This work was funded by a BBSRC grant to MEP (BB/H010297/1), a BBSRC quota studentship to SAR, and an MRC studentship to SWF.

<ol>
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The authors have no competing financial interests.

An essential part of this protocol is generating biologically active ligands that are normally processed, secreted, and able to elicit a response in the receiving cell, despite having a fluorescent moiety attached. It is critical to establish that the fluorescently-tagged gene product is biologically active using an appropriate assay. For Shh-GFP, the ability to activate the expression of ptc1 was confirmed16. Wnt8a has a remarkably potent ability to induce a secondary axis when expressed in a single ...

During early embryonic development, cells are progressively committed to follow specific lineages of differentiation: this means a group of totipotent (or pluripotent) cells become gradually restricted to establishing populations of progenitor cells determined to give rise to one cell type. Cell-cell signalling is central to the regulation of lineage specification during embryonic development. Manipulation of these signals will be required to direct stem cells toward particular fates to support novel medical treatments.
A relatively small number of signalling pathways are reiterated during development, including pathways responding to the TGF superfamily (nodals and BMPs)1-2, FGFs3, Wnts4, and Hedgehogs5. These secreted proteins bind receptors present on the cell membrane to activate signal transduction thereby altering gene expression and/or cell behaviour. The tight regulation of cell signalling is essential for cell lineage specification and normal development. While the cross-talk among these pathways is important in determining cell fate, a single ligand can itself elicit distinct responses at different concentrations. Morphogen gradients were described over 100 years ago as a theory to explain how different cell types can derive from a field of cells6. Signalling molecules produced by one group of cells may diffuse over a certain range, decreasing in concentration with a greater distance from the source. Cells exposed to the signal will respond to the local concentration at their position in the field of cells, with cells at distinct positions responding differently to different levels of the signal. Evidence for the existence of morphogens comes from studies of the early Drosophila embryo7 and the wing disc8, as well as the vertebrate limb9 and neural tube10.
Methods are needed to investigate how morphogen gradients are established and to identify other molecules important in regulating these gradients. Elegant experiments using immunohistochemistry to visualise endogenous proteins in vivo in the context of different genetic backgrounds have been used to investigate morphogen gradients11-12. However, good antibodies and specific mutants are not always available, so we describe here a protocol using overexpression of fluorescent ligands in Xenopus, to provide an alternative, simple method to dissect how exogenous gene products can influence distribution of ligands across a field of cells. Xenopus laevis provides an excellent system to undertake these types of experiments as their embryos develop externally so they are accessible at the earliest stages. Their large size (1-1.5mm in diameter) simplifies microinjection and surgical manipulation and by blastula stages the cells are easy to image as they are still relatively big (about 20&#181;m across). Overexpression studies in Xenopus are simple to do: mRNA injected into the early embryo can be targeted to particular cells and is efficiently translated.
The fluorescently tagged Wnt8a/Wnt11b-HA-eGFP constructs were generated using pCS2 Wnt8a-HA13, pCS2 Wnt11b-HA14 and eGFP. The HA peptide is important to include, not only to provide an additional molecular tag, but also because it is thought to act as a spacer separating the Wnt and eGFP proteins allowing both gene products to function. The construct used for the visualisation of Shh was previously used to generate a transgenic mouse expressing a Shh-eGFP fusion protein15; this was kindly provided by Andy McMahon. Importantly, the GFP tag for all the constructs is cloned 3&#8217; to the signal sequence such that it is retained after processing. It is also essential to ensure that the final protein includes sequences required for modifications, such the addition of lipids as is the case for Shh and Wnt ligands.The cDNAs were subcloned into the pCS2+ expression vector which is optimised for the prodution of synthetic mRNA; it includes an SP6 promoter and polyadenylation signal (http://sitemaker.umich.edu/dlturner.vectors).
The work described here provides a simple protocol for comparing the secretion and diffusion of fluorescently tagged Wnt and Shh tagged ligands. By injecting defined amounts of synthetic mRNA, the protocol circumnavigates any problems associated with variable expression from different vectors using different promoters. These methods have recently been applied to investigate the effects of the heparan sulfate endosulfatase Sulf1 on Shh-eGFP and Wnt8a/Wnt11b-HA-eGFP secretion and diffusion in Xenopus16-17.

