Name: high-fat feeding paradigm for larval zebrafish: feeding, live imaging, and quantification of food intake
Uploaded: 2016-10-27T15:00:00
Description: Watch this Scientific Journal Video about High-fat Feeding Paradigm for Larval Zebrafish: Feeding, Live Imaging, and Quantification of Food Intake at JoVE.com

The authors thank Meng-Chieh Shen for images, Jennifer Anderson for providing helpful comments on the manuscript, and members of the Farber laboratory for their contributions in developing these techniques. This study was funded by NIDDK-NIH award RO1DK093399 (S.A.F.), RO1GM63904 (The Zebrafish Functional Genomics Consortium: PI Stephen Ekker and Co-PI S.A.F), and F32DK096786 (J.P.O.). This content is solely the responsibility of the authors and does not necessarily represent the official views of NIH. Additional support was provided by the G. Harold and Leila Y. Mathers Charitable Foundation to the laboratory of S.A.F and the Carnegie Institution for Science endowment.

These protocols have been approved by the Carnegie Institution for Science Institutional Animal Care and Use Committee (protocol no. 139).
1. Animal Preparation
<ol>
	<li>Maintain adults and larvae at 28 &#176;C on a 14 hr:10 hr light:dark cycle. Feed adults twice daily with shell free Artemia (decapsulated, non-hatching, starting at 14 dpf) and commercial micropellets.</li>
	<li>These protocols are optimized for the use of 6-7 dpf larvae collected by natural spawning of the AB background. Protocols can...

<ol>
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C., Amsterdam, A., Soroka, C., Boyer, J., Hopkins, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+genetic+screen+in+zebrafish+identifies+the+mutants+vps18,+nf2+and+foie+gras+as+models+of+liver+disease.">A genetic screen in zebrafish identifies the mutants vps18, nf2 and foie gras as models of liver disease.</a> Development. 132 (15), 3561-3572 (2005).</li><li>Matthews, R. 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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=Overexpression+of+Akt1+enhances+adipogenesis+and+leads+to+lipoma+formation+in+zebrafish.">Overexpression of Akt1 enhances adipogenesis and leads to lipoma formation in zebrafish.</a> PLoS One. 7 (5), 36474 (2012).</li><li>Song, Y., Cone, R. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Creation+of+a+genetic+model+of+obesity+in+a+teleost.">Creation of a genetic model of obesity in a teleost.</a> FASEB J. 21 (9), 2042-2049 (2007).</li><li>Watts, S. A., Powell, M., D'Abramo, L. 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The techniques described here allow researchers to treat larval zebrafish with a lipid-rich feed, visualize dietary lipid processing in live larvae, and quantify larval food intake. To ensure success, special attention should be given to several critical steps. Commercial chicken eggs vary; to minimize potential variability we perform all assays on organic eggs from cage-free chickens that have not been enriched for omega-3 fatty acids. Lower feeding rates may be observed in fish younger than 6 dpf with remaining endogen...

The mechanisms by which the intestine regulates dietary lipid processing, the liver controls complex lipid synthesis and lipoprotein metabolism, and how these organs work with the central nervous system to control food intake are incompletely understood. It is of biomedical interest to elucidate this biology in light of the current epidemics of obesity, cardiovascular disease, diabetes, and non-alcoholic fatty liver disease. Studies in cell culture and mice have provided the majority of our understanding of the mechanistic relationships between dietary lipids and disease, and zebrafish (Danio rerio) are emerging as an ideal model to complement this work.
Zebrafish have similar gastrointestinal (GI) organs, lipid metabolism, and lipoprotein transport to higher vertebrates 1,2, develop rapidly, and are genetically tractable. The optical clarity of the larval zebrafish facilitates in vivo studies, a particular advantage for study of the GI system as its extracellular milieu (i.e., bile, microbiota, endocrine signaling) is virtually impossible to model ex vivo. In accordance, a body of research combining the genetic tractability and conduciveness to live imaging of zebrafish larvae with a variety of dietary manipulations (high-fat3,4, -cholesterol5, and -carbohydrate diets6,7), and models of cardiovascular disease8, diabetes9,10, hepatic steatosis11-13, and obesity14-16, are emerging to provide a host of metabolic insights.
An essential aspect of transitioning the larval zebrafish into metabolic research is the optimization of techniques developed in other model animals to the zebrafish and the development of novel assays that exploit the unique strengths of the zebrafish. This protocol presents techniques developed and optimized to feed larval zebrafish a lipid-rich meal, visualize dietary lipid processing from whole body to subcellular resolution, and measure food intake. Chicken egg yolk was chosen to compose the lipid-rich meal as it contains high levels of fats and cholesterol (lipids compose ~58% of chicken egg yolk, of which ~5% is cholesterol, 60% are triglycerides, and 35% are phospholipids). Chicken egg yolk provides more fat than typical commercial zebrafish micropellet foods (~15% lipids) and the advantage that it is a standardized feed with known percentages of specific fatty acids species, as zebrafish diets and feeding regiments have not been standardized across labs17. Moreover, fluorescent lipid analogs provided in the egg yolk visualize transport and accumulation of dietary lipids18, image cellular components including lipid droplets by acting both as vital dyes3 and through covalent incorporation into complex lipids, investigate metabolism through thin layer chromatography (TLC)19 and high performance liquid chromatography (HPLC) (S.A.F. unpublished data), and provide a quantitative assay for total food intake20.

