Name: light-sheet fluorescence microscopy to capture 4-dimensional images of the effects of modulating shear stress on the developing zebrafish heart
Uploaded: 2018-08-10T14:30:00
Description: Watch this Scientific Journal Video about Light-sheet Fluorescence Microscopy to Capture 4-Dimensional Images of the Effects of Modulating Shear Stress on the Developing Zebrafish Heart at JoVE.com

The authors would like to express gratitude to William Talbot from Stanford University for providing the Human&#160;Nrg1&#160;cDNA and to Deborah Yelon from UCSD for providing the&#160;wea&#160;mutants. The authors would also like to thank Cynthia Chen for helping with image acquisition. This study was supported by grants NIH HL118650 (to T.K. Hsiai), HL083015 (to T.K. Hsiai), HD069305 (to N.C. Chi and T.K. Hsiai.), HL111437 (to T.K. Hsiai and N.C. Chi), HL129727 (to T.K. Hsiai), T32HL007895 (to R.R. Sevag Packard), HL 134613 (to V. Messerschmidt) and University of Texas System STARS funding (to J. Lee).

The following methods were performed in compliance with UTA and UCLA IACUC protocols. These experimental groups were used with transgenic Tg(cmlc2:gfp), the wea (weak atrium) or clo (cloche) mutants: (a) wild-type (WT) control, (b) gata1a MO, and (c) tnnt2a MO injections (Table 1).
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
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			<td>Model</td>
			<td>Name</td>
	...

<ol>
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In this protocol, we have shown that 4-D imaging can be used to track the development of a trabecular network in response to changes in biomechanical forces. In particular, the shear stress experienced by endothelial cells initiates the Notch signaling cascade, which in turn promotes trabeculation. In this manuscript, we have shown that (1) gata1a MO injection decreased hematopoiesis and therefore it reduced wall shear stress, (2) tnnt2a MO injection inhibited ventricular contractile function to reduce ...

An erratum was issued for:&#160;<a href="https://www.jove.com/video/57763/light-sheet-fluorescence-microscopy-to-capture-4-dimensional-images">Light-sheet Fluorescence Microscopy to Capture 4-Dimensional Images of the Effects of Modulating Shear Stress on the Developing Zebrafish Heart</a>.&#160;Additional author names were added, and an author affiliation was updated.
The author list was updated from:
Victoria Messerschmidt*1, Zachary Bailey*1, Kyung In Baek2, Richard Bryant1, Rongsong Li2, Tzung K. Hsiai2, Juhyun Lee1
to:
Victoria Messerschmidt*1, Zachary Bailey*1, Kyung In Baek2, Yichen Ding2, Jeffrey J. Hsu2, Richard Bryant1, Rongsong Li2, Tzung K. Hsiai2, Juhyun Lee1
The author affiliation for Rongsong Li was updated from:
Department of Medicine (Cardiology) and Bioengineering, UCLA
to:
College of Health Science and Environmental Engineering, Shenzhen Technology University

An erratum was issued for: <a href="https://www.jove.com/video/57763/light-sheet-fluorescence-microscopy-to-capture-4-dimensional-images">Light-sheet Fluorescence Microscopy to Capture 4-Dimensional Images of the Effects of Modulating Shear Stress on the Developing Zebrafish Heart</a>. Additional&#160;author names were&#160;added, and an author affiliation was updated.

Erratum: Light-sheet Fluorescence Microscopy to Capture 4-Dimensional Images of the Effects of Modulating Shear Stress on the Developing Zebrafish Heart