<table>
	<tbody>
		<tr>
			<td>Agarose</td>
			<td>Melford</td>
			<td>MB 1200</td>
			<td></td>
		</tr>
		<tr>
			<td>Ammonium acetate</td>
			<td>Ambion</td>
			<td>From Megascript SP6 Kit AM 1330</td>
			<td></td>
		</tr>
		<tr>
			<td>Bicarbonate</td>
			<td>VWR International</td>
			<td>RC-091</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium nitrate</td>
			<td>Sigma</td>
			<td>C13961</td>
			<td></td>
		</tr>
		<tr>
			<td>Cap analog (m7G(5&#39;))</td>
			<td>Applied Biosystems</td>
			<td>AM 8050</td>
			<td></td>
		</tr>
		<tr>
			<td>Chloroform</td>
			<td>Sigma</td>
			<td>C 2432</td>
			<td></td>
		</tr>
		<tr>
			<td>&#160;L-Cysteine hydrochloride monohydrate</td>
			<td>Sigma</td>
			<td>C7880</td>
			<td></td>
		</tr>
		<tr>
			<td>dNTPs</td>
			<td>Invitrogen</td>
			<td>18427-013</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethylenediaminetetraacetic acid (EDTA)</td>
			<td>Sigma</td>
			<td>O3690</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>VWR International</td>
			<td>20821.33</td>
			<td></td>
		</tr>
		<tr>
			<td>Ficoll 400</td>
			<td>Sigma</td>
			<td>F 4375</td>
			<td></td>
		</tr>
		<tr>
			<td>Fiji image J software</td>
			<td>N/A</td>
			<td>N/A</td>
			<td>Free download http://fiji.sc/Fiji</td>
		</tr>
		<tr>
			<td>Gentamycin</td>
			<td>Melford</td>
			<td>G 0124</td>
			<td></td>
		</tr>
		<tr>
			<td>Glacial acetic acid</td>
			<td>Fisher Scientific</td>
			<td>A/0400/PB17</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass cover slips, No.1.5&#160;</td>
			<td>Scientific Laboratory Supplies</td>
			<td>22X22-SGJ3015. 22X50-SGJ3030&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass needle puller</td>
			<td>Narishige</td>
			<td>Narishige PC -10</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass pull needles</td>
			<td>Drummond Scientific</td>
			<td>3-000-203-G/X</td>
			<td></td>
		</tr>
		<tr>
			<td>Human chronic gonadotropin (HCG)</td>
			<td>Intervet</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Isopropanol</td>
			<td>Fisher Scientific</td>
			<td>P/7500/PB17</td>
			<td></td>
		</tr>
		<tr>
			<td>Lithium chloride (LiCl)</td>
			<td>Sigma</td>
			<td>L-7026</td>
			<td></td>
		</tr>
		<tr>
			<td>LSM710 and Zen software (2008-2010)</td>
			<td>Carl Zeiss</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Matlab software</td>
			<td>Mathworks</td>
			<td></td>
			<td>http://uk.mathworks.com/</td>
		</tr>
		<tr>
			<td>Molecular grade water&#160;</td>
			<td>Fisher Scientific</td>
			<td>BP 2819-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Nail varnish&#160;</td>
			<td>Boots</td>
			<td>Bar code 3600530 373048</td>
			<td></td>
		</tr>
		<tr>
			<td>Spectrophotometer</td>
			<td>Lab.tech International</td>
			<td>ND-1000 / ND8000</td>
			<td></td>
		</tr>
		<tr>
			<td>Petri dish (55mm)</td>
			<td>VWR International</td>
			<td>391-0865</td>
			<td></td>
		</tr>
		<tr>
			<td>Phenol-chloroform</td>
			<td>Sigma</td>
			<td>P3803</td>
			<td></td>
		</tr>
		<tr>
			<td>Photoshop software</td>
			<td>Adobe</td>
			<td>N/A</td>
			<td>http://www.photoshop.com/products</td>
		</tr>
		<tr>
			<td>High fidelity DNA polymerase and buffers&#160;</td>
			<td>Biolabs</td>
			<td>M0530S&#160; Buffer - M0531S</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium chloride (KCl)</td>
			<td>Fisher Scientific</td>
			<td>P/4280/53</td>
			<td></td>
		</tr>
		<tr>
			<td>PVC insulation tape</td>
			<td>Onecall</td>
			<td>SH5006MPK</td>
			<td></td>
		</tr>
		<tr>
			<td>Gel extraction kit&#160;</td>
			<td>Qiagen</td>
			<td>S28704</td>
			<td></td>
		</tr>
		<tr>
			<td>Restriction enzymes buffers</td>
			<td>Roche</td>
			<td colspan="2">SuRE/CUT Buffer Set 11082 035 001</td>
		</tr>
		<tr>
			<td>RNAse-free DNAse</td>
			<td>Promega</td>
			<td>ME10A</td>
			<td></td>
		</tr>
		<tr>
			<td>Steel back single edge blades</td>
			<td>Personna</td>
			<td>66-0403-0000</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium chloride (NaCl)</td>
			<td>Fisher Scientific</td>
			<td>27810.364</td>
			<td></td>
		</tr>
		<tr>
			<td>SP6 transcription kit</td>
			<td>Ambion</td>
			<td>AM1330</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass slides</td>
			<td>Thermo Fisher</td>
			<td>SHE 2505</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris base</td>
			<td>Invitrogen</td>
			<td>15504-020</td>
			<td></td>
		</tr>
		<tr>
			<td>Tungsten needles</td>
			<td>N/A</td>
			<td>N/A</td>
			<td>homemade</td>
		</tr>
		<tr>
			<td>Zen lite software</td>
			<td>Carl Zeiss</td>
			<td>N/A</td>
			<td>Free download&#160; http://www.zeiss.co.uk/microscopy/en_gb/downloads/zen.html</td>
		</tr>
	</tbody>
</table>

