Name: generation of parabiotic zebrafish embryos by surgical fusion of developing blastulae
Uploaded: 2016-06-11T15:00:00
Description: Watch this Scientific Journal Video about Generation of Parabiotic Zebrafish Embryos by Surgical Fusion of Developing Blastulae at JoVE.com

We thank Julie R. Perlin for helpful comments on the manuscript. D.I.S. is supported by grants from the American Society of Hematology, the Cooley's Anemia Foundation, and the NIH (K01DK085217 and R03DK100672). E.J.H. is a Howard Hughes Medical Institute Fellow of the Helen Hay Whitney Foundation. B.L. is a Howard Hughes Medical Institute Medical Research Fellow. B.W.B. is supported by an Irvington Fellowship from the Cancer Research Institute and a Young Investigator Award from the Conquer Cancer Foundation of ASCO. L.I.Z. is supported by grants from the NIH (R01CA103846, P01HL032262, and R01HL04880), Taub Foundation for MDS Research, Harvard Stem Cell Institute, and is an investigator of the Howard Hughes Medical Institute.

This protocol was approved by Boston Children&#39;s Hospital Animal Care and Use Committee. This protocol is modified from a previously published method 15.
1. Preparation of Reagents (Days or Weeks in Advance)
<ol>
	<li>Prepare 1.5% agarose-coated dishes. Add 1.5 g agarose to 100 ml Zebrafish E3 medium in an Erlenmeyer flask. Heat, dissolve the agarose, and then pour approximately 5 ml into 100 mm diameter x 20 mm deep petri dishes. 
	Note: These are used for dechor...

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Parabiotic fusion has been a powerful tool to investigate cellular functions of candidate genes in adult murine models and chick embryos10-14. More recently, a blastula fusion method has been described for generating conjoined zebrafish embryos15. In the present protocol, video-based tutorials are used to demonstrate and better describe the methodology for creating parabiotic zebrafish embryos of different genetic backgrounds in order to study temporal, cell-intrinsic, and cell-extrinsic roles of ca...

Creation of genetic mosaics (chimeras) between wild-type and genetically modified animals&#160;is a well-established and classical strategy for investigating cell-intrinsic versus cell-extrinsic functions of candidate genes1-6. Blastula transplantation in zebrafish has been widely utilized to generate chimeric embryos for studies of cell-autonomy7-9. Depending on the tissue of interest, however, it can be challenging to predictably target donor cells to the desired tissue (e.g., blood) 1-3, 7-9. Mouse geneticists have long utilized parabiotic surgical methods to generate conjoined organisms with a shared circulation 10-14. Because the parabiotic animals share a common bloodstream, interactions between cells that originated from one animal with cells of the other animal of a different genetic background can be studied 10-16. Recently, Karima Kissa&#39;s group elegantly demonstrated the ability to create conjoined zebrafish embryos and then use this system to study hematopoietic stem and progenitor cell (HSPC) migration15. In addition, zebrafish parabiosis was recently used to investigate the role of endothelial cadherin 5 in hematopoietic stem cell (HSC) emergence and migration,16 and to study the role of stromal cells in the HSPC niche during zebrafish development 17.&#160;
Unlike mice, zebrafish embryos are transparent and allow for direct visualization of cells during parabiotic development, making the system uniquely powerful. The utility of parabiosis in zebrafish, however, is limited by a steep learning curve, and parabiotic surgery on the delicate embryos can be technically challenging without detailed instruction and visual demonstration. The goal of this protocol is to provide a set of clear, step-by-step instructions to accompany video-based tutorials on how to generate parabiotic zebrafish embryos for studying temporal, cell-intrinsic, or cell-extrinsic functions of a candidate gene(s) by surgical fusion of developing blastulae. Key modifications and additional recommendations for increasing parabiont survival and new experimental applications are included.