Biomechanical forces, such as hemodynamic shear stress, are intimately involved in cardiac morphogenesis. In response to hemodynamic shear forces, myocardial ridges and grooves develop in a wave-like trabecular network in alignment with the direction of the shear stress across the atrioventricular (AV) valve1. Cardiac trabeculation is necessary to increase contractile function and myocardial mass2. Mutations in Notch signaling pathways result in congenital heart defects in humans and other vertebrates3. For example, gata1a4 and tnnt2a5 morpholino oligonucleotides (MO) have been shown to reduce erythropoiesis, while erythropoietin mRNA (EPO)6 and Isoproterenol (ISO)7 increase red blood cells and heart rate respectively, and therefore wall shear stress (WSS). Furthermore, ErbB2 signaling, downstream of Notch, promotes cardiomyocyte proliferation and differentiation to generate contractile force, which in turn activates Notch signaling8,9. It is suggested that shear stress governs Notch signaling driven trabeculation for ventricular development. Currently, there are many studies that attempt to further understand the genetic programming events leading to congenital heart defects (CHD)10,11,12, but very little are investigating how mechanical forces influence the forming heart.
In order to investigate the mechanical forces acting on the endocardium, close observation during the developmental period needs to be implemented. However, it is challenging to obtain good quality images of in vivo beating samples due to the inherence of traditional microscopy13. In order to observe the development over time within a sample, physical sectioning and staining, therefore, need to occur13,14,15. Although confocal microscopy is widely used to image the 3-D structure of samples14,16, these imaging systems&#39; acquisition is still limited by slow scanning speeds.
Light-sheet fluorescence microscopy (LSFM) is a unique imaging technique that allows the visualization of in vivo dynamic events with long working distance13. This technique uses a light-sheet fluorescent microscopy to optically section a sample17. Due to illumination of only a thin sheet of light on the sample, there is a reduction in photo-bleaching and photo toxicity13,18. The large field of view and long working distance allows for large samples to stay intact as they are imaged13,14,17. The low magnification allows for a larger area to be imaged, while the long working distance allows for thicker samples to be imaged without compromising the signal-to-noise ratio. Many groups have used LSFM to image entire embryos17, brains14,18, muscles and hearts19 among other tissues, showing the diverse types of samples that can be imaged.
Although previous research demonstrated reduced hemodynamic shear force by occluding the inflow or outflow tracks of the zebrafish heart, the information is solely qualitative. It results in an abnormal third chamber, diminished cardiac looping, and impaired valve formation20. The 4-D LSFM images give a new perspective into the way the hemodynamic shear forces affect the development of the cardiac tissue. These mechanical forces may activate force-sensitive signaling molecules and induce the formation of the trabecular ridges. Because of the added time aspect of 4-D imaging, one is able to track changes in development in real time, which could lead to new revelations that had gone unnoticed previously. The zebrafish is an ideal model for imaging because scientists can observe an entire vertebrate animal versus only cell-cell interactions. Oxygen can also diffuse through the entire embryo, which allows development to occur without depending on the vascular system, unlike in mammalian development. Even though the zebrafish heart lacks the pulmonary organs, which require a four-chambered heart, there is a large number of cardiac genes that are conserved between zebrafish and humans21.