using confocal analysis of xenopus laevis to investigate modulators of wnt and shh morphogen gradients

This protocol describes a method to visualise ligands distributed across a field of cells. The ease of expressing exogenous proteins, together with the large size of their cells in early embryos, make Xenopus laevis a useful model for visualising GFP-tagged ligands. Synthetic mRNAs are efficiently translated after injection into early stage Xenopus embryos, and injections can be targeted to a single cell. When combined with a lineage tracer such as membrane tethered RFP, the injected cell (and its descendants) that are producing the overexpressed protein can easily be followed. This protocol describes a method for the production of fluorescently tagged Wnt and Shh ligands from injected mRNA. The methods involve the micro dissection of ectodermal explants (animal caps) and the analysis of ligand diffusion in multiple samples. By using confocal imaging, information about ligand secretion and diffusion over a field of cells can be obtained. Statistical analyses of confocal images provide quantitative data on the shape of ligand gradients. These methods may be useful to researchers who want to test the effects of factors that may regulate the shape of morphogen gradients.

Confocal analysis of animal cap explants expressing fluorescently tagged proteins provides an effective system for visualising ligand distribution under different experimental conditions. In one example, the distribution of GFP tagged Shh is shown (Figure 1). At the 2-cell stage, Xenopus embryos are injected into both cells with either with a control mRNA or with mRNA coding for Sulf1, an enzyme that modifies cell surface heparan sulfate and influences the Shh morphogen gradient16. Th...

Watch this Scientific Journal Video about Using Confocal Analysis of Xenopus laevis to Investigate Modulators of Wnt and Shh Morphogen Gradients at JoVE.com

Using Confocal Analysis of Xenopus laevis to Investigate Modulators of Wnt and Shh Morphogen Gradients

The manuscript here provides a simple set of methods for analysing the secretion and diffusion of fluorescently tagged ligands in Xenopus. This provides a context for testing the ability of other proteins to modify ligand distribution and allowing experiments that may give insight into mechanisms regulating morphogen gradients.

Using Confocal Analysis of Xenopus laevis to Investigate Modulators of Wnt and Shh Morphogen Gradients

This protocol describes a method to visualise ligands distributed across a field of cells. The ease of expressing exogenous proteins, together with the ...