<table border="0" cellpadding="0" cellspacing="0" width="686">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Methyl cellulose</td>
			<td style="width:87px;">Sigma</td>
			<td style="width:167px;">M0387</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Individual components for E3/HCR:</td>
			<td></td>
			<td style="width:167px;">For 1L: 14,61g NaCl, 0,63g KCl, 2,43g CaCl2-2H2O, 1,99g MgSO4</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">NaCl (Sodium chloride)</td>
			<td style="width:87px;">Sigma-Aldrich</td>
			<td style="width:167px;">S9888</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">KCl (Potassium chloride)</td>
			<td>Sigma-Aldrich</td>
			<td style="width:167px;">P9541</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">CaCl2 (Calcium chloride dihydrate)</td>
			<td>Sigma-Aldrich</td>
			<td style="width:167px;">223506</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">MgSO4 (Magnessium sulfate heptahydrate)</td>
			<td>Sigma-Aldrich</td>
			<td style="width:167px;">230391</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hepes (1M ) buffer solution</td>
			<td style="width:87px;">ThermoFisher</td>
			<td>15630-080</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Name</td>
			<td style="width:87px;">Company</td>
			<td style="width:167px;">Catalog Number</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Antibiotics:</td>
			<td style="width:87px;"></td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Pen/Strep</td>
			<td style="width:87px;">gibco by Life technologies</td>
			<td>15140-120</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ampicilin sodium salt</td>
			<td style="width:87px;">Sigma Life Science</td>
			<td style="width:167px;">A0166</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Kanamycin sulfate from Streptomyces kanamyceticus</td>
			<td style="width:87px;">Sigma Life Science</td>
			<td style="width:167px;">K1377</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Name of Reagent/ Equipment</td>
			<td style="width:87px;">Company</td>
			<td style="width:167px;">Catalog Number</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">50 mg/ml Pronase from Streptomyces griseus</td>
			<td style="width:87px;">Roche</td>
			<td style="width:167px;">11459643001</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">capillary glass used for needles (Capillary Glass &#38; Filaments)</td>
			<td style="width:87px;">Sutter Instrument</td>
			<td style="width:167px;">ITEM#: BF 100-50-10</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Teasing needles with wooden handles</td>
			<td style="width:87px;">Fisher Scientific</td>
			<td>S07894</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Glass Pasteur pipettes</td>
			<td style="width:87px;">Fisherbrand</td>
			<td style="width:167px;">13-678-20A</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">10 mL pipette pump (green) (Pipette Pump Pipettor)</td>
			<td style="width:87px;">Novatech International</td>
			<td style="width:167px;">F37898-0000</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">100 mm diameter/ 20 mm deep plastic petri dishes (PETRI DISH, 100/20 MM, PS, CLEAR, WITH VENTS, 
			HEAVY DESIGN, 15 PCS./BAG )</td>
			<td>Greiner Bio-one</td>
			<td>664102</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Dextran, Cascade Blue, 10,000 MW, Anionic, Lysine Fixable</td>
			<td>ThermoFisher</td>
			<td>D-1976</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">PTU. working stock is 0.003% (50X is 0.15%). for 500ml, 0.75 g N-Phenylthiourea</td>
			<td style="width:87px;">Sigma-Aldrich</td>
			<td style="width:167px;">P7629</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tricaine (powder) (Tricaine Methanesulfonato, Tricaine-S)</td>
			<td style="width:87px;">Western Chemical Inc</td>
			<td style="width:167px;">MS 222</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">LMP agarose (Ultrapure LMP agarose)</td>
			<td style="width:87px;">Invitrogen</td>
			<td style="width:167px;">16520100</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">plastic transfer pipette (just the wide ended one I think)</td>
			<td style="width:87px;">Fisherbrand</td>
			<td style="width:167px;">137115AM</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Glass-bottom 6-well plates used for imaging</td>
			<td style="width:87px;">MatTek</td>
			<td>P06G1.5-20-F</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">plastic western gel loading tip fixed on the end of a wood-handled dissecting needle (GELoader tips)</td>
			<td style="width:87px;">Eppendorf</td>
			<td style="width:167px;">22351656</td>
		</tr>
		<tr height="21">
			<td colspan="2" height="21" style="height:21px;">glass cover slips, slides and vacuum grease if mounting for an upright microscope:</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Vaccum grease ( Dow Corning&#174; high-vacuum silicone grease 
			colorless, weight 5.3 oz (tube) )</td>
			<td style="width:87px;">Dow Corning</td>
			<td>Z273554</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:433px;">Glass cover slips</td>
			<td style="width:87px;">Corning Life Sciences</td>
			<td style="width:167px;">2960-244</td>
		</tr>
	</tbody>
</table>

generation of parabiotic zebrafish embryos by surgical fusion of developing blastulae

