We are grateful to Gurdon laboratory members for useful discussion. K.M. is a Research Fellow at Wolfson College and is supported by the Herchel Smith Postdoctoral Fellowship and the Great Britain Sasakawa Foundation. Gurdon laboratory is supported by grants from the Wellcome Trust (RG69899) and MRC to J.B.G.

<ol>
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The authors have nothing to disclose.

We here detail a new method to deplete maternal factors or to overexpress exogenous factors before fertilization. This system requires two microinjections, but instead skips the surgery of frogs, used in the host transfer method7,17. It is optimal to remove the frog surgery step in terms of animal care. Moreover, we do not have to take into account for the quality of host female frogs for the transfer experiments, meaning that we can get rid of one biological factor that affects the success of experiments. Therefore in this system the quality of oocytes obtained from PMSG-primed frogs is a major biological factor that is key for successful experiments. The quality of oocytes can be judged after collection of ovary or after defolliculation. If any abnormality is observed at these stages, it is optimal to collect another ovary from a new frog. Another point when you can check the oocyte quality is after oocyte maturation. If less than 80% of progesterone-treated oocytes show signs of maturation, you may not be able to obtain the enough number of embryos for further analyses. The use of enzymatic defolliculation instead of manual defolliculation is also another advantage of using this system to reduce the labor required for defolliculation. However, it is still possible that manual defolliculation may give a better development than the enzymatic treatment.
As shown in Figure 3, almost 10% of in vitro matured oocytes can reach the swimming tadpole stage. These data are collected from 13 independent experiments including those reported in 8 and new injection experiments. Host transfer method needs 75-150 oocytes in each treatment for obtaining meaningful data since 30-60% of the transferred oocytes can reach the neurula stage17. Our method normally starts with 200-300 oocytes in each experimental group since approximately 40-60% of cleaved embryos can reach the muscular response stage. These data suggest that both methods support a reasonable developmental rate. We have so far obtained 10 alive frogs from control mRNA-injected and control antisense oligo-injected oocytes using this technique, indicating that this approach supports development through metamorphosis.
Our oocyte manipulation-ICSI method provides an opportunity to test the role of maternal factors during very early embryonic development, soon after fertilization. In addition, overexpression of chromatin modifying factors before fertilization may make it possible to remodel maternal chromatin before fertilization for understanding maternal chromatin states necessary for development. This strategy may also work well with current gene editing systems such as Transcription activator-like effector nuclease (TALEN)18,19 and CRISPR/CAS920,21 since these can be expressed even before fertilization. Therefore, our new approach has a potential to be used for many applications in future.

Xenopus laevis is a widely used, powerful model organism to study development1. This is because Xenopus eggs are unusually large (approximately 1.2-1.4 mm, in comparison to mammalian counterparts being about 0.1 mm) and abundant. Eggs contain maternally synthesized and stored components, which are enough to drive embryonic development until mid-blastula transition (MBT, occurring at the stage 8-8.5 with 4,000-8,000 cells). MBT is accompanied by zygotic genome activation, which then produces embryonic gene products that direct further development.
Numerous studies aimed to identify maternal factors important for development. Many studies rely on the injection of antisense oligonucleotides (oligos) including morpholino oligonucleotides into fertilized embryos, in which case degradation of maternal proteins can be observed at the gastrula stage2-4. Alternatively, mRNAs are injected to fertilized embryos to disturb gene functions or to trace fates of overexpressed proteins. However, the injection into the one-cell stage embryos normally does not affect expression levels of maternal proteins at the very early embryonic stages before MBT.
Heasman and Wylie established the host transfer method to overcome this issue5. In their method, manually defolliculated oocytes are injected with antisense oligos and transferred into host females6. Proteins are downregulated before fertilization so that roles of downregulated proteins in early embryonic development can be examined. This maternal depletion method led to the identification of several unique developmental roles of maternal proteins, as reviewed in 7.
In this report, we detail our recently developed method, in which maternal depletion or overexpression of mRNA before fertilization is achieved without manual defolliculation and host transfer8. Manual defolliculation requires a lot of time and host transfer often needs skillful techniques and the specific license for animal surgery, thus hampering the frequent use of maternal depletion method. Defolliculation and host transfer are substituted by enzymatic defolliculation 9,10 and intracytoplasmic sperm injection (ICSI)11-13, respectively. ICSI to eggs was originally used to produce transgenic frogs 12. Sperm and embryonic nuclei were also transplanted into in vitro matured amphibian oocytes 11,14,15. Here, we show our step-by-step method to inject sperm to in vitro matured oocytes that were pre-injected with antisense oligos or mRNA.