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Research

JoVE Journal

Developmental Biology

11.0K Views.  The Bateson Centre, University of Sheffield. The manuscript here provides a simple set of methods for analysing the secretion and diffusion of fluorescently tagged ligands in Xenopus. This provides a context for testing the ability of other proteins to modify ligand distribution and allowing experiments that may give insight into mechanisms regulating morphogen gradients.

Video: Using Confocal Analysis of Xenopus laevis to Investigate Modulators of Wnt and Shh Morphogen Gradients

Understanding Early Organogenesis Using a Simplified In Situ Hybridization Protocol in Xenopus

Organogenesis is the study of how organs are specified and then acquire their specific shape and functions during development. The Xenopuslaevis embryo is very useful for studying organogenesis because their large size makes them very suitable for identifying organs at the earliest steps in organogenesis. At this time, the primary method used for identifying a specific organ or primordium is whole mount in situ hybridization with labeled antisense RNA probes specific to a gene that is expressed in the organ of interest. In addition, it is relatively easy to manipulate genes or signaling pathways in Xenopus and in situ hybridization allows one to then assay for changes in the presence or morphology of a target organ. Whole mount in situ hybridization is a multi-day protocol with many steps involved. Here we provide a simplified protocol with reduced numbers of steps and reagents used that works well for routine assays. In situ hybridization robots have greatly facilitated the process and we detail how and when we utilize that technology in the process. Once an in situ hybridization is complete, capturing the best image of the result can be frustrating. We provide advice on how to optimize imaging of in situ hybridization results. Although the protocol describes assessing organogenesis in Xenopus laevis, the same basic protocol can almost certainly be adapted to Xenopus tropicalis and other model systems.

Understanding Early Organogenesis Using a Simplified In Situ Hybridization Protocol in Xenopus

The Xenopus laevis embryo continues to be exceptionally useful in the study of early development due to its large size and ease of manipulation. A simplified protocol for whole mount in situ hybridization protocol is provided that can be used in the identification of specific organs in this model system.

Organogenesis is the study of how organs are specified and then acquire their specific shape and functions during development.  The Xenopuslaevis embryo ...

Manipulation and In Vitro Maturation of Xenopus laevis Oocytes, Followed by Intracytoplasmic Sperm Injection, to Study Embryonic Development

Amphibian eggs have been widely used to study embryonic development. Early embryonic development is driven by maternally stored factors accumulated during oogenesis. In order to study roles of such maternal factors in early embryonic development, it is desirable to manipulate their functions from the very beginning of embryonic development. Conventional ways of gene interference are achieved by injection of antisense oligonucleotides (oligos) or mRNA into fertilized eggs, enabling under- or over-expression of specific proteins, respectively. However, these methods normally require more than several hours until protein expression is affected, and, hence, the interference of gene functions is not effective during early embryonic stages. Here, we introduce an experimental system in which expression levels of maternal proteins can be altered before fertilization. Xenopus laevis oocytes obtained from ovaries are defolliculated by incubating with enzymes. Antisense oligos or mRNAs are injected into defolliculated oocytes at the germinal vesicle (GV) stage. These oocytes are in vitro matured to eggs at the metaphase II (MII) stage, followed by intracytoplasmic sperm injection (ICSI). By this way, up to 10% of ICSI embryos can reach the swimming tadpole stage, thus allowing functional tests of specific gene knockdown or overexpression. This approach can be a useful way to study roles of maternally stored factors in early embryonic development.

Manipulation and In Vitro Maturation of Xenopus laevis Oocytes, Followed by Intracytoplasmic Sperm Injection, to Study Embryonic Development

We describe methods of manipulating Xenopus laevis immature oocytes, in vitro maturation of oocytes to eggs, and intracytoplasmic sperm injection. This protocol allows degradation of some maternal proteins and overexpression of genes of interest at fertilization, and hence is valuable to study roles of specific factors in early embryonic development.

Amphibian eggs have been widely used to study embryonic development. Early embryonic development is driven by maternally stored factors accumulated during ...