In this manuscript, we describe how to use light-sheet fluorescence microscopy to image the developing trabeculae in zebrafish hearts under various circumstances. First, injection of gata1a4 or tnnt2a5 MOs were used to lower the blood viscosity, and therefore WSS. The morphology of the heart was then recorded. In a separate group of fish, we increased the WSS by administering EPO mRNA6 or isoproterenol7 and observed the results. We also conducted a cell study with different pulsatile or oscillatory flow rates. After imaging each group, we found that WSS sensed by the endocardium via Notch signaling initiates trabeculation.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Clontech Hifi PCR pre-mix&#160;</td>
			<td>Takara&#160;</td>
			<td>639298</td>
			<td>PCR mastermix 
			1.1.1.1, 1.1.1.2, 1.1.1.5, 1.1.2.1, 3.1.4</td>
		</tr>
		<tr>
			<td>Human Nrg1 cDNA</td>
			<td>Gift from William Talbot, Stanford University, Stanford, California, USA</td>
			<td>N/A</td>
			<td>Used for trabeculation rescue 
			1.1.1.3, 1.1.1.4, 1.1.2.1</td>
		</tr>
		<tr>
			<td>CFX Connect&#8482; Real-Time PCR Detection System</td>
			<td>Bio-Rad</td>
			<td>1855201</td>
			<td>PCR Machine 
			1.1.1.5, 1.1.1.6, 1.1.2.2, 1.1.3.2</td>
		</tr>
		<tr>
			<td>pCS2+</td>
			<td>GE Health</td>
			<td></td>
			<td>Plasmid used to synthesize mRNA 
			1.1.2.1, 1.1.2.4, 1.1.2.5</td>
		</tr>
		<tr>
			<td>Nucleospin purification kit&#160;&#160;</td>
			<td>Clontech</td>
			<td>740609.25</td>
			<td>DNA Purification 
			1.1.2.3, 1.1.2.4, 1.1.6.2</td>
		</tr>
		<tr>
			<td>T4 DNA ligase&#160;</td>
			<td>Clontech</td>
			<td>2011A</td>
			<td>PCR Ligation solution 
			1.1.2.5</td>
		</tr>
		<tr>
			<td>Stellar competent cells</td>
			<td>Clontech</td>
			<td>636763</td>
			<td>E. coli cells used for transformation 
			1.1.2.6, 1.1.3.1, 1.1.3.2</td>
		</tr>
		<tr>
			<td>Lipofectamine 2000 transfection reagent</td>
			<td>Life Technologies</td>
			<td>11668027</td>
			<td>Transfection reagent 
			1.1.4</td>
		</tr>
		<tr>
			<td>mMessage SP6 kit</td>
			<td>Invitrogen</td>
			<td>AM1340</td>
			<td>Kit used to synthesize mRNA 
			1.1.6.3</td>
		</tr>
		<tr>
			<td>Aurum Total RNA Mini Kit</td>
			<td>Bio-Rad</td>
			<td>7326820</td>
			<td>Purifies RNA&#160; 
			1.1.6.4, 3.1.2</td>
		</tr>
		<tr>
			<td>GeneTools 4.3.8</td>
			<td>GeneTools</td>
			<td>N/A</td>
			<td>Software for primer design 
			1.2.1, 3.1.3</td>
		</tr>
		<tr>
			<td>EPO cDNA</td>
			<td>Creative Biogene</td>
			<td>CDFH006026</td>
			<td>Increases WSS 
			1.2.2, 1.2.3, 1.1.7</td>
		</tr>
		<tr>
			<td>AG1478</td>
			<td>Sigma-Aldrich&#160;</td>
			<td>T4182</td>
			<td>ErbB inhibitor 
			1.3.1</td>
		</tr>
		<tr>
			<td>E3 medium</td>
			<td></td>
			<td></td>
			<td>To grow embryos 
			1.3.1, 1.3.2, 5.1.5</td>
		</tr>
		<tr>
			<td>DAPT</td>
			<td>Sigma-Aldrich&#160;</td>
			<td>D5942</td>
			<td>&#947;-secretase inhibitor 
			1.3.2</td>
		</tr>
		<tr>
			<td>Agarose&#160;</td>
			<td>Sigma-Aldrich&#160;</td>
			<td>A9539</td>
			<td>Used for mounting embryos 
			2.1.1.1</td>
		</tr>
		<tr>
			<td>ORCA-Flash4.0 LT&#160;Digital CMOS camera</td>
			<td>Hamamatsu Photonics</td>
			<td>C11440-42U</td>
			<td>Used to capture Images 
			2.1.1.2, 2.1.1.3</td>
		</tr>
		<tr>
			<td>Amira Software</td>
			<td>FEI Software</td>
			<td>N/A</td>
			<td>Visualized and Analysed images into 3D, and 4D 
			2.1.5.1.1-2.1.5.2.8</td>
		</tr>
		<tr>
			<td>Tricaone mesylate&#160;</td>
			<td>Sigma-Aldrich&#160;</td>
			<td>886-86-2</td>
			<td>Used to humanely sedated or sacrifice embryos 
			3.1.1</td>
		</tr>
		<tr>
			<td>iScript cDNA Synthesis Kit</td>
			<td>Bio-Rad</td>
			<td>1708890</td>
			<td>Synthesizes cDNA 
			3.1.2</td>
		</tr>
		<tr>
			<td>Eppendorf 5424 microcentrifuge</td>
			<td>Eppendorf</td>
			<td>05-400-005</td>
			<td>Microcentrifuge 
			4.1.1.3</td>
		</tr>
		<tr>
			<td>GI254023X</td>
			<td>Sigma-Aldrich&#160;</td>
			<td>260264-93-5</td>
			<td>ADAM10 inhibitor 
			4.1.2, 4.1.3&#160;</td>
		</tr>
		<tr>
			<td>Isoprenaline hydrochloride</td>
			<td>Sigma-Aldrich&#160;</td>
			<td>I5627</td>
			<td>Isoproterenol increases WSS 
			5.1.5</td>
		</tr>
		<tr>
			<td>MATLAB</td>
			<td>Mathworks</td>
			<td>N/A</td>
			<td>Cardiac mechanics analysis</td>
		</tr>
	</tbody>
</table>