Surgical parabiosis of two animals of different genetic backgrounds creates a unique scenario to study cell-intrinsic versus cell-extrinsic roles for candidate genes of interest, migratory behaviors of cells, and secreted signals in distinct genetic settings. Because parabiotic animals share a common circulation, any blood or blood-borne factor from one animal will be exchanged with its partner and vice versa. Thus, cells and molecular factors derived from one genetic background can be studied in the context of a second genetic background. Parabiosis of adult mice has been &#160;used extensively to research aging, cancer, diabetes, obesity, and brain development. More recently, parabiosis of zebrafish embryos has been used to study the developmental biology of hematopoiesis. In contrast to mice, the transparent nature of zebrafish embryos permits the direct visualization of cells in the parabiotic context, making it a uniquely powerful method for investigating fundamental cellular and molecular mechanisms. The utility of this technique, however, is limited by a steep learning curve for generating the parabiotic zebrafish embryos. This protocol provides a step-by-step method on how to surgically fuse the blastulae of two zebrafish embryos of different genetic backgrounds to investigate the role of candidate genes of interest. In addition, the parabiotic zebrafish embryos are tolerant to heat shock, making temporal control of gene expression possible. This method does not require a sophisticated set-up and has broad applications for studying cell migration, fate specification, and differentiation in vivo during embryonic development.

Consistent with previously published studies15, successful parabiotic fusion of zebrafish embryos depends on the staging and orientation of the two embryos&#160;and the concentration of methylcellulose. With just a few simple, inexpensive tools, surgically fused developing blastulae were generated that grew into parabiotic embryos with shared circulation. These tools included a modified Pasteur pipette, a 10 ml pipette pump, and wood handled teasing needles which were used eith...

Watch this Scientific Journal Video about Generation of Parabiotic Zebrafish Embryos by Surgical Fusion of Developing Blastulae at JoVE.com

Generation of Parabiotic Zebrafish Embryos by Surgical Fusion of Developing Blastulae

This protocol provides step-by-step instruction on how to generate parabiotic zebrafish embryos of different genetic backgrounds. When combined with the unparalleled imaging capabilities of the zebrafish embryo, this method provides a uniquely powerful means to investigate cell-autonomous versus non-cell-autonomous functions for candidate genes of interest.

Surgical parabiosis of two animals of different genetic backgrounds creates a unique scenario to study cell-intrinsic versus cell-extrinsic roles for ...