<table border="0" cellpadding="0" cellspacing="0" width="832">
	<tbody>
		<tr height="40">
			<td height="40" style="height:40px;width:231px;">Tricaine (ethyl 3-aminobenzoate methanesulofnate salt)</td>
			<td style="width:143px;">Sigma-Aldrich</td>
			<td style="width:127px;">A5040-25G</td>
			<td style="width:335px;">Anesthesia for larval zebrafish</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:231px;">Chicken eggs</td>
			<td style="width:143px;">N/A</td>
			<td style="width:127px;">N/A</td>
			<td>Organic, cage-free eggs, not enriched for omege-3 fatty acids</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:231px;">Ultrasonic processor 3000 sonicator</td>
			<td style="width:143px;">Misonix, Inc.</td>
			<td style="width:127px;">S-3000</td>
			<td>To make egg yolk liposomes</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:231px;">Sonabox acoustic enclosure</td>
			<td style="width:143px;">Misonix, Inc.</td>
			<td style="width:127px;">432B</td>
			<td>To make egg yolk liposomes</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:231px;">1/8&#8221; tapered microtip</td>
			<td style="width:143px;">Misonix, Inc.</td>
			<td style="width:127px;">419</td>
			<td>To make egg yolk liposomes</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:231px;">Amber vials (4 ml, glass)</td>
			<td style="width:143px;">National Scientific</td>
			<td style="width:127px;">13-425</td>
			<td>Lipid storage; includes vials, open-top caps, and cap septa</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:231px;">Incu-Shaker Mini&#160;</td>
			<td style="width:143px;">Benchmark</td>
			<td style="width:127px;">1222U12</td>
			<td>Incubated shaker for feeds</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:231px;">BODIPY FL C16&#160;</td>
			<td style="width:143px;">Thermo Fisher Scientific</td>
			<td style="width:127px;">D3821</td>
			<td>Fluorescent lipid analog; (4,4-Difluoro-5,7-Dimethyl-4-Bora-3a,4a-Diaza-s-Indacene-3-Hexadecanoic Acid)</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:231px;">BODIPY FL C12&#160;</td>
			<td style="width:143px;">Thermo Fisher Scientific</td>
			<td style="width:127px;">D3822</td>
			<td>Fluorescent lipid analog; (4,4-Difluoro-5,7-Dimethyl-4-Bora-3a,4a-Diaza-s-Indacene-3-Dodecanoic Acid)</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:231px;">BODIPY FL C5&#160;</td>
			<td style="width:143px;">Thermo Fisher Scientific</td>
			<td style="width:127px;">D3834</td>
			<td>Fluorescent lipid analog; (4,4-Difluoro-5,7-Dimethyl-4-Bora-3a,4a-Diaza-s-Indacene-3-Pentanoic Acid)</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:231px;">BODIPY FL C5</td>
			<td style="width:143px;">Thermo Fisher Scientific</td>
			<td style="width:127px;">D2183</td>
			<td>Fluorescent lipid analog; (4,4-Difluoro-5,7-Dimethyl-4-Bora-3a,4a-Diaza-s-Indacene-3-Propionic Acid)</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:231px;">TopFluor cholesterol&#160;</td>
			<td style="width:143px;">Avanti Polar Lipids Inc.</td>
			<td style="width:127px;">810255</td>
			<td>Fluorescent lipid analog; 23-(dipyrrometheneboron difluoride)-24-norcholesterol</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:231px;">Fatty acid-free BSA</td>
			<td>Sigma-Aldrich</td>
			<td style="width:127px;">A0281-1G</td>
			<td>For TopFluor cholesterol solubilization</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:231px;">Methyl cellulose</td>
			<td>Sigma-Aldrich</td>
			<td style="width:127px;">M0387</td>
			<td>Mounting media for live larval imaging; 75 x 25 x 1 mm</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:231px;">Low melt agarose</td>
			<td style="width:143px;">Thermo Fisher Scientific</td>
			<td style="width:127px;">BP165-25</td>
			<td>Mounting media for live larval imaging; 22 x 30</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:231px;">VWR microscope slides&#160;</td>
			<td style="width:143px;">VWR&#160;</td>
			<td style="width:127px;">16004-422</td>
			<td>Mounting larvae for live imaging</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:231px;">Coverslips&#160;</td>
			<td style="width:143px;">Cover Glass</td>
			<td style="width:127px;">12-544A</td>
			<td>Mounting larvae for live imaging</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:231px;">Super glue</td>
			<td style="width:143px;">Loctite</td>
			<td style="width:127px;">LOC01-30379</td>
			<td>Mounting larvae for live imaging</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:231px;">FluoroDish (glass bottom dish)</td>
			<td style="width:143px;">World Precision Instruments, Inc.&#160;</td>
			<td style="width:127px;">FD35-100</td>
			<td>Mounting larvae for live imaging; 35 mm dish, 23 mm glass, 0.17 mm glass thickness&#160;&#160;</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:231px;">Confocal microscope</td>
			<td>Leica Microsytems</td>
			<td style="width:127px;">SP-2, SP-5</td>
			<td>Microscope for high magnification live imaging</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:231px;">Stereoscope</td>
			<td style="width:143px;">Nikon</td>
			<td style="width:127px;">SM21500</td>
			<td>Microscope for low magnification live imaging</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:231px;">Glass culture tubes&#160;</td>
			<td style="width:143px;">Kimble</td>
			<td style="width:127px;">73500-13100</td>
			<td>Lipid extraction; (13 x 100 mm; 13 ml)</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:231px;">Savant SpeedVac Plus&#160;</td>
			<td style="width:143px;">ThermoQuest</td>
			<td style="width:127px;">SC210A</td>
			<td>Lipid extraction</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:231px;">Channeled TLC plates</td>
			<td style="width:143px;">Whatman Scientific</td>
			<td style="width:127px;">WC4855-821</td>
			<td>Food intake assay; LK5D Silica Gel 150 A, 20 x 20 cm, 250 um thick; Discontinued</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:231px;">Channeled TLC plates</td>
			<td style="width:143px;">Analtech, Inc.</td>
			<td style="width:127px;">66911</td>
			<td>Food intake assay; Direct replacement for Whatman Scientific TLC plates</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Typhoon 9410 Variable Mode Imager</td>
			<td style="width:143px;">GE Healthcare</td>
			<td style="width:127px;">9410</td>
			<td>Fluorescent plate reader for food intake assay</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:231px;">ImageQuant software</td>
			<td style="width:143px;">GE Healthcare</td>
			<td>29000605</td>
			<td>Analysis of food intake assay</td>
		</tr>
		<tr height="40">
			<td height="40" style="height:40px;width:231px;">5 3/4&#8217; Wide bore, borosilicate disposable pasteur pipets&#160;&#160;&#160;</td>
			<td style="width:143px;">Kimble</td>
			<td style="width:127px;">63A53WT</td>
			<td>Transfering larvae</td>
		</tr>
	</tbody>
</table>