Functional Cloning Using a Xenopus Oocyte Expression System

Identification of genes responsible for embryonic induction poses a number of challenges; to name a few, secreted molecules of interest may be low in abundance, may not be secreted but tethered to the signaling cell(s), or may require the presence of binding partners or upstream regulatory molecules. Thus in a search for gene products capable of eliciting an early lens-inductive response in competent ectoderm, we utilized an expression cloning system that would allow identification of paracrine or juxtacrine factors as well as transcriptional or other regulatory proteins. Pools of mRNA were injected into Xenopus oocytes, and responding tissue placed directly on the oocytes and co-cultured. Following functional cloning of ldb1 from a neural plate stage cDNA library based on its ability to elicit the expression of the early lens placode marker foxe3 in lens-competent animal cap ectoderm, we characterized the mRNA expression pattern, and assayed developmental progression following overexpression or knockdown of ldb1. This system is suitable in a very wide variety of contexts where identification of an inducer or its upstream regulatory molecules is sought using a functional response in competent tissue.

Functional Cloning Using a Xenopus Oocyte Expression System

We describe a Xenopus oocyte and animal cap system for the expression cloning of genes capable of inducing a response in competent ectoderm, and discuss techniques for the subsequent analysis of such genes. This system is useful in the functional identification of a wide range of gene products.

Identification of genes responsible for embryonic induction poses a number of challenges; to name a few, secreted molecules of interest may be low in ...

Loss- and Gain-of-function Approach to Investigate Early Cell Fate Determinants in Preimplantation Mouse Embryos

Gene silencing and overexpression techniques are instrumental for the identification of genes involved in embryonic development. Direct target gene modification in preimplantation embryos provides a means to study the underlying mechanisms of genes implicated in, for instance, cellular differentiation into the trophectoderm (TE) and the inner cell mass (ICM). Here, we describe a protocol that examines the role of neogenin as an authentic receptor for initial cell fate determination in preimplantation mouse embryos. First, we discuss the experimental manipulations that were used to produce gain and loss of neogenin function by microinjecting neogenin cDNA and shRNA; the effectiveness of this approach was confirmed by a strong correlation between the pair-wise expression levels of either red fluorescent protein (RFP) or green fluorescent protein (GFP) and the immunocytochemical quantification of neogenin expression. Secondly, overexpression of neogenin in preimplantation mouse embryos leads to normal ICM development while neogenin knockdown causes the ICM to develop abnormally, implying that neogenin could be a receptor that relays extracellular cues to drive blastomeres to early cell fates. Given the success of this detailed protocol in investigating the function of a novel embryonic developmental stage-specific receptor, we propose that it has the potential to aid in exploration and identification of other stage-specific genes during embryogenesis.

The goal of this protocol is to describe a loss- and gain-of function method that is applicable to identify neogenin as a stage-specific receptor that leads to trophectoderm and inner cell mass differentiation in preimplantation mouse embryos.

 Gene silencing and overexpression techniques are instrumental for the identification of genes involved in embryonic development. Direct target gene ...

Technique to Target Microinjection to the Developing Xenopus Kidney

The embryonic kidney of Xenopus&#160;laevis (frog), the pronephros, consists of a single nephron, and can be used as a model for kidney disease. Xenopus embryos are large, develop externally, and can be easily manipulated by microinjection or surgical procedures. In addition, fate maps have been established for early Xenopus embryos. Targeted microinjection into the individual blastomere that will eventually give rise to an organ or tissue of interest can be used to selectively overexpress or knock down gene expression within this restricted region, decreasing secondary effects in the rest of the developing embryo. In this protocol, we describe how to utilize established Xenopus fate maps to target the developing Xenopus kidney (the pronephros), through microinjection into specific blastomere of 4- and 8-cell embryos. Injection of lineage tracers allows verification of the specific targeting of the injection. After embryos have developed to stage 38 - 40, whole-mount immunostaining is used to visualize pronephric development, and the contribution by targeted cells to the pronephros can be assessed. The same technique can be adapted to target other tissue types in addition to the pronephros.

Technique to Target Microinjection to the Developing Xenopus Kidney

Here, we present a protocol to use fate maps and lineage tracers to target injections into individual blastomeres that give rise to the kidney of Xenopus laevis embryos.

The embryonic kidney of Xenopus&#160;laevis (frog), the pronephros, consists of a single nephron, and can be used as a model for kidney disease. Xenopus ...

