Name: grafting of beads into developing chicken embryo limbs to identify signal transduction pathways affecting gene expression
Uploaded: 2016-01-17T14:00:00
Description: Watch this Scientific Journal Video about Grafting of Beads into Developing Chicken Embryo Limbs to Identify Signal Transduction Pathways Affecting Gene Expression at JoVE.com

This work was partly funded by a University of Nottingham Early Career award to DS. RM is funded by the Higher Committee for Education Development of Iraq.

Ethics Statement: All these experiments follow the animal care and ethical guidelines of the University of Nottingham.
1. Preparation of Heparin Beads for Grafting
<ol>
	<li>Wash heparin beads thoroughly in PBS before use. Note: Beads can be stored at 4 &#176;C as a slurry in PBS.
	<ol>
		<li>Select beads for grafting by removing them from the stock with a 20 &#181;l pipette into a 1 ml drop of PBS. Then use a micropipette set to 2 &#181;l to transfer beads into a 20 &#181;l...

<ol>
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P., Lunn, J. S., Collins, B. J., Storey, K. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+discrete+period+of+FGF-induced+Erk1/2+signalling+is+required+for+vertebrate+neural+specification.">A discrete period of FGF-induced Erk1/2 signalling is required for vertebrate neural specification.</a> Development. 134, 2889-2894 (2007).</li><li>Martinez-Morales, P. L., 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=FGF+and+retinoic+acid+activity+gradients+control+the+timing+of+neural+crest+cell+emigration+in+the+trunk.">FGF and retinoic acid activity gradients control the timing of neural crest cell emigration in the trunk.</a> Journal of Cell Biology. 194, 489-503 (2011).</li><li>Olivera-Martinez, I., Storey, K. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wnt+signals+provide+a+timing+mechanism+for+the+FGF-retinoid+differentiation+switch+during+vertebrate+body+axis+extension.">Wnt signals provide a timing mechanism for the FGF-retinoid differentiation switch during vertebrate body axis extension.</a> Development. 134, 2125-2135 (2007).</li><li>Logan, M., Simon, H. G., Tabin, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differential+regulation+of+T-box+and+homeobox+transcription+factors+suggests+roles+in+controlling+chick+limb-type+identity.">Differential regulation of T-box and homeobox transcription factors suggests roles in controlling chick limb-type identity.</a> Development. 125, 2825-2835 (1998).</li><li>Borycki, A. G., Mendham, L., Emerson, C. 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The use of bead grafts applied directly to developing tissues in ovo is a powerful tool to dissect the role of growth factor signaling during development giving unparalleled control over the developmental stage at which they are applied and the duration of exposure.
The choice of bead for each type of molecule is important. Small hydrophobic molecules, such as the inhibitors described here and retinoic acid, usually bind well to derivatized AG 1-X2 beads although it is necessary to test the ef...

Avian embryos have provided a powerful tool for the study of development for many years1. One of their most useful characteristics is that they are relatively easy to manipulate. External development makes it possible to open the egg to access the embryo and perform various micromanipulations including examples such as the classic quail-chick chimera system for studying cell fate2,3, the injection of retroviruses for overexpression in specific tissues during development4,5 and explant culture to identify developmental signaling sources6. More recently chimeras generated between unlabeled hosts with grafts from a transgenic chicken line expressing GFP has shown that the combination of classical grafting and genetic modification can provide important insights into development7,8.
The ease with which the avian embryo can be manipulated has made it an excellent model for studying limb development9. Application of specific growth factors to developing limbs in vivo has been instrumental in identifying factors that alter limb patterning10,11 and continues to provide insights into this process12. This approach has also been used to study the factors that regulate muscle development and has uncovered roles for numerous signals such as Wnts13, BMPs14 and HGF15.
Recently this technique has been used to investigate the signals controlling myogenic gene expression in the limb bud and has shown that interactions between FGF18 and retinoic acid can control the timing of MyoD expression16. Using a combination of growth factors and small molecules that can be loaded onto beads and then grafted directly into specific tissues at defined developmental stages gives the opportunity to intervene at almost any time and region during development. This has been used to investigate many processes including somite patterning17,18, neural specification19, neural crest migration20 and axis extension21.
Here we describe a method for grafting beads soaked in either growth factors or inhibitors into developing chicken limbs. This has been used to determine the effects of these signals on myogenesis by analyzing muscle specific gene expression with in situ hybridization. We describe grafts using either heparin soaked beads, which are used for growth factors, or AG 1-X2 beads for small hydrophobic molecules such as retinoic acid or small molecule inhibitors of specific signaling pathways. However other beads are also available which have been used to deliver both FGFs22 and Shh23.