light-sheet fluorescence microscopy to capture 4-dimensional images of the effects of modulating shear stress on the developing zebrafish heart

The hemodynamic forces experienced by the heart influence cardiac development, especially trabeculation, which forms a network of branching outgrowths from the myocardium. Genetic program defects in the Notch signaling cascade are involved in ventricular defects such as Left Ventricular Non-Compaction Cardiomyopathy or Hypoplastic Left Heart Syndrome. Using this protocol, it can be determined that shear stress driven trabeculation and Notch signaling are related to one another. Using Light-sheet Fluorescence Microscopy, visualization of the developing zebrafish heart was possible. In this manuscript, it was assessed whether hemodynamic forces modulate the initiation of trabeculation via Notch signaling and thus, influence contractile function occurs. For qualitative and quantitative shear stress analysis, 4-D (3-D+time) images were acquired during zebrafish cardiac morphogenesis, and integrated light-sheet fluorescence microscopy with 4-D synchronization captured the ventricular motion. Blood viscosity was reduced via gata1a-morpholino oligonucleotides (MO) micro-injection to decrease shear stress, thereby, down-regulating Notch signaling and attenuating trabeculation. Co-injection of Nrg1 mRNA with gata1a MO rescued Notch-related genes to restore trabeculation. To confirm shear stress driven Notch signaling influences trabeculation, cardiomyocyte contraction was further arrested via tnnt2a-MO to reduce hemodynamic forces, thereby, down-regulating Notch target genes to develop a non-trabeculated myocardium. Finally, corroboration of the expression patterns of shear stress-responsive Notch genes was conducted by subjecting endothelial cells to pulsatile flow. Thus, the 4-D light-sheet microscopy uncovered hemodynamic forces underlying Notch signaling and trabeculation with clinical relevance to non-compaction cardiomyopathy.

LSFM was used in this manuscript in order to acquire high-resolution 2-D and 3-D pictures. As seen in Figure 1A and 1B, the illumination lens directs the light sheet at the sample. Because of the thinness of the light sheet, only a single plane is illuminated. The detection lens is positioned perpendicular to the illumination lens and is focused on the illuminated plane (Figure 1B). The light sheet from the illum...

Watch this Scientific Journal Video about Light-sheet Fluorescence Microscopy to Capture 4-Dimensional Images of the Effects of Modulating Shear Stress on the Developing Zebrafish Heart at JoVE.com

Light-sheet Fluorescence Microscopy to Capture 4-Dimensional Images of the Effects of Modulating Shear Stress on the Developing Zebrafish Heart

Here, we present a protocol to visualize developing hearts in zebrafish in 4-Dimensions (4-D). 4-D imaging, via light-sheet fluorescence microscopy (LSFM), takes 3-Dimensional (3-D) images over time, to reconstruct developing hearts. We show qualitatively and quantitatively that shear stress activates endocardial Notch signaling during chamber development, which promotes cardiac trabeculation.

The hemodynamic forces experienced by the heart influence cardiac development, especially trabeculation, which forms a network of branching outgrowths ...

This method can help answer key questions in the developmental cardiac mechanobiology field, such as the modulation of shear stress on cardiac trabeculation via notch signaling using a 4D light sheet microscope. The main advantage of this technique is that it illuminates a thin section of sample with a five micron plane, leading to less photo bleaching and photo damage. In addition, our computational algorithm allows us to reconstruct a 4D beating zebrafish heart.The implications of this technique extend toward the diagnosis of congenital cardiac diseases as it allows for the invivo sequential visualization of the cardiac trabeculation in an early developmental stage on through to the later phenotype. Generally, people who are new to this technique will find that thinking in three dimensions over time is difficult to imagine. In addition, it takes time to create the system and accurately align it.To begin, separate the male and female zebrafish in the the breeding tanks by using a divider. Then, lift the divider and allow the male and female zebrafish to breed. Collect the zebrafish embryos and inject morpholino oligo into the embryo to inhibit trabeculation.Next, prepare a one percent agarose gel by adding one gram of agarose to 100 milliliters of distilled water and heat it until all of the agarose is dissolved. Allow the agarose to cool and then use a 20 microliter pipet to load a small plastic tube with one of the prepared embryos and agarose. Secure the tube onto the microscope stage and use the ten x objective.Adjust the objective using the knob so that the top of the embryo is in focus. Take images of the entire fish embryo over multiple cardiac beating cycles using a light sheet thickness of five microns. Collect 500 xy frames with an exposure time of ten milliseconds.Then, move the stage one micron in the z access to a new layer and repeat the imaging procedure. Continue imagine 500 frames per z plane until the entire heart is fully imaged. Next, open the image processing software and begin to stack the images into 3D.To accomplish this, first click on open data. Here, select all of the images that are to be stacked into 3D and then select load. Then add in the voxel size of 0.65 by 0.65 by one micron and click on okay.Inputting the correct voxel size is critical for accurate analysis of the 3D images. Now, click on the multiplaner viewbox and visualize the 3D image. Right-click the blue slice one dot tiff box, select display, and then click on volran.In the edit menu, select options, and then edit color map. Adjust the color using the boxes and then click on okay. While still in the image processing software, click on file, and open the time series data.Select the 3D tiffs that were just made by clicking on load, and enter the same voxel size as before. Right-click the blue slice one dot tiff box, and then select display followed by volran. Now, click on edit.Select options. And then select edit color map. Adjust the color using the boxes and then click on okay.Next, right-click on the time series control, click movie maker, and press the play button in order to watch the movie. To finish up, add a file name, frame size, frame rate, quality equal to one, and enter monoscopic. Then click apply.Finally, export the video. Biomechanical forces, such as hemodynamic shear stress, are intimately involved in cardiac morphogenesis. Here, light sheet fluorescence microscopy was used to visualize the trabecular ridges protruding into the ventricular lumen at 75 hours post fertilization.At 100 hours post fertilization a trabecular network can clearly be seen. In an embryo treated with the gata1aMO microinjection, hematopoiesis and viscosity are reduced by 90 percent. This decreased viscosity attenuated hemodynamic shear stress, resulting in a delayed initiation and a less dense trabecular network.This delay and density of the trabecular network was able to be recovered by up regulating notch related gene expression, rescuing trabecular formation at 75 hours post fertilization and at 100 hours post fertilization. Thus, gata1a morpholino oligonucleotides reduced hemodynamic forces leading to down regulation of notch signaling, whereas Nrg1-mRNA rescue up regulated notch related genes and reinitiated trabeculation. Once mastered, this imaging technique can be completed in approximately two hours if performed properly.After its development, this technique paved the way for researchers in the field of cardiac development to study the factors in the notch gene, which are responsible for the proper formation of trabeculation in zebrafish. After watching this video, you should have a good understanding of how to acquire images using selective plane illumination microscopy and create 4D image files. Don't forget that working with lasers can be extremely hazardous.And precautions, such as wearing appropriate eyewear, should always be taken during this procedure.