The overall goal of this method is to generate parabiotic zebrafish embryos, which can be used for studying cell intrinsic versus cell extrinsic functions for candidate genes of interest. This method can help answer key questions of cell autonomy. For example, in the hematopoetic system, vital defects in HSC migration are intrinsic to the HSCs or the niche microenvironment.The main advantage of this protocol is an improved ability to successfully generate parabiotic zebrafish embryos. Generally, individuals new to this method will struggle, because the developing embryos are extremely fragile, and easily damaged. Visual demonstration of this method is critical, as the surgical stitching steps can be difficult to learn because they require a high degree of accuracy and precision.Here we provide step-by-step instructions to generate parabiotic zebrafish embryos by surgical fusion of developing blastulas. This method demonstrates how to increase efficiency of parabiotic fusions and enhance survival of conjoined embryos. After preparing reagents and tools according to the text protocol, prepare two to three modified Pasteur pipettes by briefly heating the end of the pipette over a Bunsen burner.Then, using large forceps, while it is still hot, bend the end of the pipette approximately 45 degrees. To ensure that there are no sharp edges that might damage the embryos, keep the end of the pipette over a Bunsen burner for one to two seconds. Using plasma DNA, mRNA or morpholino, micro-inject embryos within one hour of collection, and allow them to develop to the 256 cell stage.As the embryos approach the 256 cell stage, transfer each genetic background into separate agarose coated dishes, scratch-free glass beakers or petri dishes. After dechorionating the embryos according to the text protocol, thaw previously prepared methylcellulose, and use a tabletop centrifuge at maximum speed to pellet undissolved crystals, which will damage the embryos or rupture the yolks. In the meantime, using a marker, mark 12 to 15 pre-determined spots on the bottom-side of a 100 milliliter agarose coated petri dish.Then, after centrifugation, using the clear upper fraction of the methylcellulose, transfer one to 1.5 centimeter drops into the marked spots in the petri dish. Next, prepare one 40 milliliter aliquot of high-calcium ringer, or HCR solution per agarose coated dish just prepared. To each aliquot, add antibiotics as listed here.When ready to perform blastula fusions, use the aliquots of HCR with antibiotics to carefully fill each dish containing the methylcellulose droplets, taking care to not disrupt the droplets. Attach a modified glass Pasteur pipette prepared earlier to a 10 milliliter pipette pump. Then, under a stereoscope, collect one dechorionated embryo from each background.Before dispensing the two embryos, use the Pasteur pipette to make a small depression in the middle of the methylcellulose drop. Then, deposit the two embryos into the depression. Now, using a teasing needle with a gel loading tip on the end, use gentle sweeping motions without directly touching the embryos to carefully reposition the embryos within the methylcellulose, such that their animal poles are directly touching one another.Properly orienting the developing embryos dictates how the embryos will fuse and develop. For head-to-head fusions, ensure that each fusion is aligned at their animal poles. Allow the embryos to sit for five minutes for the methylcellulose to settle in around them.During this time, load the next pair into another drop. To perform the surgery, using the glass needle tool, carefully wound each embryo at their point of contact. Then, with a gentle sewing motion, pull the cells from the first embryo into the second embryo and back again.At the end of the motion, hold the needle in place for two to three seconds before very slowly drawing it away. Precision with the glass needle is critical to ensure the embryos are properly stitched together. Care must be used not to damage the yolk sacs while maintaining enough connection for successful fusion.Allow the embryos to sit for 10 to 15 minutes at room temperature. In the meantime, stitch additional pairs of embryos. After the incubation, assess whether the embryos have remained attached, and repeat the wounding step if needed.Incubate the embryos in the same dish and medium at 28.5 degrees Celsius overnight. By the following morning, the embryos will have moved out of the mostly dissolved methylcellulose. Remove any embryos that have not successfully fused.Then, decant the medium and use 25 milliliters of E3 to replace it. To acquire images of the fused embryos, prepare 0.8%low melting point agarose. While still hot, aliquot 1 milliliter of the agarose into 1.5 milliliter microfuge tubes set in a 37 degree Celsius heating block.Anesthetize the parabiotic embryos by adding one milliliter of four milligrams per milliliter pH 7.0 tricaine to the 25 milliliters of E3 medium containing the embryos. Gently swirl the dish so that the embryos pool in the middle. Then, using a wide-tipped plastic transfer pipette, draw up the embryos in as little liquid as possible.Next, turn the pipette upright and gently bounce the embryos so that they settle to the very bottom of the pipette. Then, transfer the embryos to a 1 milliliter aliquot of low melting point agarose by lightly touching the pipette tip on the surface of the agarose. Dispose of any excess liquid from the pipette, and use the pipette to gently mix the embryos in the agarose.Then, with the pipette, transfer the agarose and embryos to the well of a glass bottom six-well plate. Under a stereomicroscope, use a gel loading tip affixed to the end of a teasing needle to position the embryos close to the cover glass and in the desired orientation for imaging. After the agarose has set, and medium with tricaine has been added to the wells, use an inverted widefield epifluorescence laser scanning confocal, or spinning disk confocal microscope to acquire images.For a whole embryo field of view, use a 4X objective. Use a 20X objective to image a specific tissue. Process the images according to the text protocol.As shown here, after orienting two blastulas with their animal poles facing one another, the embryos were carefully wounded at their point of contact. A greater degree of wounding increased the likelihood of the embryos maintaining a connection that resulted in a successful fusion without additional morphological defects or delayed development. As demonstrated in this figure, by orienting the two blastula with their animal poles directly aligned, reliable head-to-head or yolk sac-to-yolk sac fusions were generated with shared circulation.In most instances, the embryos had two hearts pumping a shared common circulation. To confirm that the embryos indeed shared their circulation, fused transgenic embryos that had GFP-positive erythrocytes were fused to embryos that had mCherry-positive vascular endothelial cells. As seen in this movie, by 48 hours post-fertilization, GFP-positive erythrocytes were observed circulating through the Flik 1 HRAS mCherry partner embryo.Finally, to investigate temporal control of gene expression, one of the two embryos was injected with an hsp70 EGFP DNA construct. After a brief 30-minute heat shock at 37 degrees Celsius, a clear GFP signal was established in one of the embryos, and in some cases, GFP-positive cells were seen circulating in the un-injected partner embryo. Once mastered, this technique can be done in five hours if it is performed properly.While attempting this procedure, it's important to remember to be careful when stitching the two blastulas together, and to revisit fusions if the surgery was not successful on the first attempt. Following this procedure, additional methods like live cell imaging can be used to answer additional questions, like whether wild-type HSCs can function normally in a mutant niche or conversely, whether mutant HSCs can function in a wild-type niche. This technique provides a powerful method for researchers in the field of hematology to study the regulation of blood development in zebrafish.Don't forget that tricaince can be hazardous and precautions such as wearing appropriate safety attire should always be taken while performing this procedure. After watching this video and following our recommended techniques, we hope that you will be able to generate better biotic zebrafish embryos with greater success.