<table>
	<tbody>
		<tr>
			<td>Heparin acrylic beads</td>
			<td>Sigma</td>
			<td>H5263</td>
			<td>The acrylic-heparin beads used have been discontinued. However a replacement product is available, Heparin agarose beads, cat no H6508. These are transparent so harder to work with but can be stained with phenol red in the same way as AG 1-X2 beads,</td>
		</tr>
		<tr>
			<td>AG 1-X2 beads</td>
			<td>Bio-Rad</td>
			<td>140-1231</td>
			<td></td>
		</tr>
		<tr>
			<td>Affi Gel blue beads</td>
			<td>Bio-Rad</td>
			<td>153-7301; 153-7302</td>
			<td>These beads have been used with a range of growth factors including Shh and FGFs and can be used to replace heparin beads</td>
		</tr>
		<tr>
			<td>FGF18</td>
			<td>Peprotech</td>
			<td>100-28</td>
			<td>Resuspend in PBS with 0/1% BSA, prepare single use aliquots of 0.5-1ul and store at -80&#176;C. Batches and suppliers can vary so different concentrations should be tested to determine an effective dose.</td>
		</tr>
		<tr>
			<td>U0126</td>
			<td>Cell Signalling</td>
			<td>9903</td>
			<td>Make to 20mM stock in DMSO and store in single use aliquots at -80&#176;C. Protect from light.</td>
		</tr>
		<tr>
			<td>BMS-493</td>
			<td>Tocris Biosciences</td>
			<td>3509</td>
			<td>Resuspend in DMSO and store in single use aliquots at -80&#176;C. Protect from light.</td>
		</tr>
		<tr>
			<td>Black Indian ink</td>
			<td>Windsor and Newton</td>
			<td>5012572003384 (30ml)</td>
			<td>While alternatives to this product are available care should be taken as some inks are toxic to embryos</td>
		</tr>
		<tr>
			<td>Tungsten wire, 0.1mm dia. 99.95%</td>
			<td>Alfa Aesar</td>
			<td>10404</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin / streptomycin</td>
			<td>Sigma</td>
			<td>P0781</td>
			<td>Dilute 100X in PBS/ink and PBS/FCS</td>
		</tr>
	</tbody>
</table>

grafting of beads into developing chicken embryo limbs to identify signal transduction pathways affecting gene expression

Using chicken embryos it is possible to test directly the effects of either growth factors or specific inhibitors of signaling pathways on gene expression and activation of signal transduction pathways. This technique allows the delivery of signaling molecules at precisely defined developmental stages for specific times. After this embryos can be harvested and gene expression examined, for example by in situ hybridization, or activation of signal transduction pathways observed with immunostaining.
In this video heparin beads soaked in FGF18 or AG 1-X2 beads soaked in U0126, a MEK inhibitor, are grafted into the limb bud in ovo. This shows that FGF18 induces expression of MyoD and ERK phosphorylation and both endogenous and FGF18 induced MyoD expression is inhibited by U0126. Beads soaked in a retinoic acid antagonist can potentiate premature MyoD induction by FGF18.
This approach can be used with a wide range of different growth factors and inhibitors and is easily adapted to other tissues in the developing embryo.

At HH stage 21 MyoD is not expressed in developing limb myoblasts although staining can be seen in the myotome of the developing somites (Figure 1A). Figure 1B shows in situ hybridization for MyoD 6 hr following an FGF18 bead graft. MyoD is induced in myoblasts close to the bead while there is no expression in the contralateral limb. Co-grafting a bead soaked in U0126, a specific inhibitor of MEK, blocks FGF18 induction of MyoD (Figure 1C). Similarly grafting a ...