Studying Wnt Signaling During Patterning of Conducting Airways

Wnt signaling pathways play critical roles during development of the respiratory tract. Defining precise mechanisms of differentiation and morphogenesis controlled by Wnt signaling is required to understand how tissues are patterned during normal development. This knowledge is also critical to determine the etiology of birth defects such as lung hypoplasia and tracheobronchomalacia. Analysis of earliest stages of development of respiratory tract imposes challenges, as the limited amount of tissue prevents the performance of standard protocols better suited for postnatal studies. In this paper, we discuss methodologies to study cell differentiation and proliferation in the respiratory tract. We describe techniques such as whole mount staining, processing of the tissue for confocal microscopy and immunofluorescence in paraffin sections applied to developing tracheal lung. We also discuss methodologies for the study of tracheal mesenchyme differentiation, in particular cartilage formation. Approaches and techniques discussed in the current paper circumvent the limitation of material while working with embryonic tissue, allowing for a better understanding of the patterning process of developing conducting airways.

The use of reporter mice coupled to whole mount and section staining, microscopy and in vivo assays facilitates the analysis of mechanisms underlying the normal patterning of the respiratory tract. Here we describe how these techniques contributed to the analysis of Wnt signaling during tracheal development.

Wnt signaling pathways play critical roles during development of the respiratory tract. Defining precise mechanisms of differentiation and morphogenesis ...

Building Finite Element Models to Investigate Zebrafish Jaw Biomechanics

Skeletal morphogenesis occurs through tightly regulated cell behaviors during development; many cell types alter their behavior in response to mechanical strain. Skeletal joints are subjected to dynamic mechanical loading. Finite element analysis (FEA) is a computational method, frequently used in engineering that can predict how a material or structure will respond to mechanical input. By dividing a whole system (in this case the zebrafish jaw skeleton) into a mesh of smaller 'finite elements', FEA can be used to calculate the mechanical response of the structure to external loads. The results can be visualized in many ways including as a 'heat map' showing the position of maximum and minimum principal strains (a positive principal strain indicates tension while a negative indicates compression. The maximum and minimum refer the largest and smallest strain). These can be used to identify which regions of the jaw and therefore which cells are likely to be under particularly high tensional or compressional loads during jaw movement and can therefore be used to identify relationships between mechanical strain and cell behavior. This protocol describes the steps to generate Finite Element models from confocal image data on the musculoskeletal system, using the zebrafish lower jaw as a practical example. The protocol leads the reader through a series of steps: 1) staining of the musculoskeletal components, 2) imaging the musculoskeletal components, 3) building a 3 dimensional (3D) surface, 4) generating a mesh of Finite Elements, 5) solving the FEA and finally 6) validating the results by comparison to real displacements seen in movements of the fish jaw.

Finite Element Analysis is a frequently used tool to investigate the mechanical performance of structures under load. Here we apply its use to modeling the biomechanics of the zebrafish jaw.

Skeletal morphogenesis occurs through tightly regulated cell behaviors during development; many cell types alter their behavior in response to mechanical ...

Visualization and Quantitative Analysis of Embryonic Angiogenesis in Xenopus tropicalis

Blood vessels supply oxygen and nutrients throughout the body, and the formation of the vascular network is under tight developmental control. The efficient in vivo visualization of blood vessels and the reliable quantification of their complexity are key to understanding the biology and disease of the vascular network. Here, we provide a detailed method to visualize blood vessels with a commercially available fluorescent dye, human plasma acetylated low density lipoprotein DiI complex (DiI-AcLDL), and to quantify their complexity in Xenopus tropicalis. Blood vessels can be labeled by a simple injection of DiI-AcLDL into the beating heart of an embryo, and blood vessels in the entire embryo can be imaged in live or fixed embryos. Combined with gene perturbation by the targeted microinjection of nucleic acids and/or the bath application of pharmacological reagents, the roles of a gene or of a signaling pathway on vascular development can be investigated within one week without resorting to sophisticated genetically engineered animals. Because of the well-defined venous system of Xenopus and its stereotypic angiogenesis, the sprouting of pre-existing vessels, vessel complexity can be quantified efficiently after perturbation experiments. This relatively simple protocol should serve as an easily accessible tool in diverse fields of cardiovascular research.