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Research

JoVE Journal

Developmental Biology

Mechanical Vessel Injury in Zebrafish Embryos

Zebrafish (Danio rerio) embryos have proven to be a powerful model for studying a variety of developmental and disease processes. External development and optical transparency make these embryos especially amenable to microscopy, and numerous transgenic lines that label specific cell types with fluorescent proteins are available, making the zebrafish embryo an ideal system for visualizing the interaction of vascular, hematopoietic, and other cell types during injury and repair in vivo. Forward and reverse genetics in zebrafish are well developed, and pharmacological manipulation is possible. We describe a mechanical vascular injury model using micromanipulation techniques that exploits several of these features to study responses to vascular injury including hemostasis and blood vessel repair. Using a combination of video and timelapse microscopy, we demonstrate that this method of vascular injury results in measurable and reproducible responses during hemostasis and wound repair. This method provides a system for studying vascular injury and repair in detail in a whole animal model.

This article describes a method for creating a mechanical vessel injury in zebrafish embryos. This injury model provides a platform for studying hemostasis, injury-related inflammation, and wound healing in an organism ideally suited for real-time microscopy.

Zebrafish (Danio rerio) embryos have proven to be a powerful model for studying a variety of developmental and disease processes.  External development ...

Isolation and Characterization of Single Cells from Zebrafish Embryos

The zebrafish (Danio rerio) is a powerful model organism to study vertebrate development. Though many aspects of zebrafish embryonic development have been described at the morphological level, little is known about the molecular basis of cellular changes that occur as the organism develops. With recent advancements in microfluidics and multiplexing technologies, it is now possible to characterize gene expression in single cells. This allows for investigation of heterogeneity between individual cells of specific cell populations to identify and classify cell subtypes, characterize intermediate states that occur during cell differentiation, and explore differential cellular responses to stimuli. This study describes a protocol to isolate viable, single cells from zebrafish embryos for high throughput multiplexing assays. This method may be rapidly applied to any zebrafish embryonic cell type with fluorescent markers. An extension of this method may also be used in combination with high throughput sequencing technologies to fully characterize the transcriptome of single cells. As proof of principle, the relative abundance of cardiac differentiation markers was assessed in isolated, single cells derived from nkx2.5 positive cardiac progenitors. By evaluation of gene expression at the single cell level and at a single time point, the data support a model in which cardiac progenitors coexist with differentiating progeny. The method and work flow described here is broadly applicable to the zebrafish research community, requiring only a labeled transgenic fish line and access to microfluidics technologies.