Watch this Scientific Journal Video about Grafting of Beads into Developing Chicken Embryo Limbs to Identify Signal Transduction Pathways Affecting Gene Expression at JoVE.com

Grafting of Beads into Developing Chicken Embryo Limbs to Identify Signal Transduction Pathways Affecting Gene Expression

By grafting beads soaked in growth factors or specific inhibitors of signaling pathways into developing embryos it is possible to directly test their effects in vivo. In this protocol beads are grafted into the limb bud to determine the effects of these molecules on gene expression and signal transduction.

Using chicken embryos it is possible to test directly the effects of either growth factors or specific inhibitors of signaling pathways on gene expression ...

The overall goal of this procedure is to show how to determine the effects of growth factors and inhibitors, in the gene expression of developing chicken embryo limbs. This method can help answer key questions in development biology, such as how signalling molecules influence the growth and differentiations of cells in vivo. The main advantage of this technique is that it provides a method to test these factors directly in the embryo.Though this method can provide insight into the limb development, it can also be applied to other systems, such as neural tissue, somites or gastrulation. Demonstrating the procedure will be Rebeea Mohammed, a graduate student from my laboratory. To begin, transfer one milliliter of the beads from the original stock solution into a fresh tube.Allow the beads to settle, then remove the liquid, and replace it with one milliliter of PBS. Repeat this step five times and store the washed beads at four degrees Celsius, as a slurry in PBS. Select the beads for grafting, by removing them from the washed stock solution using a 20 microliter pipette and place them into one milliliter of PBS.Using a stereoscope, choose beads that are around 100 microns in diameter. Transfer the selected beads in two micro-liters of liquid into a new Petri dish containing a 20 milliliter drop of PBS Next, remove the PBS from the beads. First, with 20 micro-liter pipette, and then, remove the residual liquid by capillary action using a fine watch-maker's forceps.It's important to remove as much liquid as possible so that the growth factor is not diluted when it's added to the beads. Pipette the growth factor directly onto the beads. For FGF18, add 0.5 micro-liters of recombinant FGF18, reconstituted add 0.5 milligrams per milliliter in PBS with 0.1 percent BSA.Then, place several drops of water around the edges of the dish to prevent the liquid from evaporating. When ready, incubate the beads for one hour at room temperature. Following incubation, remove the drops of water from the dish with a Pasteur pipette and place the dish on ice.Derivatize the beads, by first using a spatula to transfer the beads to a 1.5 milliliter micro-centrifuge tube. Then, add one milliliter of 0.2 normal formic acid and incubate the beads in the acid on a shaking platform for one hour. Next, allow the beads to settle, remove the formic acid and replace it with one milliliter of water.Wash the beads for one hour on the shaking platform and repeat the wash six times to remove any residual formic acid. Following the last wash, remove the remaining liquid and store the beads at four degrees Celsius. Use a spatula to remove a small palette of beads approximately five to ten micro-liters in volume from the stock, and place the beads into a 30 milliliter Petri dish.Then, add one milliliter of DMSO. Next, use a P2 pipette set to two micro-liters, to transfer beads of approximately 100 microns in diameter, to a 20 micro-liter drop of solvent in another 30 milliliter Petri dish. Remove the bulk of the solvent with a 20 micro-liter pipette and any residual solvent with a two micro-liter pipette.Then, cover the beads with 20 micro-liters of the drug to be applied, dissolved in DMSO. Incubate the beads in the drug solution for one hour. Protect the beads from light, as many drug molecules are light sensitive.To help visualize the beads, transfer four to five beads in two micro-liters of liquid, into 20 micro-liters of two percent phenol red dissolved in water. Remove a single bead with fine watch-maker's forceps and rinse the bead in PBS. Do not leave beads in the phenol red solution for more than 15 minutes before rinsing them, as this can cause lost of activity.Cut fine tungsten wire into