3D hydrogel environment is presented. Here an analysis method for ratiometric FRET probes that yields linear ratios over the probe activation range is described. Measurement of intracellular cyclic adenosine monophosphate (cAMP) levels is demonstrated in chondrocytes under forskolin stimulation using a probe for EPAC1 activation (ICUE1) and the ability to detect differences in cAMP signaling dependent on hydrogel material type, herein a photocrosslinking hydrogel (PC-gel, polyethylene glycol dimethacrylate) and a thermoresponsive hydrogel (TR-gel). Compared with 2D FRET methods, this method requires little additional work. Laboratories already utilizing FRET imaging in 2D can easily adopt this method to perform cellular studies in a 3D microenvironment. It can further be applied to high throughput drug screening in engineered 3D microtissues. Additionally, it is compatible with other forms of FRET imaging, such as anisotropy measurement and fluorescence lifetime imaging (FLIM), and with advanced microscopy platforms using confocal, pulsed, or modulated illumination.

F&#246;rster resonance energy transfer (FRET) imaging is a powerful tool for real-time cell biology studies. Here a method for FRET imaging cells in physiologic three-dimensional (3D) hydrogel microenvironments using conventional epifluorescence microscopy is presented. An analysis for ratiometric FRET probes that yields linear ratios over the activation range is described.

Imaging of F&#246;rster resonance energy transfer (FRET)&#160;is a powerful tool for examining cell biology in real-time. Studies utilizing FRET commonly ...

ACT-PRESTO: Biological Tissue Clearing and Immunolabeling Methods for Volume Imaging

The identification and exploration of the detailed organization of organs or of the whole body at the cellular level are fundamental challenges in biology. Transitional methods require a substantial amount of time and effort to obtain a 3D image and including sectioning the intact tissue, immunolabeling, and imaging serially-sectioned tissue, which produces a loss of information at each step of the process. In recently developed approaches for high-resolution imaging within intact tissue, molecular characterization has been restricted to the labeling of proteins. However, currently available protocols for organ clearing require a considerably long process time, making it difficult to implement tissue clearing techniques in the lab. We recently established a rapid and highly-reproducible protocol termed ACT-PRESTO (active clarity technique&#8211;pressure related efficient and stable transfer of macromolecules into organs), which allows for tissue clearance within several hours. Moreover, ACT-PRESTO enables rapid immunolabeling with conventional methods and accelerates antibody penetration into the deep layer of densely-formed, thick specimens by applying pressure or convection flow. We describe how to prepare tissues, how to clear by lipid removal using electrophoresis, and how to immuno-stain by a pressure-assisted delivery. The rapidity and consistency of the protocol will expedite the performance of 3D histological research and volume-based diagnoses.

ACT-PRESTO (active clarity technique&#8211;pressure related efficient and stable transfer of macromolecules into organs) enables rapid, efficient, but inexpensive tissue clearing and rapid antibody penetration into cleared tissues by passive diffusion or pressure-assisted delivery. Using this method, a wide range of tissues can be cleared, immunolabeled by multiple antibodies, and volume-imaged.

The identification and exploration of the detailed organization of organs or of the whole body at the cellular level are fundamental challenges in ...

Single-Cell Resolution Three-Dimensional Imaging of Intact Organoids

Organoid technology, in vitro 3D culturing of miniature tissue, has opened a new experimental window for cellular processes that govern organ development and function as well as disease. Fluorescence microscopy has played a major role in characterizing their cellular composition in detail and demonstrating their similarity to the tissue they originate from. In this article, we present a comprehensive protocol for high-resolution 3D imaging of whole organoids upon immunofluorescent labeling. This method is widely applicable for imaging of organoids differing in origin, size and shape. Thus far we have applied the method to airway, colon, kidney, and liver organoids derived from healthy human tissue, as well as human breast tumor organoids and mouse mammary gland organoids. We use an optical clearing agent, FUnGI, which enables the acquisition of whole 3D organoids with the opportunity for single-cell quantification of markers. This three-day protocol from organoid harvesting to image analysis is optimized for 3D imaging using confocal microscopy.