high-fat feeding paradigm for larval zebrafish: feeding, live imaging, and quantification of food intake

Zebrafish are emerging as a model of dietary lipid processing and metabolic disease. This protocol describes how to feed larval zebrafish a lipid-rich meal, which consists of an emulsion of chicken egg yolk liposomes created by sonicating egg yolk in embryo media. Detailed instructions are provided to screen larvae for egg yolk consumption so that larvae that fail to feed will not confound experimental results. The chicken egg yolk liposomes can be spiked with fluorescent lipid analogs, including fatty acids and cholesterol, enabling both systemic and subcellular visualization of dietary lipid processing. Several methods are described to mount larvae that are conducive to short- and long-term live imaging with both upright and inverted objectives at high and low magnification. Additionally presented is an assay to quantify larval food intake by extracting the lipids of larvae fed fluorescent lipid analogs, spotting the lipids on a thin layer chromatography plate, and quantifying the fluorescence. Finally, critical aspects of the procedures, important controls, options for modifying the protocols to address specific experimental questions, and potential limitations are discussed. These techniques can be applied not only to focused, hypothesis driven inquiries, but also to a variety of screens and live imaging techniques to study dietary lipid metabolism and the control of food intake.

When fed on a rocker at 29-31 &#176;C, the majority of healthy larvae (&#8805;95%) will eat within 1 hr. Upon consuming the egg yolk emulsion, the larval intestine darkens in color. Very dark intestines can be observed at 2 hr (Figure 1). If larvae are unfed or fail to feed, the intestine remains clear. Larvae fed egg white exhibit a distended intestinal lumen that does not darken in color.
<img alt="Figure 1" src="/files/ftp_upload/54735/54735...