light-sheet-fluorescence-microscopy-to-capture-4-dimensional-images

Research

JoVE Journal

Bioengineering

Design of a Cyclic Pressure Bioreactor for the Ex Vivo Study of Aortic Heart Valves

The aortic valve, located between the left ventricle and the aorta, allows for unidirectional blood flow, preventing backflow into the ventricle. Aortic valve leaflets are composed of interstitial cells suspended within an extracellular matrix (ECM) and are lined with an endothelial cell monolayer. The valve withstands a harsh, dynamic environment and is constantly exposed to shear, flexion, tension, and compression. Research has shown calcific lesions in diseased valves occur in areas of high mechanical stress as a result of endothelial disruption or interstitial matrix damage1-3. Hence, it is not surprising that epidemiological studies have shown high blood pressure to be a leading risk factor in the onset of aortic valve disease4. 
The only treatment option currently available for valve disease is surgical replacement of the diseased valve with a bioprosthetic or mechanical valve5. Improved understanding of valve biology in response to physical stresses would help elucidate the mechanisms of valve pathogenesis. In turn, this could help in the development of non-invasive therapies such as pharmaceutical intervention or prevention. Several bioreactors have been previously developed to study the mechanobiology of native or engineered heart valves6-9. Pulsatile bioreactors have also been developed to study a range of tissues including cartilage10, bone11 and bladder12. The aim of this work was to develop a cyclic pressure system that could be used to elucidate the biological response of aortic valve leaflets to increased pressure loads. 
The system consisted of an acrylic chamber in which to place samples and produce cyclic pressure, viton diaphragm solenoid valves to control the timing of the pressure cycle, and a computer to control electrical devices. The pressure was monitored using a pressure transducer, and the signal was conditioned using a load cell conditioner. A LabVIEW program regulated the pressure using an analog device to pump compressed air into the system at the appropriate rate. The system mimicked the dynamic transvalvular pressure levels associated with the aortic valve; a saw tooth wave produced a gradual increase in pressure, typical of the transvalvular pressure gradient that is present across the valve during diastole, followed by a sharp pressure drop depicting valve opening in systole. The LabVIEW program allowed users to control the magnitude and frequency of cyclic pressure. The system was able to subject tissue samples to physiological and pathological pressure conditions. This device can be used to increase our understanding of how heart valves respond to changes in the local mechanical environment.

Design of a Cyclic Pressure Bioreactor for the Ex Vivo Study of Aortic Heart Valves

A cyclic pressure bioreactor capable of subjecting heart valve tissue to physiological and pathological pressure conditions has been designed. A LabVIEW program allows users to control pressure magnitude, amplitude and frequency. This device can be used to study the mechanobiology of heart valve tissue or isolated cells.

The aortic valve, located between the left ventricle and the aorta, allows for unidirectional blood flow, preventing backflow into the ventricle. Aortic ...