This protocol describes a method for isolating single cells from zebrafish embryos, enriching for cells of interest, capturing zebrafish cells in microfluidic based single cell multiplex systems, and assessing gene expression from single cells.

The zebrafish (Danio rerio) is a powerful model organism to study vertebrate development. Though many aspects of zebrafish embryonic development have been ...

Affinity Labeling Detection of Endogenous Receptors from Zebrafish Embryos

By combining the powers of Affinity Labeling and Immunoprecipitation (AFLIP), a technique for the detection of low abundance receptors in zebrafish embryos has been implemented. This technique takes advantage of the selectivity and sensitivity conferred by affinity labeling of a given receptor by its ligand with the specificity of the immunoprecipitation. We have used AFLIP to detect the type III TGF-&#946; receptor (TGFBR3), also know as betaglycan, during early zebrafish development. AFLIP was instrumental in validating the efficacy of a TGFBR3 morphant zebrafish phenotype. In the first step, embryo protein extracts are prepared and used to generate 125I-TGF-&#946;2-TGFBR3 complexes that are purified by immunoprecipitation. Later, these complexes are covalently cross-linked and revealed using SDS-PAGE separation and autoradiography detection. This technique requires the availability of a labeled ligand for, and a specific antibody against, the receptor to be detected, and shall be easily adapted to identify any growth factor or cytokine receptor that meets these requirements.

A novel technique for the detection of low abundance endogenous receptors present in zebrafish embryos is described. We have named it AFLIP because it consists of affinity labeling of the receptor by its ligand linked to immunoprecipitation.

By combining the powers of Affinity Labeling and Immunoprecipitation (AFLIP), a technique for the detection of low abundance receptors in zebrafish ...

Ploidy Manipulation of Zebrafish Embryos with Heat Shock 2 Treatment

Manipulation of ploidy allows for useful transformations, such as diploids to tetraploids, or haploids to diploids. In the zebrafish Danio rerio, specifically the generation of homozygous gynogenetic diploids is useful in genetic analysis because it allows the direct production of homozygotes from a single heterozygous mother. This article describes a modified protocol for ploidy duplication based on a heat pulse during the first cell cycle, Heat Shock 2 (HS2). Through inhibition of centriole duplication, this method results in a precise cell division stall during the second cell cycle. The precise one-cycle division stall, coupled to unaffected DNA duplication, results in whole genome duplication. Protocols associated with this method include egg and sperm collection, UV treatment of sperm, in vitro fertilization and heat pulse to cause a one-cell cycle division delay and ploidy duplication. A modified version of this protocol could be applied to induce ploidy changes in other animal species.

A modified protocol for ploidy manipulation uses a heat shock to induce a one-cycle stall in cytokinesis in the early embryo. This protocol is demonstrated in the zebrafish but may be applicable to other species.

Manipulation of ploidy allows for useful transformations, such as diploids to tetraploids, or haploids to diploids. In the zebrafish Danio rerio, ...

Biosensing Motor Neuron Membrane Potential in Live Zebrafish Embryos

The protocols described here are designed to allow researchers to study cell communication without altering the integrity of the environment in which the cells are located. Specifically, they have been developed to analyze the electrical activity of excitable cells, such as spinal neurons. In such a scenario, it is crucial to preserve the integrity of the spinal cell, but it is also important to preserve the anatomy and physiological shape of the systems involved. Indeed, the comprehension of the manner in which the nervous system-and other complex systems-works must be based on a systemic approach. For this reason, the live zebrafish embryo was chosen as a model system, and the spinal neuron membrane voltage changes were evaluated without interfering with the physiological conditions of the embryos. 
Here, an approach combining the employment of zebrafish embryos with a FRET-based biosensor is described. Zebrafish embryos are characterized by a very simplified nervous system and are particularly suited for imaging applications thanks to their transparency, allowing for the employment of fluorescence-based voltage indicators at the plasma membrane during zebrafish development. The synergy between these two components makes it possible to analyze the electrical activity of the cells in intact living organisms, without perturbing the physiological state. Finally, this non-invasive approach can co-exist with other analyses (e.g., spontaneous movement recordings, as shown here).