Watch this Scientific Journal Video about High-fat Feeding Paradigm for Larval Zebrafish: Feeding, Live Imaging, and Quantification of Food Intake at JoVE.com

High-fat Feeding Paradigm for Larval Zebrafish: Feeding, Live Imaging, and Quantification of Food Intake

Zebrafish are emerging as a valuable model of dietary lipid processing and metabolic disease. Described are protocols of lipid-rich larval feeds, live imaging of dietary fluorescent lipid analogs, and quantification of food intake. These techniques can be applied to a variety of screening, imaging, and hypothesis driven inquiry techniques.

Zebrafish are emerging as a model of dietary lipid processing and metabolic disease. This protocol describes how to feed larval zebrafish a lipid-rich ...

The overall goal of this experimental protocol is to feed larval Zebrafish a lipid rich meal that can be spiked with a fluorescent lipid analog to mount the larvae to visual lipid uptake dynamics and to quantify dietary lipid intake. This method can help answer key questions in the fields of metabolism and gastrointestinal biology, such as how dietary lipids are metabolized and how food intake is regulated. The main advantage of this technique is that fluorescent lipid analogs can efficiently be delivered in dietary liposomes.The optical clarity of the larval Zebrafish enables microscopy to reveal subcellular lipid processing. To begin, suspend one milligram of powdered fluorescent lipid analog in two milliliters of 100%chloroform for a final concentration of 0.5 micrograms per microliter. Aliquot the analog into amber glass tubes with screw caps compatible with the solvent that contain a Teflon gasket.Store these stocks in the freezer. Add 10.4 microliters of the 0.5 microgram per microliter fluorescent lipid analog stock to a 1.5 milliliter tube and dry under a stream of nitrogen, taking care not to blow the lipid out of the tube. Immediately resuspend the dried lipid in five microliters of 100%ethanol by pipetting a stream down the sides of the tube.Then, add 95 microliters of embryo medium and mix thoroughly by pipetting up and down until the mixture appears homogeneous. Protect the tube from light and store it on ice until needed. To make a fluorescent cholesterol liposome solution, add enough fluorescent cholesterol analog stock into a 1.5 milliliter tube to make a final concentration of 2.5 micrograms per milliliter when it is added to the egg yolk emulsion.Dry the cholesterol stock under a stream of nitrogen, as before. Immediately resuspend the fluorescent cholesterol analog in 15 microliters of room temperature 100%ethanol by pipetting a stream down the side of the tube. And mix with 85 microliters of 1%fatty acid free BSA and water.It is essential to completely solubilize the fluorescent lipid analog in ethanol and embryo media prior to adding it to the egg yolk emulsion to ensure homogeneous distribution of the lipid in the feed and even availability to all larvae. Protect the tube from light with foil and store it on ice. To make the feeding solution, add 19 milliliters of embryo medium to a 50 milliliter conical tube, and then add a one milliliter egg yolk aliquot.Vortex the mixture for one to two minutes to make a homogeneous emulsion. Pour the mix through a fine strainer to remove protein conglomerates and collect it into a fresh 50 milliliter conical tube. Next, pulse sonicate the egg mix five times, one second on, one second off, with a 1/4 inch tapered microtip at six watts.Repeat the sonication program four additional times. This creates the liposomes, which should now be continuously rocked until use to maintain homogeneity. Add the appropriate amount of fluorescent lipid analogs to five milliliters of the liposome mixture immediately after sonication.Vortex at high speed for 30 seconds to incorporate the fluorescent lipid analogs into the liposomes. Protect the mixture from light by wrapping the tube in foil, and return it to the rocker. Add fifty larvae to a feeding dish, remove the embryo medium, and add 5 milliliters of feed.To encourage food intake, gently rock the larvae in an incubated rocker and shield from light if fluorescent lipid analogs are in use. At the end of the feeding period, wash the larvae in five milliliters of embryo medium three times. To immobilize the larvae, place a metal block on ice, overlay a tissue to prevent excessive cooling, and then place the larvae in the dish of embryo medium on top to cool.Observe the larvae at 10x under a dissecting microscope, and determine which of them have consumed the liposome feed. Larvae that have consumed liposomes will have a darkened intestine. It is critical to determine whether a larvae have fed by checking for a darkened intestine.Typically, one to five percent of the larvae