<table><tbody><tr><td>Pregnant Mare Serum Gonadotropin (PMSG)&amp;nbsp;</td><td>MSD Animal Health</td><td>Vm 01708/4309</td><td>PMSG-Intervet 5000iu powder and solvent for solution for injection</td></tr><tr><td>Ethyl 3-aminobenzoate methanesulfonate salt (MS222)</td><td>Sigma</td><td>A5040</td><td>For anesthesia</td></tr><tr><td>Liberase TM Research Grade</td><td>Roche</td><td>05 401 127 001</td><td>For oocyte defolliculation. Store at -20&amp;nbsp;&amp;#176;C.</td></tr><tr><td>Drummond Nanoject</td><td>Drummond Scientific Company</td><td>3-000-205/206</td><td>For microinjection</td></tr><tr><td>glass capillary&amp;nbsp;</td><td>Alpha laboratories</td><td>7&amp;rdquo; Drummond #3-000-203-G/XL</td><td>For microinjection</td></tr><tr><td>Micropipette Puller&amp;nbsp;</td><td>SUTTER Instrument</td><td>Model D-97</td><td>For microinjection</td></tr><tr><td>UltraPure Agarose</td><td>Invitrogen</td><td>16500-500</td><td>For &lt;em&gt;in vitro&lt;/em&gt; maturation and ICSI</td></tr><tr><td>14 ml ultra-clear centrifuge tube&amp;nbsp;</td><td>Beckman Coulter United Kingdom Ltd</td><td>344060</td><td>For sperm purification</td></tr><tr><td>OptiPrep Density Gradient Medium (Iodixanol)</td><td>Sigma</td><td>D1556</td><td>For sperm purification</td></tr><tr><td>Digitonin</td><td>Sigma</td><td>D141</td><td>Cell permeabilization reagent</td></tr><tr><td>Shaker</td><td>Hybaid&amp;nbsp;</td><td>HB-SHK-1</td><td>For oocyte defolliculation</td></tr><tr><td>Dissecting microscope (Stereo zoom microscope)</td><td>ZEISS</td><td>Semi SV6</td><td>For oocyte collection and microinjection</td></tr><tr><td>50 &amp;mu;m pore filter</td><td>CellTrics</td><td>04-0042-2317</td><td>For sperm purification</td></tr><tr><td>Ultracentrifuge</td><td>Beckman Coulter</td><td>Optima L-100XP</td><td>For sperm purification</td></tr><tr><td>50 ml centrifuge tube</td><td>Cellstar Greiner Bio-One</td><td>227261 or 210261</td><td>Oocyte collection and defolliculation reaction</td></tr><tr><td>15 ml centrifuge tube</td><td>FALCON</td><td>352097</td><td>For sperm purification</td></tr><tr><td>90 mm Petri dish&amp;nbsp;</td><td>Thermo Scientific</td><td>101VR20/C</td><td></td></tr><tr><td>Easy-Grip Cell Culture Dish, 60&amp;nbsp;x&amp;nbsp;15 mm</td><td>FALCON</td><td>353004</td><td></td></tr><tr><td>Easy-Grip Cell Culture Dish, 35&amp;nbsp;x&amp;nbsp;15 mm</td><td>FALCON</td><td>351008</td><td></td></tr></tbody></table>

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.