three to four centimeter lengths Then, insert one piece of the wire, into the end of a glass Pasteur pipette and melt in a Bunsen burner to fix it in position. Prepare up to 10 needles to ensure that there are spares if they are damaged. Next, place the end of the wire into a blow-torch flame and hold it there until the tungsten glows white and tip is sharp.This takes around two to three minutes. Add five to six drops of artist India ink to 15 milliliters of PBS containing 100 units of Penicillin and 0.1 milligrams of Streptomycin per milliliter. To prepare the chicken embryos, incubate eggs with the blunt end up until they reach the desired stage for most limb bud manipulation, which is typically three to five days.When the desired time point is reached, use blunt forceps to tap on the blunt end of the egg and break the shell. Then, use the forceps to remove the shell and expose the embryo. Ensure the egg cell membrane is also removed.To visualize the embryo, inject PBS supplemented with a few drops of artist India ink, under the embryo with a one milliliter syringe and a 21 gauge needle. The vitelline membrane overlying the embryo, can then be removed with fine forceps. Next, add two to three milliliters of a supplemented PBS with one percent fetal calf serum, 100 units per milliliter of Penicillin, and 0.1 milligrams per milliliter of Streptomycin, into the egg to ensure that embryo does not dehydrate.Using sharpened watch-maker's forceps, open amnion over the developing limb buds. At these stages, the embryo will typically turn, so that the right side is upper most. Ensure the embryo does not dry out by adding more of the supplemented PBS solution when it is needed.The amnion surrounding the embryo can be opened using a fine tungsten needle to reveal the developing limb. Then, use the sharpened tungsten wire to make an incision into the limb bud where the bead will be implanted. Avoid cutting all the way through the limb bud, where possible.Although at younger stages, this is difficult. Pick up a bead, coated with either the growth factor or drug using extra fine, watch-maker's forceps. If the bead has been soaked in either DMSO or phenol red, be sure it gets rinsed with PBS before applying it to the embryo.Transfer the bead to the embryo using the forceps, and then, use the sharpened tungsten wire to insert the bead into the incision location. Add an additional one to two milliliters of the supplemented PBS solution to the egg to ensure that the embryo is kept hydrated. Avoid applying the solution directly onto the embryo itself, as this can damage the embryo and cause the bead to be dislodged.Next, use a ten milliliter syringe, equipped with a 19 gauge needle to remove only as much albumin as is needed to ensure that the embryo does not make contact with the tape used to seal the egg. Ensure that the needle does not damage the yolk, by sliding it down the inside of the shell. Finally, seal the egg with tape and return it to the incubator.In order to confirm that FGF18 is able to act through MEK to phosphorylate ERK, the embryos were harvested one hour after bead grafting and immunostained for the presence of phosphorylated ERK, which can be seen surround the grafted bead in the image on the right. At HH stage 21, MyoD is not expressed in developing limb myoblasts. Although staining can be seen in the myotome of the developing somites.Six hours following an FGF18 bead graft, MyoD can be seen induced in myoblast close to the bead. While there is no expression in the contralateral limb. This expression can be inhibited by co-grafting a bead, coated in a MEK inhibitor such as U0126.Similarly, grafting a U0126 bead at HH Stage 21 reduces the endogenous expression of MyoD after 24 hours, compared with the untreated contralateral limb. In limb buds, at HH stage 19, FGF18 does not induce MyoD. However, co-grafting of beads soaked in FGF18 and a retinoic acid antagonist can overcome this, and ectopic MyoD is detected.Once mastered, this technique can be done in three to four minutes, if it's performed properly. The development of this technique, allowed researchers in the field of development biology to explore growth factors signalling in embryo development. While attempting this technique, it's important to remember not to let the embryo dry out.After watching this video, you should have a good understanding of how to graft beads into developing embryos to determine how growth factors signalling affects development.