Low Molecular Weight Protein Enrichment on Mesoporous Silica Thin Films for Biomarker Discovery

The identification of circulating biomarkers holds great potential for non invasive approaches in early diagnosis and prognosis, as well as for the monitoring of therapeutic efficiency.1-3 The circulating low molecular weight proteome (LMWP) composed of small proteins shed from tissues and cells or peptide fragments derived from the proteolytic degradation of larger proteins, has been associated with the pathological condition in patients and likely reflects the state of disease.4,5 Despite these potential clinical applications, the use of Mass Spectrometry (MS) to profile the LMWP from biological fluids has proven to be very challenging due to the large dynamic range of protein and peptide concentrations in serum.6 Without sample pre-treatment, some of the more highly abundant proteins obscure the detection of low-abundance species in serum/plasma. Current proteomic-based approaches, such as two-dimensional polyacrylamide gel-electrophoresis (2D-PAGE) and shotgun proteomics methods are labor-intensive, low throughput and offer limited suitability for clinical applications.7-9 Therefore, a more effective strategy is needed to isolate LMWP from blood and allow the high throughput screening of clinical samples. 
Here, we present a fast, efficient and reliable multi-fractionation system based on mesoporous silica chips to specifically target and enrich LMWP.10,11 Mesoporous silica (MPS) thin films with tunable features at the nanoscale were fabricated using the triblock copolymer template pathway. Using different polymer templates and polymer concentrations in the precursor solution, various pore size distributions, pore structures, connectivity and surface properties were determined and applied for selective recovery of low mass proteins. The selective parsing of the enriched peptides into different subclasses according to their physicochemical properties will enhance the efficiency of recovery and detection of low abundance species. In combination with mass spectrometry and statistic analysis, we demonstrated the correlation between the nanophase characteristics of the mesoporous silica thin films and the specificity and efficacy of low mass proteome harvesting. The results presented herein reveal the potential of the nanotechnology-based technology to provide a powerful alternative to conventional methods for LMWP harvesting from complex biological fluids. Because of the ability to tune the material properties, the capability for low-cost production, the simplicity and rapidity of sample collection, and the greatly reduced sample requirements for analysis, this novel nanotechnology will substantially impact the field of proteomic biomarker research and clinical proteomic assessment.

We developed a technology based on mesoporous silica thin film for the selective recovery of low molecular weight proteins and peptides from human serum. The physico-chemical properties of our mesoporous chips were finely tuned to provide substantial control in peptide enrichment and consequently profile the serum proteome for diagnostic purposes.

The identification of circulating biomarkers holds great potential for non invasive approaches in early diagnosis and prognosis, as well as for the ...

3D Orbital Tracking in a Modified Two-photon Microscope: An Application to the Tracking of Intracellular Vesicles

The objective of this video protocol is to discuss how to perform and analyze a three-dimensional fluorescent orbital particle tracking experiment using a modified two-photon microscope1. As opposed to conventional approaches (raster scan or wide field based on a stack of frames), the 3D orbital tracking allows to localize and follow with a high spatial (10 nm accuracy) and temporal resolution (50 Hz frequency response) the 3D displacement of a moving fluorescent particle on length-scales of hundreds of microns2. The method is based on a feedback algorithm that controls the hardware of a two-photon laser scanning microscope in order to perform a circular orbit around the object to be tracked: the feedback mechanism will maintain the fluorescent object in the center by controlling the displacement of the scanning beam3-5. To demonstrate the advantages of this technique, we followed a fast moving organelle, the lysosome, within a living cell6,7. Cells were plated according to standard protocols, and stained using a commercially lysosome dye. We discuss briefly the hardware configuration and in more detail the control software, to perform a 3D orbital tracking experiment inside living cells. We discuss in detail the parameters required in order to control the scanning microscope and enable the motion of the beam in a closed orbit around the particle. We conclude by demonstrating how this method can be effectively used to track the fast motion of a labeled lysosome along microtubules in 3D within a live cell. Lysosomes can move with speeds in the range of 0.4-0.5 &#181;m/sec, typically displaying a directed motion along the microtubule network8.

In this video protocol we track - at high speed and in three dimensions - fluorescently labeled lysosomes within living cells, using the orbital tracking method in a modified two-photon microscope.

The objective of this video protocol is to discuss how to perform and analyze a three-dimensional fluorescent orbital particle tracking experiment using a ...