Protocols described here allow for the study of the electrical properties of excitable cells in the most non-invasive physiological conditions by employing zebrafish embryos in an in vivo system together with a fluorescence resonance energy transfer (FRET)-based genetically encoded voltage indicator (GEVI) selectively expressed in the cell type of interest.

The protocols described here are designed to allow researchers to study cell communication without altering the integrity of the environment in which the ...

Induction of Hypoxia in Living Frog and Zebrafish Embryos

Here, we introduce a novel system for hypoxia induction, which we developed to study the effects of hypoxia in aquatic organisms such as frog and zebrafish embryos. Our system comprises a chamber featuring a simple setup that is nevertheless robust to induce and maintain a specific oxygen concentration and temperature in any experimental solution of choice. The presented system is very cost-effective but highly functional, it allows induction and sustainment of hypoxia for direct experiments in vivo and for various time periods up to 48 h.
To monitor and study the effects of hypoxia, we have employed two methods - measurement of levels of hypoxia-inducible factor 1alpha (HIF-1&#945;) in whole embryos or specific tissues and determination of retinal stem cell proliferation by 5-ethynyl-2&#8242;-deoxyuridine (EdU) incorporation into the DNA. HIF-1&#945; levels can serve as a general hypoxia marker in the whole embryo or tissue of choice, here embryonic retina. EdU incorporation into the proliferating cells of embryonic retina is a specific output of hypoxia induction. Thus, we have shown that hypoxic embryonic retinal progenitors decrease proliferation within 1 h of incubation under 5% oxygen of both frog and zebrafish embryos.
Once mastered, our setup can be employed for use with small aquatic model organisms, for direct in vivo experiments, any given time period and under normal, hypoxic or hyperoxic oxygen concentration or under any other given gas mixture.

We introduce a novel hypoxic chamber system for use with aquatic organisms such as frog and zebrafish embryos. Our system is simple, robust, cost-effective and allows the induction and sustainment of hypoxia in vivo and for up to 48 h. We present 2 reproducible methods to monitor the effectiveness of hypoxia.

Here, we introduce a novel system for hypoxia induction, which we developed to study the effects of hypoxia in aquatic organisms such as frog and ...

Development of an In Vitro Assay to Quantitate Hematopoietic Stem and Progenitor Cells (HSPCs) in Developing Zebrafish Embryos

Hematopoiesis is an essential cellular process in which hematopoietic stem and progenitor cells (HSPCs) differentiate into the multitude of different cell lineages that comprise mature blood. Isolation and identification of these HSPCs is difficult because they are defined ex post facto; they can only be defined after their differentiation into specific cell lineages. Over the past few decades, the zebrafish (Danio rerio) has become a model organism to study hematopoiesis. Zebrafish embryos develop ex utero, and by 48 h post-fertilization (hpf) have generated definitive HSPCs. Assays to assess HSPC differentiation and proliferation capabilities have been developed, utilizing transplantation and subsequent reconstitution of the hematopoietic system in addition to visualizing specialized transgenic lines with confocal microscopy. However, these assays are cost prohibitive, technically difficult, and time consuming for many laboratories. Development of an in vitro model to assess HSPCs would be cost effective, quicker, and present fewer difficulties compared to previously described methods, allowing laboratories to quickly assess mutagenesis and drug screens that affect HSPC biology. This novel in vitro assay to assess HSPCs is performed by plating dissociated whole zebrafish embryos and adding exogenous factors that promote only HSPC differentiation and proliferation. Embryos are dissociated into single cells and plated with HSPC-supportive colony stimulating factors that cause them to generate colony forming units (CFUs) that arise from a single progenitor cell. These assays should allow more careful examination of the molecular pathways responsible for HSPC proliferation, differentiation, and regulation, which will allow researchers to understand the underpinnings of vertebrate hematopoiesis and its dysregulation during disease.

Development of an In Vitro Assay to Quantitate Hematopoietic Stem and Progenitor Cells HSPCs in Developing Zebrafish Embryos

Here, we present a simple method to quantitate hematopoietic stem and progenitor cells (HSPCs) in embryonic zebrafish. HSPCs from dissociated zebrafish are plated in methylcellulose with supportive factors, differentiating into mature blood. This allows the detection of blood defects and allows drug screening to be easily conducted.