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Developmental Biology

Dual Labeling of Neural Crest Cells and Blood Vessels Within Chicken Embryos Using ChickGFP Neural Tube Grafting and Carbocyanine Dye DiI Injection

All developing organs need to be connected to both the nervous system (for sensory and motor control) as well as the vascular system (for gas exchange, fluid and nutrient supply). Consequently both the nervous and vascular systems develop alongside each other and share striking similarities in their branching architecture. Here we report embryonic manipulations that allow us to study the simultaneous development of neural crest-derived nervous tissue (in this case the enteric nervous system), and the vascular system. This is achieved by generating chicken chimeras via transplantation of discrete segments of the neural tube, and associated neural crest, combined with vascular DiI injection in the same embryo. Our method uses transgenic chickGFP embryos for intraspecies grafting, making the transplant technique more powerful than the classical quail-chick interspecies grafting protocol used with great effect since the 1970s. ChickGFP-chick intraspecies grafting facilitates imaging of transplanted cells and their projections in intact tissues, and eliminates any potential bias in cell development linked to species differences. This method takes full advantage of the ease of access of the avian embryo (compared with other vertebrate embryos) to study the co-development of the enteric nervous system and the vascular system.

Dual Labeling of Neural Crest Cells and Blood Vessels Within Chicken Embryos Using ChickGFP Neural Tube Grafting and Carbocyanine Dye DiI Injection

Here we report dual labeling of neural crest cells and blood vessels using chickGFP neural tube intraspecies grafting combined with intra-vascular DiI injection. This experimental technique allows us to simultaneously visualize and study development of the NCC-derived (enteric) nervous system and the vascular system, during organogenesis.

All developing organs need to be connected to both the nervous system (for sensory and motor control) as well as the vascular system (for gas exchange, ...

Gene Transfer into the Chicken Auditory Organ by In Ovo Micro-electroporation

Chicken embryos are ideal model systems for studying embryonic development as manipulations of gene function can be conducted with relative ease in ovo. The inner ear auditory sensory organ is critical for our ability to hear. It houses a highly specialized sensory epithelium that consists of mechano-transducing hair cells (HCs) and surrounding glial-like supporting cells (SCs). Despite structural differences in the auditory organs, molecular mechanisms regulating the development of the auditory organ are evolutionarily conserved between mammals and aves. In ovo electroporation is largely limited to early stages at E1 - E3. Due to the relative late development of the auditory organ at E5, manipulations of the auditory organ by in ovo electroporation past E3 are difficult due to the advanced development of the chicken embryo at later stages. The method presented here is a transient gene transfer method for targeting genes of interest at stage E4 - E4.5 in the developing chicken auditory sensory organ via in ovo micro-electroporation. This method is applicable for gain- and loss-of-functions with conventional plasmid DNA-based expression vectors and can be combined with in ovo cell proliferation assay by adding EdU (5-ethynyl-2&#180;-deoxyuridine) to the whole embryo at the time of electroporation. The use of green or red fluorescent protein (GFP or RFP) expression plasmids allows the experimenter to quickly determine whether the electroporation successfully targeted the auditory portion of the developing inner ear. In this method paper, representative examples of GFP electroporated specimens are illustrated; embryos were harvested 18 - 96 hr&#160;after electroporation and targeting of GFP to the pro-sensory area of the auditory organ was confirmed by RNA in situ hybridization. The method paper also provides an optimized protocol for the use of the thymidine analog EdU to analyze cell proliferation; an example of an EdU based cell proliferation assay that combines immuno-labeling and click EdU chemistry is provided.

Gene Transfer into the Chicken Auditory Organ by In Ovo Micro-electroporation

The auditory organ mediates hearing. Here we present a modified in ovo micro-electroporation method optimized for studying auditory progenitor cell proliferation and differentiation in the developing chicken auditory organ.

Chicken embryos are ideal model systems for studying embryonic development as manipulations of gene function can be conducted with relative ease in ovo. ...

In Vivo Imaging of Transgenic Gene Expression in Individual Retinal Progenitors in Chimeric Zebrafish Embryos to Study Cell Nonautonomous Influences