will not eat, and could confound the experimental results if not identified and removed. For long-term, high magnification imaging with an inverted objective, first cool the larvae on a metal block on ice. Transfer a larva to a glass bottom dish, and remove the embryo medium by wicking with a tissue.Place a drop of 42 degree Celsius low melt 1.2%agarose on top of the larva, and immediately position with a poker. Remove the dish from the cold block and allow the agarose to sit for two to three minutes. Finally, add a sufficient volume of fresh embryo medium to cover the agarose and prevent desiccation.Specimens are now ready for imaging. At the end of a liposome feed, pool a minimum of 10 washed larvae in a 1.5 milliliter tube. Remove the embryo medium and then snap freeze the larvae.Repeat in a separate tube with 10 unfed larvae as a control. Keeping the sample on ice, add 100 microliters of homogenization buffer to each tube, and then homogenize with a microtip sonicator. Transfer the tissue to a 13 milliliter culture tube.Add 375 microliters of one to two chloroform to methanol to each homogenization buffer slurry. Vortex for 30 to 60 seconds, and then incubate for 10 minutes at room temperature. Add a further 125 microliters of chloroform, and vortex for 30 seconds.Next, add 125 microliters of 200 millimolar TRIS pH 7.5, vortex for 30 seconds, and then centrifuge at 2000 times g for five minutes protected from light. Remove samples from the centrifuge carefully to avoid disturbing the separate phases. Using a clean glass pipette, collect the lower organic phase and transfer it into a clean 13 milliliter glass tube.Carefully avoid transferring any of the upper aqueous or middle larval debris phases and discard them. Dry the organic phase under vacuum at 0.12 atmospheric pressure, while protecting it from light, taking care to stop once the liquid has evaporated. Resuspend a single sample in 10 microliters of two to one chloroform to methanol and spot the entire sample volume onto a channeled, thin-layer chromatography plate.Repeat with the remaining samples, spotting in evenly spaced intervals. Finally, scan the plate with a fluorescent plate reader. Examination of larvae fed on a rocker under experimental conditions shows darkened intestines, typical of fish that have consumed the egg yolk emulsion.Unfed larvae usually have clear intestines, so those that have not consumed the diet formula during the feeding period are easily distinguished. A larva fed with a fluorescent lipid analog visualizes the transport and accumulation of this dietary lipid. Here, the fluorescent signal is seen throughout the digestive organs after eight hours of feeding.Various lipid analogs are incorporated in, and thus visualize, unique sets of cellular structures since they are differentially metabolized into complex lipids. Here, Fluorescent-C16 and C12 analogs label lipid droplets. Fluorescent-C5 labels hepatic and pancreatic ducts, lipid droplets, cellular membranes, and arterial networks.And Fluorescent-C2 analog labels hepatic and pancreatic ducts and cellular membranes. Larval food intake assays were used to study the feeding of wild-type versus transgenic larvae overexpressing Apolipoprotein A4B1, and showed that over four hour feedings the transgenic larvae ate less than the wild-type. Breedings were normalized used paired, unfed control larvae.Quantification of the fluorescence of wild-type and transgenic larvae, which overexpress Apo A4 following feeding, show significantly reduced ingestion by the transgenic larvae when compared to the wild-type. Once mastered, the egg yolk fluorescent lipid analog feed can be prepared in about 15 minutes. Food intake can be quantified from 10 to 12 pooled samples in approximately four hours.While attempting this procedure, it's important to remember to screen larvae for developmental defects that may impair food intake, such as a malformed jaw, an underdeveloped intestine, or decreased mobility. Methods like pharmaceutical treatments or genome engineering can be incorporated into this experimental protocol in order to answer additional questions, like how specific proteins and cell signaling pathways regulate food intake and lipid metabolism. After it's development, this technique paved the way for researchers in the fields of gastrointestinal physiology and cell biology to visualize dietary lipid transport and accumulation in larval Zebrafish.After watching this video, you should have a good understanding of how to prepare a lipid rich larval Zebrafish feed, screen larvae for food intake, mount larvae for short and long-term imaging, and quantify food intake. Don't forget that working with a sonicator can be hazardous. Ear protection should be worn while performing this procedure.