Hematopoiesis is an essential cellular process in which hematopoietic stem and progenitor cells (HSPCs) differentiate into the multitude of different cell ...

Visualization of Cellular Electrical Activity in Zebrafish Early Embryos and Tumors

Bioelectricity, endogenous electrical signaling mediated by ion channels and pumps located on the cell membrane, plays important roles in signaling processes of excitable neuronal and muscular cells and many other biological processes, such as embryonic developmental patterning. However, there is a need for in vivo electrical activity monitoring in vertebrate embryogenesis. The advances of genetically encoded fluorescent voltage indicators (GEVIs) have made it possible to provide a solution for this challenge. Here, we describe how to create a transgenic voltage indicator zebrafish using the established voltage indicator, ASAP1 (Accelerated Sensor of Action Potentials 1), as an example. The Tol2 kit and a ubiquitous zebrafish promoter, ubi, were chosen in this study. We also explain&#160;the processes of Gateway site-specific cloning, Tol2 transposon-based zebrafish transgenesis, and the imaging process for early-stage fish embryos and fish tumors using regular epifluorescent microscopes. Using this fish line, we found that there are cellular electric voltage changes during zebrafish embryogenesis, and fish larval movement. Furthermore, it was observed that in a few zebrafish malignant peripheral nerve sheath tumors, the tumor cells were generally polarized compared to the surrounding normal tissues.

Here, we show the process of creating a cellular electric voltage reporter zebrafish line to visualize embryonic development, movement, and fish tumor cells in vivo.

Bioelectricity, endogenous electrical signaling mediated by ion channels and pumps located on the cell membrane, plays important roles in signaling ...

Surgical Size Reduction of Zebrafish for the Study of Embryonic Pattern Scaling

In the developmental process, embryos exhibit a remarkable ability to match their body pattern to their body size; their body proportion is maintained even in embryos that are larger or smaller, within certain limits. Although this phenomenon of scaling has attracted attention for over a century, understanding the underlying mechanisms has been limited, owing in part to a lack of quantitative description of developmental dynamics in embryos of varied sizes. To overcome this limitation, we developed a new technique to surgically reduce the size of zebrafish embryos, which have great advantages for in vivo live imaging. We demonstrate that after balanced removal of cells and yolk at the blastula stage in separate steps, embryos can quickly recover under the right conditions and develop into smaller but otherwise normal embryos. Since this technique does not require special equipment, it is easily adaptable, and can be used to study a wide range of scaling problems, including robustness of morphogen mediated patterning.&#160;

Here, we describe a method for reducing the size of zebrafish embryos without disrupting normal developmental processes. This technique enables the study of pattern scaling and developmental robustness against size change.

In the developmental process, embryos exhibit a remarkable ability to match their body pattern to their body size; their body proportion is maintained ...

Whole Mount Immunohistochemistry in Zebrafish Embryos and Larvae

Immunohistochemistry is a widely used technique to explore protein expression and localization during both normal developmental and disease states. Although many immunohistochemistry protocols have been optimized for mammalian tissue and tissue sections, these protocols often require modification and optimization for non-mammalian model organisms. Zebrafish are increasingly used as a model system in basic, biomedical, and translational research to investigate the molecular, genetic, and cell biological mechanisms of developmental processes. Zebrafish offer many advantages as a model system but also require modified techniques for optimal protein detection. Here, we provide our protocol for whole-mount fluorescence immunohistochemistry in zebrafish embryos and larvae. This protocol additionally describes several different mounting strategies that can be employed and an overview of the advantages and disadvantages each strategy provides. We also describe modifications to this protocol to allow detection of chromogenic substrates in whole mount tissue and fluorescence detection in sectioned larval tissue. This protocol is broadly applicable to the study of many developmental stages and embryonic structures.

Here, we present a protocol for fluorescent antibody-mediated detection of proteins in whole preparations of zebrafish embryos and larvae.

Immunohistochemistry is a widely used technique to explore protein expression and localization during both normal developmental and disease states. ...