The genetic and technical strengths have made the zebrafish vertebrate a key model organism in which the consequences of gene manipulations can be traced in vivo throughout the rapid developmental period. Multiple processes can be studied including cell proliferation, gene expression, cell migration and morphogenesis. Importantly, the generation of chimeras through transplantations can be easily performed, allowing mosaic labeling and tracking of individual cells under the influence of the host environment. For example, by combining functional gene manipulations of the host embryo (e.g., through morpholino microinjection) and live imaging, the effects of extrinsic, cell nonautonomous signals (provided by the genetically modified environment) on individual transplanted donor cells can be assessed. Here we demonstrate how this approach is used to compare the onset of fluorescent transgene expression as a proxy for the timing of cell fate determination in different genetic host environments.
In this article, we provide the protocol for microinjecting zebrafish embryos to mark donor cells and to cause gene knockdown in host embryos, a description of the transplantation technique used to generate chimeric embryos, and the protocol for preparing and running in vivo time-lapse confocal imaging of multiple embryos. In particular, performing multiposition imaging is crucial when comparing timing of events such as the onset of gene expression. This requires data collection from multiple control and experimental embryos processed simultaneously. Such an approach can easily be extended for studies of extrinsic influences in any organ or tissue of choice accessible to live imaging, provided that transplantations can be targeted easily according to established embryonic fate maps.

In Vivo Imaging of Transgenic Gene Expression in Individual Retinal Progenitors in Chimeric Zebrafish Embryos to Study Cell Nonautonomous Influences

Live tracking of individual WT retinal progenitors in distinct genetic backgrounds allows for the assessment of the contribution of cell non-autonomous signaling during neurogenesis. Here, a combination of gene knockdown, chimera generation via embryo transplantation and in vivo time-lapse confocal imaging was utilized for this purpose.

The genetic and technical strengths have made the zebrafish vertebrate a key model organism in which the consequences of gene manipulations can be traced ...

Assessment of Ultrastructural Neuroplasticity Parameters After In Utero Transduction of the Developing Mouse Brain and Spinal Cord

The present study combines in utero transduction with transmission electron microscopy (TEM) aiming at a precise morphometrical analysis of ultrastructural parameters in unambiguously identified topographical structures, affected by a protein of interest that is introduced into the organism via viral transfer. This combined approach allows for a smooth transition from macrostructural to ultrastructural identification by following topographical navigation maps in a tissue atlas. High-resolution electron microscopy of the in-utero-transduced tissue reveals the fine ultrastructure of the neuropil and its plasticity parameters, such as cross-sectioned synaptic bouton areas, the number of synaptic vesicles and mitochondria within a bouton profile, the length of synaptic contacts, cross-sectioned axonal areas, the thickness of myelin sheaths, the number of myelin lamellae, and cross-sectioned areas of mitochondria profiles. The analysis of these parameters reveals essential insights into changes of ultrastructural plasticity in the areas of the nervous system that are affected by the viral transfer of the genetic construct. This combined method can not only be used for studying the direct effect of genetically engineered biomolecules and/or drugs on neuronal plasticity but also opens the possibility to study the in utero rescue of neuronal plasticity (e.g., in the context of neurodegenerative diseases).

The combination of transmission electron microscopy and in utero transduction is a powerful approach for studying morphological changes in the fine ultrastructure of the nervous system during development. This combined method allows deep insights into changes in structural details underlying neuroplasticity with respect to their topographical representation.

The present study combines in utero transduction with transmission electron microscopy (TEM) aiming at a precise morphometrical analysis of ...

Hemogenic Reprogramming of Human Fibroblasts by Enforced Expression of Transcription Factors

The cellular and molecular mechanisms underlying specification of human hematopoietic stem cells (HSCs) remain elusive. Strategies to recapitulate human HSC emergence in vitro are required to overcome limitations in studying this complex developmental process. Here, we describe a protocol to generate hematopoietic stem and progenitor-like cells from human dermal fibroblasts employing a direct cell reprogramming approach. These cells transit through a hemogenic intermediate cell-type, resembling the endothelial-to-hematopoietic transition (EHT) characteristic of HSC specification. Fibroblasts were reprogrammed to hemogenic cells via transduction with GATA2, GFI1B and FOS transcription factors. This combination of three factors induced morphological changes, expression of hemogenic and hematopoietic markers and dynamic EHT transcriptional programs. Reprogrammed cells generate hematopoietic progeny and repopulate immunodeficient mice for three months. This protocol can be adapted towards the mechanistic dissection of the human EHT process as exemplified here by defining GATA2 targets during the early phases of reprogramming. Thus, human hemogenic reprogramming provides a simple and tractable approach to identify novel markers and regulators of human HSC emergence. In the future, faithful induction of hemogenic fate in fibroblasts may lead to the generation of patient-specific HSCs for transplantation.