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Research

JoVE Journal

Biology

Two-photon axotomy and time-lapse confocal imaging in live zebrafish embryos

Zebrafish have long been utilized to study the cellular and molecular mechanisms of development by time-lapse imaging of the living transparent embryo. Here we describe a method to mount zebrafish embryos for long-term imaging and demonstrate how to automate the capture of time-lapse images using a confocal microscope. We also describe a method to create controlled, precise damage to individual branches of peripheral sensory axons in zebrafish using the focused power of a femtosecond laser mounted on a two-photon microscope. The parameters for successful two-photon axotomy must be optimized for each microscope. We will demonstrate two-photon axotomy on both a custom built two-photon microscope and a Zeiss 510 confocal/two-photon to provide two examples.

Zebrafish trigeminal sensory neurons can be visualized in a transgenic line expressing GFP driven by a sensory neuron specific promoter 1. We have adapted this zebrafish trigeminal model to directly observe sensory axon regeneration in living zebrafish embryos. Embryos are anesthetized with tricaine and positioned within a drop of agarose as it solidifies. Immobilized embryos are sealed within an imaging chamber filled with phenylthiourea (PTU) Ringers. We have found that embryos can be continuously imaged in these chambers for 12-48 hours. A single confocal image is then captured to determine the desired site of axotomy. The region of interest is located on the two-photon microscope by imaging the sensory axons under low, non-damaging power. After zooming in on the desired site of axotomy, the power is increased and a single scan of that defined region is sufficient to sever the axon. Multiple location time-lapse imaging is then set up on a confocal microscope to directly observe axonal recovery from injury.

Here we describe a method for mounting zebrafish embryos for long-term imaging, two-photon imaging and tissue-damage techniques, and time-lapse confocal imaging.

Zebrafish have long been utilized to study the cellular and molecular mechanisms of development by time-lapse imaging of the living transparent embryo.  ...

Live Imaging of the Zebrafish Embryonic Brain by Confocal Microscopy

In this video, we demonstrate the method our lab has developed to analyze the cell shape changes and rearrangements required to bend and fold the developing zebrafish brain (Gutzman et al, 2008). Such analysis affords a new understanding of the underlying cell biology required for development of the 3D structure of the vertebrate brain, and significantly increases our ability to study neural tube morphogenesis. The embryonic zebrafish brain is shaped beginning at 18 hours post fertilization (hpf) as the ventricles within the neuroepithelium inflate. By 24 hpf, the initial steps of neural tube morphogenesis are complete. Using the method described here, embryos at the one cell stage are injected with mRNA encoding membrane-targeted green fluorescent protein (memGFP). After injection and incubation, the embryo, now between 18 and 24 hpf, is mounted, inverted, in agarose and imaged by confocal microscopy. Notably, the zebrafish embryo is transparent making it an ideal system for fluorescent imaging. While our analyses have focused on the midbrain-hindbrain boundary and the hindbrain, this method could be extended for analysis of any region in the zebrafish to a depth of 
80-100 &mu;m.

In this video, we demonstrate a method by which to analyze the developing vertebrate brain in live zebrafish embryos at single cell resolution by confocal microscopy. This includes the method by which we inject the single-cell zebrafish embryo and subsequently mount and image the developing brain.

In this video, we demonstrate the method our lab has developed to analyze the cell shape changes and rearrangements required to bend and fold the ...

Detection of Live Escherichia coli O157:H7 Cells by PMA-qPCR

A unique open reading frame (ORF) Z3276 was identified as a specific genetic marker for E. coli O157:H7. A qPCR assay was developed for detection of E. coli O157:H7 by targeting ORF Z3276. With this assay, we can detect as low as a few copies of the genome of DNA of E. coli O157:H7. The sensitivity and specificity of the assay were confirmed by intensive validation tests with a large number of E. coli O157:H7 strains (n = 369) and non-O157 strains (n = 112). Furthermore, we have combined propidium monoazide (PMA) procedure with the newly developed qPCR protocol for selective detection of live cells from dead cells. Amplification of DNA from PMA-treated dead cells was almost completely inhibited in contrast to virtually unaffected amplification of DNA from PMA-treated live cells. Additionally, the protocol has been modified and adapted to a 96-well plate format for an easy and consistent handling of a large number of samples. This method is expected to have an impact on accurate microbiological and epidemiological monitoring of food safety and environmental source.

Detection of Live Escherichia coli O157:H7 Cells by PMA-qPCR

A qPCR assay was developed for detection of Escherichia coli O157:H7 targeting a unique genetic marker, Z3276. The qPCR was combined with propidium monoazide (PMA) treatment for live cell detection. This protocol has been modified and adapted to a 96-well plate format for easy and consistent handling of numerous samples

A unique open reading frame (ORF) Z3276 was identified as a specific genetic marker for E. coli O157:H7. A qPCR assay was developed for detection of E. ...

Measuring Glutathione-induced Feeding Response in Hydra

Hydra is among the most primitive organisms possessing a nervous system and chemosensation for detecting reduced glutathione (GSH) for capturing the prey. The movement of prey organisms causes mechanosensory discharge of the stinging cells called nematocysts from hydra, which are inserted into the prey. The feeding response in hydra, which includes curling of the tentacles to bring the prey towards the mouth, opening of the mouth and consequent engulfing of the prey, is triggered by GSH present in the fluid released from the injured prey. To be able to identify the molecular mechanism of the feeding response in hydra which is unknown to date, it is necessary to establish an assay to measure the feeding response. Here, we describe a simple method for the quantitation of the feeding response in which the distance between the apical end of the tentacle and mouth of hydra is measured and the ratio of such distance before and after the addition of GSH is determined. The ratio, called the relative tentacle spread, was found to give a measure of the feeding response. This assay was validated using a starvation model in which starved hydra show an enhanced feeding response in comparison with daily fed hydra.