Visualization and Quantitative Analysis of Embryonic Angiogenesis in Xenopus tropicalis

This protocol demonstrates a fluorescence-based method to visualize the vasculature and to quantify its complexity in Xenopus tropicalis. Blood vessels can be imaged minutes after the injection of a fluorescent dye into the beating heart of an embryo after genetic and/or pharmacological manipulations to study cardiovascular development in vivo.

Blood vessels supply oxygen and nutrients throughout the body, and the formation of the vascular network is under tight developmental control. The ...

Microinjection of DNA into Eyebuds in Xenopus laevis Embryos and Imaging of GFP Expressing Optic Axonal Arbors in Intact, Living Xenopus Tadpoles

The primary visual projection of tadpoles of the aquatic frog Xenopus laevis serves as an excellent model system for studying mechanisms that regulate the development of neuronal connectivity. During establishment of the retino-tectal projection, optic axons extend from the eye and navigate through distinct regions of the brain to reach their target tissue, the optic tectum. Once optic axons enter the tectum, they elaborate terminal arbors that function to increase the number of synaptic connections they can make with target interneurons in the tectum. Here, we describe a method to express DNA encoding green fluorescent protein (GFP), and gain- and loss-of-function gene constructs, in optic neurons (retinal ganglion cells) in Xenopus embryos. We explain how to microinject a combined DNA/lipofection reagent into eyebuds of one day old embryos such that exogenous genes are expressed in single or small numbers of optic neurons. By tagging genes with GFP or co-injecting with a GFP plasmid, terminal axonal arbors of individual optic neurons with altered molecular signaling can be imaged directly in brains of intact, living Xenopus tadpoles several days later, and their morphology can be quantified. This protocol allows for determination of cell-autonomous molecular mechanisms that underlie the development of optic axon arborization in vivo.

Microinjection of DNA into Eyebuds in Xenopus laevis Embryos and Imaging of GFP Expressing Optic Axonal Arbors in Intact, Living Xenopus Tadpoles

This protocol aims to demonstrate how to microinject a DNA/DOTAP mixture into eyebuds of one day old Xenopus laevis embryos, and how to image and reconstruct individual green fluorescent protein (GFP) expressing optic axonal arbors in tectal midbrains of intact, living Xenopus tadpoles.

The primary visual projection of tadpoles of the aquatic frog Xenopus laevis serves as an excellent model system for studying mechanisms that regulate the ...

Fluorescent Calcium Imaging and Subsequent In Situ Hybridization for Neuronal Precursor Characterization in Xenopus laevis

Spontaneous intracellular calcium activity can be observed in a variety of cell types and is proposed to play critical roles in a variety of physiological processes. In particular, appropriate regulation of calcium activity patterns during embryogenesis is necessary for many aspects of vertebrate neural development, including proper neural tube closure, synaptogenesis, and neurotransmitter phenotype specification. While the observation that calcium activity patterns can differ in both frequency and amplitude suggests a compelling mechanism by which these fluxes might transmit encoded signals to downstream effectors and regulate gene expression, existing population-level approaches have lacked the precision necessary to further explore this possibility. Furthermore, these approaches limit studies of the role of cell-cell interactions by precluding the ability to assay the state of neuronal determination in the absence of cell-cell contact. Therefore, we have established an experimental workflow that pairs time-lapse calcium imaging of dissociated neuronal explants with a fluorescence in situ hybridization assay, allowing the unambiguous correlation of calcium activity pattern with molecular phenotype on a single-cell level. We were successfully able to use this approach to distinguish and characterize specific calcium activity patterns associated with differentiating neural cells and neural progenitor cells, respectively; beyond this, however, the experimental framework described in this article could be readily adapted to investigate correlations between any time-series activity profile and expression of a gene or genes of interest.

Fluorescent Calcium Imaging and Subsequent In Situ Hybridization for Neuronal Precursor Characterization in Xenopus laevis

We present a two-part protocol that combines fluorescent calcium imaging with in situ hybridization, allowing the experimenter to correlate patterns of calcium activity with gene expression profiles on a single-cell level.

Spontaneous intracellular calcium activity can be observed in a variety of cell types and is proposed to play critical roles in a variety of physiological ...