Light-sheet Fluorescence Microscopy for the Study of the Murine Heart

Light-sheet fluorescence microscopy has been widely used for rapid image acquisition with a high axial resolution from micrometer to millimeter scale. Traditional light-sheet techniques involve the use of a single illumination beam directed orthogonally at sample tissue. Images of large samples that are produced using a single illumination beam contain stripes or artifacts and suffer from a reduced resolution due to the scattering and absorption of light by the tissue. This study uses a dual-sided illumination beam and a simplified CLARITY optical clearing technique for the murine heart. These techniques allow for deeper imaging by removing lipids from the heart and produce a large field of imaging, greater than 10 x 10 x 10 mm3. As a result, this strategy enables us to quantify the ventricular dimensions, track the cardiac lineage, and localize the spatial distribution of cardiac-specific proteins and ion-channels from the post-natal to adult mouse hearts with sufficient contrast and resolution.

This study uses a dual-sided illumination light-sheet fluorescence microscopy (LSFM) technique combined with optical clearing to study the murine heart.

Light-sheet fluorescence microscopy has been widely used for rapid image acquisition with a high axial resolution from micrometer to millimeter scale. ...

Gene Expression Analysis of Endothelial Cells Exposed to Shear Stress Using Multiple Parallel-plate Flow Chambers

We describe a workflow for the analysis of gene expression from endothelial cells subject to a steady laminar flow using multiple monitored parallel-plate flow chambers. Endothelial cells form the inner cellular lining of blood vessels and are chronically exposed to the frictional force of blood flow called shear stress. Under physiological conditions, endothelial cells function in the presence of various shear stress conditions. Thus, the application of shear stress conditions in in vitro models can provide greater insight into endothelial responses in vivo. The parallel-plate flow chamber previously published by Lane et al.9 is adapted to study endothelial gene regulation in the presence and absence of steady (non-pulsatile) laminar flow. Key adaptations in the set-up for laminar flow as presented here include a large, dedicated environment to house concurrent flow circuits, the monitoring of flow rates in real-time, and the inclusion of an exogenous reference RNA for the normalization of quantitative real-time PCR data. To assess multiple treatments/conditions with the application of shear stress, multiple flow circuits and pumps are used simultaneously within the same heated and humidified incubator. The flow rate of each flow circuit is measured continuously in real-time to standardize shear stress conditions throughout the experiments. Because these experiments have multiple conditions, we also use an exogenous reference RNA that is spiked-in at the time of RNA extraction for the normalization of RNA extraction and first-strand cDNA synthesis efficiencies. These steps minimize the variability between samples. This strategy is employed in our pipeline for the gene expression analysis with shear stress experiments using the parallel-plate flow chamber, but parts of this strategy, such as the exogenous reference RNA spike-in, can easily and cost-effectively be used for other applications.

Here, a workflow for the culture and gene expression analysis of endothelial cells under fluid shear stress is presented. Included is a physical arrangement for simultaneously housing and monitoring multiple flow chambers in a controlled environment and the use of an exogenous reference RNA for quantitative PCR.

We describe a workflow for the analysis of gene expression from endothelial cells subject to a steady laminar flow using multiple monitored parallel-plate ...

Live Cell Analysis of Shear Stress on Pseudomonas aeruginosa Using an Automated Higher-Throughput Microfluidic System

A higher-throughput microfluidic in vitro bioreactor coupled with fluorescence microscopy has been used to study bacterial biofilm growth and morphology, including Pseudomonas aeruginosa (P. aeruginosa). Here, we will describe how the system can be used to study the growth kinetics and the morphological properties such as the surface roughness and textural entropy of P. aeruginosa strain PA01 that expresses an enhanced green fluorescent protein (PA01-EGFP). A detailed protocol will describe how to grow and seed PA01-EGFP cultures, how to set up the microscope and autorun, and conduct the image analysis to determine growth rate and morphological properties using a variety of shear forces that are controlled by the microfluidic device. This article will provide a detailed description of a technique to improve the study of PA01-EGFP biofilms which eventually can be applied towards other strains of bacteria, fungi, or algae biofilms using the microfluidic platform.

Live Cell Analysis of Shear Stress on Pseudomonas aeruginosa Using an Automated Higher-Throughput Microfluidic System

Here, we describe the use of a higher-throughput microfluidic bioreactor coupled with a fluorescent microscope for the analysis of shear stress effects on Pseudomonas aeruginosa biofilms expressing green fluorescent proteins, including instrument set up, the determination of biofilm coverage, growth rate, and morphological properties.

A higher-throughput microfluidic in vitro bioreactor coupled with fluorescence microscopy has been used to study bacterial biofilm growth and morphology, ...