Here we describe a simple assay for the quantification of the feeding response in hydra induced by the reduced form of glutathione. This assay relies on measuring the distance between the apical end of the tentacle and mouth of hydra.

Hydra is among the most primitive organisms possessing a nervous system and chemosensation for detecting reduced glutathione (GSH) for capturing the prey. ...

Real-time In Vivo Recording of Arabidopsis Calcium Signals During Insect Feeding Using a Fluorescent Biosensor

Calcium ions are predicted to be key signaling entities during biotic interactions, with calcium signaling forming an established part of the plant defense response to microbial elicitors and to wounding caused by chewing insects, eliciting systemic calcium signals in plants. However, the role of calcium in vivo during biotic stress is still unclear. This protocol describes the use of a genetically-encoded calcium sensor to detect calcium signals in plants during feeding by a hemipteran pest. Hemipterans such as aphids pierce a small number of cells with specialized, elongated sucking mouthparts, making them the ideal tool to study calcium dynamics when a plant is faced with a biotic stress, which is distinct from a wounding response. In addition, fluorescent biosensors are revolutionizing the measurement of signaling molecules in vivo in both animals and plants. Expressing a GFP-based calcium biosensor, GCaMP3, in the model plant Arabidopsis thaliana allows for the real-time imaging of plant calcium dynamics during insect feeding, with a high spatial and temporal resolution. A repeatable and robust assay has been developed using the fluorescence microscopy of detached GCaMP3 leaves, allowing for the continuous measurement of cytosolic calcium dynamics before, during, and after insect feeding. This reveals a highly-localized rapid calcium elevation around the aphid feeding site that occurs within a few minutes. The protocol can be adapted to other biotic stresses, such as additional insect species, while the use of Arabidopsis thaliana allows for the rapid generation of mutants to facilitate the molecular analysis of the phenomenon.

Real-time In Vivo Recording of Arabidopsis Calcium Signals During Insect Feeding Using a Fluorescent Biosensor

This protocol outlines a simple method for analyzing calcium signals in plants generated by feeding hemipteran insects, such as aphids. Arabidopsis thaliana transformed with the GFP calcium biosensor GCaMP3 allow for the real-time in vivo imaging of calcium dynamics with a high temporal and spatial resolution.

Calcium ions are predicted to be key signaling entities during biotic interactions, with calcium signaling forming an established part of the plant ...

A Bacterial Oral Feeding Assay with Antibiotic-Treated Mosquitoes

The mosquito midgut harbors a highly dynamic microbiome that affects the host metabolism, reproduction, fitness, and vector competence. Studies have been conducted to investigate the effect of gut microbes as a whole; however, different microbes could exert distinct effects toward the host. This article provides the methodology to study the effect of each specific mosquito gut microbe and the potential mechanism.
This protocol contains two parts. The first part introduces how to dissect the mosquito midgut, isolate cultivable bacteria colonies, and identify bacteria species. The second part provides the procedure to generate antibiotic-treated mosquitoes and reintroduce one specific bacteria species.

This article presents a protocol to investigate the effect of individual mosquito gut bacteria, including isolation and identification of mosquito midgut cultivable microbes, antibiotic depletion of mosquito gut bacteria, and reintroduce one specific bacteria species.

The mosquito midgut harbors a highly dynamic microbiome that affects the host metabolism, reproduction, fitness, and vector competence. Studies have been ...

Plasmodium falciparum Gametocyte Culture and Mosquito Infection Through Artificial Membrane Feeding

Malaria remains one of the most important public health problems, causing significant morbidity and mortality. Malaria is a mosquito borne disease transmitted through an infectious bite from the female Anopheles mosquito. Malaria control will eventually rely on a multitude of approaches, which includes ways to block transmission to, through and from mosquitoes. To study mosquito stages of malaria parasites in the laboratory, we have optimized a protocol to culture highly infectious Plasmodium falciparum gametocytes, a parasite stage required for transmission from the human host to the mosquito vector. P. falciparum gametocytes mature through five morphologically distinct steps, which takes approximately 1-2 weeks. Gametocyte culture described in this protocol is completed in 15 days and are infectious to mosquitoes from days 15-18. These protocols were developed to maintain a continuous cycle of infection competent gametocytes and to maintain uninterrupted supply of mosquito stages of the parasite. Here, we describe the methodology of gametocyte culture and how to infect mosquitoes with these parasites using glass membrane feeders.

Plasmodium falciparum Gametocyte Culture and Mosquito Infection Through Artificial Membrane Feeding

Detailed investigations on mosquito stages of malaria parasites are critical to design effective transmission blocking strategies. This protocol demonstrates how to effectively culture infectious gametocytes and then feed these gametocytes to mosquitoes to generate mosquito stages of P. falciparum.