Embryonic development of ICSI embryos using in vitro matured oocytes was examined (Figure 3A). Maturation rates of GV oocytes to the MII stage are variable and largely depends on the oocyte quality. In good experiments, almost 100% of GV oocytes respond to progesterone and show signs of oocyte maturation, finally becoming eggs at the MII stage. All matured oocytes were subjected to ICSI and about 25% of injected eggs cleaved (Figure 3A, n = 13 for control scrambled oligo-injected oocytes and n = 7 for no oligo-injected oocytes). Approximately 60% or 80% of cleaved embryos, produced from control oligo-injected oocytes or non-injected oocyte, respectively, reached the blastula/gastrula stage. Among the blastula/gastrula embryos, approximately half of embryos in oligo-injected samples were of good quality (almost no signs of abnormal cleavage and apoptosis) whereas 82% of blastula/gastrula embryos were of good quality in non-injected samples (Figure 3A). Finally, 41% and 11% of cleaved embryos in oligo-injected samples reached the muscular response and the swimming tadpole stages, respectively, while 60% and 29% of cleaved embryos in non-injected samples did (Figure 3A). These ICSI embryos are the mixture of normal and abnormal embryos (Figure 3B). Some of them undergo metamorphosis and develop to mature frogs8. These results suggest that injection of antisense oligonucleotides into GV oocytes, followed by IVM and ICSI, allows efficient early embryonic development. Although the injection of antisense oligos itself decreases embryonic development, we are still able to obtain enough embryos for many experimental purposes such as checking developmental rates, RT-PCR, western blot and so on.
<img alt="Figure 1" src="/files/ftp_upload/52496/52496fig1highres.jpg" /> 
Figure 1: Typical examples of Xenopus laevis oocytes of good quality or bad quality for in vitro maturation experiments. (A) An example of bad quality oocytes. For example, oocytes showing patchy pigmentation are not used for subsequent experiments. Each Xenopus laevis oocyte is approximately 1.2-1.4 mm in diameter. (B) A partially defolliculated oocyte. The right half of the oocyte is covered by follicle cells, which can be discerned by the presence of blood vessels. An arrow shows an area free of follicle cells and into which the injection needle is injected. (C) An example of good quality oocytes, which are equally sized and show evenly pigmented animal hemispheres with clear contrast between the animal hemisphere and the vegetal hemisphere.
<img alt="Figure 2" src="/files/ftp_upload/52496/52496fig2highres.jpg" /> 
Figure 2: Xenopus laevis oocytes before and after maturation. After oocyte maturation, clear white spots appear at the top of animal hemispheres and follicle cells are peeled off. Each Xenopus laevis oocyte is approximately 1 mm in diameter.
<img alt="Figure 3" src="/files/ftp_upload/52496/52496fig3highres.jpg" /> 
Figure 3: Development of ICSI embryos, produced from in vitro matured oocytes. (A) Development of ICSI embryos to each stage is summarized. Oocytes were injected with control scrambled antisense oligonucleotides (control oligo injection) or without injection (non injection), followed by IVM and ICSI. The corresponding number of embryos at each stage is shown above the bars. Mean &#177; SEM is shown. N = 4-13 independent experiments/different females. (B) Examples of surviving ICSI embryos. These tailbud stage embryos were produced in one experiment, in which approximately 200 oocytes were used as a starting material.

Watch this Scientific Journal Video about Manipulation and In Vitro Maturation of Xenopus laevis Oocytes, Followed by Intracytoplasmic Sperm Injection, to Study Embryonic Development at JoVE.com

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.

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 ...

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Developmental Biology

22.4K Views.  University of Cambridge. 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.

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

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.

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.

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

Stem cell-like Xenopus Embryonic Explants to Study Early Neural Developmental Features In Vitro and In Vivo

Understanding the genetic programs underlying neural development is an important goal of developmental and stem cell biology. In the amphibian blastula, cells from the roof of the blastocoel are pluripotent. These cells can be isolated, and programmed to generate various tissues through manipulation of genes expression or induction by morphogens. In this manuscript protocols are described for the use of Xenopus laevis blastocoel roof explants as an assay system to investigate key in vivo and in vitro features of early neural development. These protocols allow the investigation of fate acquisition, cell migration behaviors, and cell autonomous and non-autonomous properties. The blastocoel roof explants can be cultured in a serum-free defined medium and grafted into host embryos. This transplantation into an embryo allows the investigation of the long-term lineage commitment, the inductive properties, and the behavior of transplanted cells in vivo. These assays can be exploited to investigate molecular mechanisms, cellular processes and gene regulatory networks underlying neural development. In the context of regenerative medicine, these assays provide a means to generate neural-derived cell types in vitro that could be used in drug screening.

Stem cell-like Xenopus Embryonic Explants to Study Early Neural Developmental Features In Vitro and In Vivo

In Xenopus embryos, cells from the roof of the blastocoel are pluripotent and can be programmed to generate various tissues. Here, we describe protocols to use amphibian blastocoel roof explants as an assay system to investigate key in vivo and in vitro features of early neural development.