This protocol demonstrates the induction of a hemogenic program in human dermal fibroblasts by enforced expression of the transcription factors GATA2, GFI1B and FOS to generate hematopoietic stem and progenitor cells.

The cellular and molecular mechanisms underlying specification of human hematopoietic stem cells (HSCs) remain elusive. Strategies to recapitulate human ...

In Vitro Reconstitution of Spatial Cell Contact Patterns with Isolated Caenorhabditis elegans Embryo Blastomeres and Adhesive Polystyrene Beads

In multicellular systems, individual cells are surrounded by the various physical and chemical cues coming from neighboring cells and the environment. This tissue complexity confounds the identification of causal link between extrinsic cues and cellular dynamics. A synthetically reconstituted multicellular system overcomes this problem by enabling researchers to test for a specific cue while eliminating others. Here, we present a method to reconstitute cell contact patterns with isolated Caenorhabditis elegans blastomere and adhesive polystyrene beads. The procedures involve eggshell removal, blastomere isolation by disrupting cell-cell adhesion, preparation of adhesive polystyrene beads, and reconstitution of cell-cell or cell-bead contact. Finally, we present the application of this method to investigate the orientation of cellular division axes that contributes to the regulation of spatial cellular patterning and cell fate specification in developing embryos. This robust, reproducible, and versatile in vitro method enables the study of direct relationships between spatial cell contact patterns and cellular responses.

In Vitro Reconstitution of Spatial Cell Contact Patterns with Isolated Caenorhabditis elegans Embryo Blastomeres and Adhesive Polystyrene Beads

Tissue complexities of multicellular systems confound the identification of causal relationship between extracellular cues and individual cellular behaviors. Here, we present a method to study the direct link between contact-dependent cues and division axes using C. elegans embryo blastomeres and adhesive polystyrene beads.

In multicellular systems, individual cells are surrounded by the various physical and chemical cues coming from neighboring cells and the environment. ...

Laser Capture Microdissection of Mouse Embryonic Cartilage and Bone for Gene Expression Analysis

Laser capture microdissection (LCM) is a powerful tool to isolate specific cell types or regions of interest from heterogeneous tissues. The cellular and molecular complexity of skeletal elements increases with development. Tissue heterogeneity, such as at the interface of cartilaginous and osseous elements with each other or with surrounding tissues, is one obstacle to the study of developing cartilage and bone. Our protocol provides a rapid method of tissue processing and isolation of cartilage and bone that yields high quality RNA for gene expression analysis. Fresh frozen tissues of mouse embryos are sectioned and brief cresyl violet staining is used to visualize cartilage and bone with colors distinct from surrounding tissues. Slides are then rapidly dehydrated, and cartilage and bone are isolated subsequently by LCM. The minimization of exposure to aqueous solutions during this process maintains RNA integrity. Mouse Meckel&rsquo;s cartilage and mandibular bone at E16.5 were successfully collected and gene expression analysis showed differential expression of marker genes for osteoblasts, osteocytes, osteoclasts, and chondrocytes. High quality RNA was also isolated from a range of tissues and embryonic ages. This protocol details sample preparation for LCM including cryoembedding, sectioning, staining and dehydrating fresh frozen tissues, and precise isolation of cartilage and bone by LCM resulting in high quality RNA for transcriptomic analysis.

This protocol describes laser capture microdissection for the isolation of cartilage and bone from fresh frozen sections of the mouse embryo. Cartilage and bone can be rapidly visualized by cresyl violet staining and collected precisely to yield high quality RNA for transcriptomic analysis.

Laser capture microdissection (LCM) is a powerful tool to isolate specific cell types or regions of interest from heterogeneous tissues. The cellular and ...