Malaria remains one of the most important public health problems, causing significant morbidity and mortality. Malaria is a mosquito borne disease ...

Tick Artificial Membrane Feeding for Ixodes scapularis

Ticks and their associated diseases are an important topic of study due to their public health and veterinary burden. However, the feeding requirements of ticks during both study and rearing can limit experimental questions or the ability of labs to research ticks and their associated pathogens. An artificial membrane feeding system can reduce these problems and open up new avenues of research that may not have been possible with traditional animal feeding systems. This study describes an artificial membrane feeding system that has been refined for feeding and engorgement success for all Ixodes scapularis life stages. Moreover, the artificial membrane feeding system described in this study can be modified for use with other tick species through simple refinement of the desired membrane thickness. The benefits of an artificial membrane feeding system are counterbalanced by the labor intensiveness of the system, the additional environmental factors that may impact feeding success, and the need to refine the technique for each new species and life stage of ticks.

Tick Artificial Membrane Feeding for Ixodes scapularis

Presented here is a method to blood feed ticks in vitro via an artificial membrane system to allow for partial or full engorgement of a variety of tick life stages.

Ticks and their associated diseases are an important topic of study due to their public health and veterinary burden. However, the feeding requirements of ...

Manipulation of Rhythmic Food Intake in Mice Using a Custom-Made Feeding System

Rhythmic gene expression is a hallmark of the circadian rhythm and is essential for driving the rhythmicity of biological functions at the appropriate time of day. Studies over the last few decades have shown that rhythmic food intake (i.e., the time at which organisms eat food during the 24 h day), significantly contributes to the rhythmic regulation of gene expression in various organs and tissues throughout the body. The effects of rhythmic food intake on health and physiology have been widely studied ever since and have revealed that restricting food intake for 8 h during the active phase attenuates metabolic diseases arising from a variety of obesogenic diets. These studies often require the use of controlled methods for timing the delivery of food to animals. This manuscript describes the design and use of a low-cost and efficient system, built in-house for measuring daily food consumption as well as manipulating rhythmic food intake in mice. This system entails the use of affordable raw materials to build cages suited for food delivery, following a user-friendly handling procedure. This system can be used efficiently to feed mice on different feeding regimens such as ad libitum, time-restricted, or arrhythmic schedules, and can incorporate a high-fat diet to study its effect on behavior, physiology, and obesity. A description of how wild-type (WT) mice adapt to the different feeding regimens is provided.

Restricting the timing of food intake has emerged as a promising intervention to attenuate diet-induced metabolic diseases. This manuscript details the construction and use of an efficient system built in-house for measuring and manipulating rhythmic food intake in mice.

Rhythmic gene expression is a hallmark of the circadian rhythm and is essential for driving the rhythmicity of biological functions at the appropriate ...

Assessment of Phytochemical Effects on Helicoverpa armigera Through Feeding Assay

Developing a Feeding Assay System for Evaluating the Insecticidal Effect of Phytochemicals on Helicoverpa armigera

Helicoverpa armigera, a lepidopteran insect, is a polyphagous pest with a worldwide distribution. This herbivorous insect is a threat to plants and agricultural productivity. In response, plants produce several phytochemicals that negatively impact the insect's growth and survival. This protocol demonstrates an obligate feeding assay method to evaluate the effect of a phytochemical (quercetin) on insect growth, development, and survival. Under controlled conditions, the neonates were maintained until the second instar on a pre-defined artificial diet. These second-instar larvae were allowed to feed on a control and quercetin-containing artificial diet for 10 days. The insects' body weight, developmental stage, frass weight, and mortality were recorded on alternate days. The change in body weight, the difference in feeding pattern, and developmental phenotypes were evaluated throughout the assay time. The described obligatory feeding assay simulates a natural mode of ingestion and can be scaled up to a large number of insects. It permits one to analyze phytochemicals' effect on the growth dynamics, developmental transition, and overall fitness of H. armigera. Furthermore, this setup can also be utilized to evaluate alterations in nutritional parameters and digestive physiology processes. This article provides a detailed methodology for feeding assay systems, which may have applications in toxicological studies, insecticidal molecule screening, and understanding chemical effects in plant-insect interactions.

Author Spotlight: Development and Challenges of Feeding Assays for Insect Pest Management 

This protocol describes the obligate feeding assay to evaluate the potentially toxic effect of a phytochemical on the lepidopteran insect larvae. This is a highly scalable insect bioassay, easy to optimize the sublethal and lethal dose, deterrent activity, and physiological effect. This could be used for screening eco-friendly insecticides.

Helicoverpa armigera, a lepidopteran insect, is a polyphagous pest with a worldwide distribution. This herbivorous insect is a threat to plants and ...