Understanding the genetic programs underlying neural development is an important goal of developmental and stem cell biology. In the amphibian blastula, ...

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 ...

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 ...

Functional Manipulation of Maternal Gene Products Using In Vitro Oocyte Maturation in Zebrafish

Cellular events that take place during the earliest stages of animal embryonic development are driven by maternally derived gene products deposited into the developing oocyte. Because these events rely on maternal products which typically act very soon after fertilization-that preexist inside the egg, standard approaches for expression and functional reduction involving the injection of reagents into the fertilized egg are typically ineffective. Instead, such manipulations must be performed during oogenesis, prior to or during the accumulation of maternal products. This article describes in detail a protocol for the in vitro maturation of immature zebrafish oocytes and their subsequent in vitro fertilization, yielding viable embryos that survive to adulthood. This method allows the functional manipulation of maternal products during oogenesis, such as the expression of products for phenotypic rescue and tagged construct visualization, as well as the reduction of gene function through reverse-genetics agents.

Functional Manipulation of Maternal Gene Products Using In Vitro Oocyte Maturation in Zebrafish

An optimized protocol for the in vitro maturation of zebrafish oocytes used for the manipulation of maternal gene products is presented here.

Cellular events that take place during the earliest stages of animal embryonic development are driven by maternally derived gene products deposited into ...

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 Xenopus Laevis Oocytes

Microinjection of Xenopus laevis oocytes followed by thin-sectioning electron microscopy (EM) is an excellent system for studying nucleocytoplasmic transport. Because of its large nucleus and high density of nuclear pore complexes (NPCs), nuclear transport can be easily visualized in the Xenopus oocyte. Much insight into the mechanisms of nuclear import and export has been gained through use of this system (reviewed by Pant&eacute;, 2006). In addition, we have used microinjection of Xenopus oocytes to dissect the nuclear import pathways of several viruses that replicate in the host nucleus. 
Here we demonstrate the cytoplasmic microinjection of Xenopus oocytes with a nuclear import substrate. We also show preparation of the injected oocytes for visualization by thin-sectioning EM, including dissection, dehydration, and embedding of the oocytes into an epoxy embedding resin. Finally, we provide representative results for oocytes that have been microinjected with the capsid of the baculovirus Autographa californica nucleopolyhedrovirus (AcMNPV) or the parvovirus Minute Virus of Mice (MVM), and discuss potential applications of the technique.

Here we demonstrate cytoplasmic microinjection of Xenopus laevis oocytes with a nuclear import substrate, as well as preparation of the injected oocytes for visualization by thin-sectioning electron microscopy.

Microinjection of Xenopus laevis oocytes followed by thin-sectioning electron microscopy (EM) is an excellent system for studying nucleocytoplasmic ...

Biology

Fertilization of Xenopus oocytes using the Host Transfer Method

Studying the contribution of maternally inherited molecules to vertebrate early development is often hampered by the time and expense necessary to generate maternal-effect mutant animals. Additionally, many of the techniques to overexpress or inhibit gene function in organisms such as Xenopus and zebrafish fail to sufficiently target critical maternal signaling pathways, such as Wnt signaling. In Xenopus, manipulating gene function in cultured oocytes and subsequently fertilizing them can ameliorate these problems to some extent. Oocytes are manually defolliculated from donor ovary tissue, injected or treated in culture as desired, and then stimulated with progesterone to induce maturation. Next, the oocytes are introduced into the body cavity of an ovulating host female frog, whereupon they will be translocated through the host's oviduct and acquire modifications and jelly coats necessary for fertilization. The resulting embryos can then be raised to the desired stage and analyzed for the effects of any experimental perturbations. This host-transfer method has been highly effective in uncovering basic mechanisms of early development and allows a wide range of experimental possibilities not available in any other vertebrate model organism.

Fertilization of Xenopus oocytes using the Host Transfer Method

Procedure for fertilizing Xenopus oocytes by the host transfer method.

Studying the contribution of maternally inherited molecules to vertebrate early development is often hampered by the time and expense necessary to ...