The entire 3D structure and cellular content of organoids, as well as their phenotypic resemblance to the original tissue can be captured using the single-cell resolution 3D imaging protocol described here. This protocol can be applied to a wide range of organoids varying in origin, size and shape.

Organoid technology, in vitro 3D culturing of miniature tissue, has opened a new experimental window for cellular processes that govern organ development ...

Exploring Adipose Tissue Structure by Methylsalicylate Clearing and 3D Imaging

Obesity is a major worldwide public health issue that increases the risk to develop cardiovascular diseases, type-2 diabetes, and liver diseases. Obesity is characterized by an increase in adipose tissue (AT) mass due to adipocyte hyperplasia and/or hypertrophia, leading to profound remodeling of its three-dimensional structure. Indeed, the maximal capacity of AT to expand during obesity is pivotal to the development of obesity-associated pathologies. This AT expansion is an important homeostatic mechanism to enable adaptation to an excess of energy intake and to avoid deleterious lipid spillover to other metabolic organs, such as muscle and liver. Therefore, understanding the structural remodeling that leads to the failure of AT expansion is a fundamental question with high clinical applicability. In this article, we describe a simple and fast clearing method that is routinely used in our laboratory to explore the morphology of mouse and human white adipose tissue by fluorescent imaging. This optimized AT clearing method is easily performed in any standard laboratory equipped with a chemical hood, a temperature-controlled orbital shaker and a fluorescent microscope. Moreover, the chemical compounds used are readily available. Importantly, this method allows one to resolve the 3D AT structure by staining various markers to specifically visualize the adipocytes, the neuronal and vascular networks, and the innate and adaptive immune cells distribution.

Here, we describe a simple, inexpensive and fast clearing method to resolve the 3D structure of both mouse and human white adipose tissue using a combination of markers to visualize vasculature, nuclei, immune cells, neurons, and lipid-droplet coat proteins by fluorescent imaging.

Obesity is a major worldwide public health issue that increases the risk to develop cardiovascular diseases, type-2 diabetes, and liver diseases. Obesity ...

Semi-Automated Isolation of Murine White Adipose Tissue

Semi-Automated Isolation of the Stromal Vascular Fraction from Murine White Adipose Tissue Using a Tissue Dissociator

The in vitro study of white, brown, and beige adipocyte differentiation enables the investigation of cell-autonomous functions of adipocytes and their mechanisms. Immortalized white preadipocyte cell lines are publicly available and widely used. However, the emergence of beige adipocytes in white adipose tissue in response to external cues is difficult to recapitulate to the full extent using publicly available white adipocyte cell lines. Isolation of the stromal vascular fraction (SVF) from murine adipose tissue is commonly executed to obtain primary preadipocytes and perform adipocyte differentiation. However, mincing and collagenase digestion of adipose tissue by hand can result in experimental variation and is prone to contamination. Here, we present a modified semi-automated protocol that utilizes a tissue dissociator for collagenase digestion to achieve easier isolation of the SVF, with the aim of reducing experimental variation, reducing contamination, and increasing reproducibility. The obtained preadipocytes and differentiated adipocytes can be used for functional and mechanistic analyses.

Author Spotlight: Semi-Automated Isolation of the Stromal Vascular Fraction from Murine White Adipose Tissue Using a Tissue Dissociator  

This protocol describes the semi-automated isolation of the stromal vascular fraction (SVF) from murine adipose tissue to obtain preadipocytes and achieve adipocyte differentiation in vitro. Using a tissue dissociator for collagenase digestion reduces experimental variation and increases reproducibility.

The in vitro study of white, brown, and beige adipocyte differentiation enables the investigation of cell-autonomous functions of adipocytes and their ...

Murine Adipose Tissue Excision

Shave the abdominal and inguinal regions of two sedated adult male Sprague Dawley rats. Disinfect the shaved regions with an iodine solution. Make a medial longitudinal incision from the sternum to the testicular region, Using a pair of sterile forceps, remove the adipose tissue from the epididymidis and the kidneys.Place the tissue in conical tubes containing 20 milliliters of cold, sterile PBS-AA solution.