Characterizing Single-Molecule Conformational Changes Under Shear Flow with Fluorescence Microscopy

Single-molecule behavior under mechanical perturbation has been characterized widely to understand many biological processes. However, methods such as atomic force microscopy have limited temporal resolution, while F&#246;rster resonance energy transfer (FRET) only allow conformations to be inferred. Fluorescence microscopy, on the other hand, allows real-time in situ visualization of single molecules in various flow conditions. Our protocol describes the steps to capture conformational changes of single biomolecules under different shear flow environments using fluorescence microscopy. The shear flow is created inside microfluidic channels and controlled by a syringe pump. As demonstrations of the method, von Willebrand factor (VWF) and lambda DNA are labeled with biotin and fluorophore and then immobilized on the channel surface. Their conformations are continuously monitored under variable shear flow using total internal reflection (TIRF) and confocal fluorescence microscopy. The reversible unraveling dynamics of VWF are useful for understanding how its function is regulated in human blood, while the conformation of lambda DNA offers insights into the biophysics of macromolecules. The protocol can also be widely applied to study the behavior of polymers, especially biopolymers, in varying flow conditions and to investigate the rheology of complex fluids.

We present a protocol for immobilizing single macromolecules in microfluidic devices and quantifying changes in their conformations under shear flow. This protocol is useful for characterizing the biomechanical and functional properties of biomolecules such as proteins and DNA in a flow environment.

Single-molecule behavior under mechanical perturbation has been characterized widely to understand many biological processes. However, methods such as ...

Analysis of Zebrafish Cardiac Contraction with Virtual Reality Interaction

4D Light-sheet Imaging of Zebrafish Cardiac Contraction

Zebrafish is an intriguing model organism known for its remarkable cardiac regeneration capacity. Studying the contracting heart in vivo is essential for gaining insights into structural and functional changes in response to injuries. However, obtaining high-resolution and high-speed 4-dimensional (4D, 3D spatial + 1D temporal) images of the zebrafish heart to assess cardiac architecture and contractility remains challenging. In this context, an in-house light-sheet microscope (LSM) and customized computational analysis are&#160;used to overcome these technical limitations. This strategy, involving LSM system construction, retrospective synchronization, single cell tracking, and user-directed analysis, enables one to investigate the micro-structure and contractile function across the entire heart at the single-cell resolution in the transgenic Tg(myl7:nucGFP) zebrafish larvae. Additionally, we are able to further incorporate microinjection of small molecule compounds to induce cardiac injury in a precise and controlled manner. Overall, this framework allows one to track physiological and pathophysiological changes, as well as the regional mechanics at the single-cell level during cardiac morphogenesis and regeneration.

Author Spotlight: High-Resolution 4D Light-Sheet Imaging and Virtual Reality in Zebrafish for Single-Cell Analysis of Heart Function

This protocol utilizes light-sheet imaging to investigate cardiac contractile function in zebrafish larvae and gain insights into cardiac mechanics through cell tracking and interactive analysis.

Zebrafish is an intriguing model organism known for its remarkable cardiac regeneration capacity. Studying the contracting heart in vivo is essential for ...

Light-Sheet Microscopy and Tissue Clearing for Comprehensive Cardiac Imaging

Light-Sheet Imaging to Reveal Cardiac Structure in Rodent Hearts

Light-sheet microscopy (LSM) plays a pivotal role in comprehending the intricate three-dimensional (3D) structure of the heart, providing crucial insights into fundamental cardiac physiology and pathologic responses. We hereby delve into the development and implementation of the LSM technique to elucidate the micro-architecture of the heart in mouse models. The methodology integrates a customized LSM system with tissue clearing techniques, mitigating light scattering within cardiac tissues for volumetric imaging. The combination of conventional LSM with image stitching and multiview deconvolution approaches allows for the capture of the entire heart. To address the inherent trade-off between axial resolution and field of view (FOV), we further introduce an axially swept light-sheet microscopy (ASLM) method to minimize out-of-focus light and uniformly illuminate the heart across the propagation direction. In the meanwhile, tissue clearing methods such as iDISCO enhance light penetration, facilitating the visualization of deep structures and ensuring a comprehensive examination of the myocardium throughout the entire heart. The combination of the proposed LSM and tissue clearing methods presents a promising platform for researchers in resolving cardiac structures in rodent hearts, holding great potential for the understanding of cardiac morphogenesis and remodeling.

Author Spotlight: Customized Light-Sheet Imaging for Investigating Myocardial Structures in Rodent Hearts

The protocol utilizes advanced light-sheet microscopy along with adapted tissue clearing methods to investigate intricate cardiac structures in rodent hearts, holding great potential for the understanding of cardiac morphogenesis and remodeling.

Light-sheet microscopy (LSM) plays a pivotal role in comprehending the intricate three-dimensional (3D) structure of the heart, providing crucial insights ...