Live-cell Imaging and Quantitative Analysis of Embryonic Epithelial Cells in Xenopus laevis

Embryonic epithelial cells serve as an ideal model to study morphogenesis where multi-cellular tissues undergo changes in their geometry, such as changes in cell surface area and cell height, and where cells undergo mitosis and migrate. Furthermore, epithelial cells can also regulate morphogenetic movements in adjacent tissues1. A traditional method to study epithelial cells and tissues involve chemical fixation and histological methods to determine cell morphology or localization of particular proteins of interest. These approaches continue to be useful and provide "snapshots" of cell shapes and tissue architecture, however, much remains to be understood about how cells acquire specific shapes, how various proteins move or localize to specific positions, and what paths cells follow toward their final differentiated fate. High resolution live imaging complements traditional methods and also allows more direct investigation into the dynamic cellular processes involved in the formation, maintenance, and morphogenesis of multicellular epithelial sheets. Here we demonstrate experimental methods from the isolation of animal cap tissues from Xenopus laevis embryos to confocal imaging of epithelial cells and simple measurement approaches that together can augment molecular and cellular studies of epithelial morphogenesis.

Live-cell Imaging and Quantitative Analysis of Embryonic Epithelial Cells in Xenopus laevis

Xenopus embryonic epithelia are an ideal model system to study cell behaviors such as polarity development and shape change during epithelial morphogenesis. Traditional histology of fixed samples is increasingly being complemented by live-cell confocal imaging. Here we demonstrate methods to isolate frog tissues and visualize live epithelial cells and their cytoskeleton using live-cell confocal microscopy.

Embryonic epithelial cells serve as an ideal model to study morphogenesis where multi-cellular tissues undergo changes in their geometry, such as changes ...

Production of Transgenic Xenopus laevis by Restriction Enzyme Mediated Integration and Nuclear Transplantation

Stable integration of cloned gene products into the Xenopus genome is necessary to control the time and place of expression, to express genes at later stages of embryonic development, and to define how enhancers and promoters regulate gene expression within the embryo. The protocol demonstrated here can be used to efficiently produce transgenic Xenopus laevis embryos. This transgenesis approach involves three parts: 1. Sperm nuclei are isolated from adult X. laevis testis by treatment with lysolecithin, which permeabilizes the sperm plasma membrane. 2. Egg extract is prepared by low speed centrifugation, addition of calcium to cause the extract to progress to interphase of the cell cycle, and a high-speed centrifugation to isolate interphase cytosol. 3. Nuclear transplantation: the nuclei and extract are combined with the linearized plasmid DNA to be introduced as the transgene and a small amount of restriction enzyme. During a short reaction, egg extract partially decondenses the sperm chromatin and the restriction enzyme generates chromosomal breaks that promote recombination of the transgene into the genome. The treated sperm nuclei are then transplanted into unfertilized eggs. Integration of the transgene usually occurs prior to the first embryonic cleavage such that the resulting embryos are not chimeric. These embryos can be analyzed without any need to breed to the next generation, allowing for efficient and rapid generation of transgenic embryos for analyses of promoter and gene function. Adult X. laevis resulting from this procedure also propagate the transgene through the germline and can be used to generate lines of transgenic animals for multiple purposes.

Production of Transgenic Xenopus laevis by Restriction Enzyme Mediated Integration and Nuclear Transplantation

This video protocol demonstrates a method for generating transgenic Xenopus laevis by introduction of transgenes into sperm nuclei followed by nuclear transplantation into unfertilized eggs.

Stable integration of cloned gene products into the Xenopus genome is necessary to control the time and place of expression, to express genes at later ...

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

Summary

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Chapters in this video

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

Stem cell-like Xenopus Embryonic Explants to Study Early Neural Developmental Features In Vitro and In Vivo

Functional Cloning Using a Xenopus Oocyte Expression System

Technique to Target Microinjection to the Developing Xenopus Kidney

Functional Manipulation of Maternal Gene Products Using In Vitro Oocyte Maturation in Zebrafish

Visualization and Quantitative Analysis of Embryonic Angiogenesis in Xenopus tropicalis

Microinjection of Xenopus Laevis Oocytes

Fertilization of Xenopus oocytes using the Host Transfer Method

Live-cell Imaging and Quantitative Analysis of Embryonic Epithelial Cells in Xenopus laevis

Production of Transgenic Xenopus laevis by Restriction Enzyme Mediated Integration and Nuclear Transplantation