Using Chicken Embryo as a Powerful Tool in Assessment of Developmental Cardiotoxicities

Chicken embryos are a classical model in developmental studies. During the development of chicken embryos, the time window of heart development is well-defined, and it is relatively easy to achieve precise and timely exposure via multiple methods. Moreover, the process of heart development in chicken embryos is similar to mammals, also resulting in a four-chambered heart, making it a valuable alternative model in the assessment of developmental cardiotoxicities. In our lab, the chicken embryo model is routinely used in the assessment of developmental cardiotoxicities following exposure to various environmental pollutants, including per- and polyfluoroalkyl substances (PFAS), particulate matter (PMs), diesel exhaust (DE) and nano materials. The exposure time can be freely selected based on the need, from the beginning of development (embryonic day 0, ED0) all the way to the day prior to hatch. The major exposure methods include air-cell injection, direct microinjection, and air-cell inhalation (originally developed in our lab), and the currently available endpoints include cardiac function (electrocardiography), morphology (histological assessments) and molecular biological assessments (immunohistochemistry, qRT-PCR, western blotting, etc.). Of course, the chicken embryo model has its own limitations, such as limited availability of antibodies. Nevertheless, with more laboratories starting to utilize this model, it can be used to make significant contributions to the study of developmental cardiotoxicities.

Chicken embryos, as a classical developmental model, are used in our lab to assess developmental cardiotoxicities following exposure to various environmental contaminants. Exposure methods and morphological/functional assessment methods established are described in this manuscript.

Chicken embryos are a classical model in developmental studies. During the development of chicken embryos, the time window of heart development is ...

Chicken Recombinant Limbs Assay to Understand Morphogenesis, Patterning, and Early Steps in Cell Differentiation

Cell differentiation is the fine-tuned process of cell commitment leading to the formation of different specialized cell types during the establishment of developing tissues and organs. This process is actively maintained in adulthood. Cell differentiation is an ongoing process during the development and homeostasis of organs. Understanding the early steps of cell differentiation is essential to know other complex processes such as morphogenesis. Thus, recombinant chicken limbs are an experimental model that allows the study of cell differentiation and pattern generation under embryonic patterning signals. This experimental model imitates an in vivo environment; it assembles reaggregated cells into an ectodermal cover obtained from an early limb bud. Later, ectoderms are transferred and implanted in a chick embryo receptor to allow its development. This assay was mainly used to evaluate mesodermal limb bud cells; however, it can be applied to other stem or progenitor cells from other organisms.

Recombinant limbs are a powerful experimental model that allows for studying the process of cell differentiation and the generation of patterns under the influence of embryonic signals. This protocol presents a detailed method for generating recombinant limbs with chicken limb-mesodermal cells, adaptable to other cell types obtained from different organisms.

Cell differentiation is the fine-tuned process of cell commitment leading to the formation of different specialized cell types during the establishment of ...

CRISPR/Cas9-Mediated Highly Efficient Gene Targeting in Embryonic Stem Cells for Developing Gene-Manipulated Mouse Models

The CRISPR/Cas9 system has made it possible to develop genetically modified mice by direct genome editing using fertilized zygotes. However, although the efficiency in developing gene-knockout mice by inducing small indel mutation would be sufficient enough, the efficiency of embryo genome editing for making large-size DNA knock-in (KI) is still low. Therefore, in contrast to the direct KI method in embryos, gene targeting using embryonic stem cells (ESCs) followed by embryo injection to develop chimera mice still has several advantages (e.g., high throughput targeting in vitro, multi-allele manipulation, and Cre and flox gene manipulation can be carried out in a short period). In addition, strains with difficult-to-handle embryos in vitro, such as BALB/c, can also be used for ESC targeting. This protocol describes the optimized method for large-size DNA (several kb) KI in ESCs by applying CRISPR/Cas9-mediated genome editing followed by chimera mice production to develop gene-manipulated mouse models.

Here we present a protocol for developing genetically modified mouse models using embryonic stem cells, especially for large DNA knock-in (KI). This protocol is tuned up using CRISPR/Cas9 genome editing, resulting in significantly improved KI efficiency compared with the conventional homologous recombination-mediated linearized DNA targeting method.

The CRISPR/Cas9 system has made it possible to develop genetically modified mice by direct genome editing using fertilized zygotes. However, although the ...