Name: functional cloning using a xenopus oocyte expression system
Uploaded: 2016-01-30T14:00:00
Description: Watch this Scientific Journal Video about Functional Cloning Using a Xenopus Oocyte Expression System at JoVE.com

This work was supported by a Professional Development Grant to C.Z.P. from the Shepherd University Foundation. The authors wish to thank Brett Zirkle and Malia Deshotel for helpful discussions on the protocols, and Dr. Carol Hurney for generous assistance.

All experimental procedures were approved by the University of Virginia Institutional Animal Care and Use Committee.
Note: Figure 1 shows a schematic overview of the experimental procedures.
1. Preparation of Oocytes
<ol>
	<li>Pre-prime X. laevis females with 150 U of Pregnant Mare Serum Gonadotropin (PMSG) approximately one week in advance of oocyte isolation. Inject 1 ml 150 U/ml PMSG into dorsal lymph sac with 1 cc ste...

<ol>
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The method described here for the functional cloning of genes capable of inducing a response in competent ectoderm can be used to identify a wide range of gene products. This method expands upon past work by combining tissue-inducing assays with expression cloning techniques. We utilize the metabolic pathways of the Xenopus oocyte as a source of production of inducing factors, directly or indirectly, following RNA injection. This, in combination with the use of established methods for cloning a gene of interest<...

Forward genetic approaches to identify genes of interest through their function or loss-of-function1,2 are an integral part of understanding complex patterning events in development. Coupled with powerful reverse genetic techniques available to an ever-widening array of systems and researchers3-5, it is now possible to identify genes with a key functional role in a pathway and then elucidate that function at the cellular level and in interaction with other gene products. One approach to functionally identifying genes of interest that has yielded many key findings in the past is expression cloning6,7.
Our recent aim8 was to identify early lens-inductive factors, since it has been demonstrated that initial steps in the vertebrate lens-inductive process occur as early as gastrula stages. To that end, we used the transiently lens-competent9 animal cap ectoderm (stage 11-11.510) of Xenopus embryos as responding tissue for induction, and the stage VI Xenopus oocyte as a source of production for the inducing factors.
The following protocol builds on the expression cloning and sib selection protocols of Smith and Harland6,7, also successfully used by others11-13. In our oocyte expression system (first utilized for production of inducing factors by Lustig and Kirschner14), pools of injected transcripts capable of directly or indirectly causing the oocytes to produce factors that elicit a lens-inductive response in animal cap ectoderm are selected for and identified. Since the system is useful for expressing secreted inducing molecules directly (oocyte-injected INHBB mRNA causes mesoderm induction in mesoderm-competent animal cap ectoderm8), we originally expected the screening procedure to be useful chiefly for identification of paracrine factors. However, since we identified a nuclear factor in our screen (ldb18), it is clear that the system can be used to identify a wide variety of molecules such as transcriptional or translational regulatory factors, miRNAs, cofactors, or juxtacrine factors.

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			<td height="42" style="height:42px;width:207px;">Programmable Puller</td>
			<td style="width:191px;">World Precision Instruments</td>
			<td style="width:135px;">PUL-1000</td>
			<td style="width:233px;">Micropipette needle puller</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:207px;">Proteinase K</td>
			<td style="width:191px;">Sigma</td>
			<td style="width:135px;">P6556</td>
			<td style="width:233px;">for ISH</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:207px;">pTnT Vector</td>
			<td style="width:191px;">Promega</td>
			<td style="width:135px;">L5610</td>
			<td style="width:233px;">cDNA library construction</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:207px;">Riboprobe Combination System</td>
			<td style="width:191px;">Promega</td>
			<td style="width:135px;">P1450</td>
			<td style="width:233px;">in vitro transcription</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:207px;">Superscript Full Length cDNA Library Construction Kit</td>
			<td style="width:191px;">Life Technologies</td>
			<td style="width:135px;">18248013</td>
			<td style="width:233px;">kit for cDNA library construction</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:207px;">Sutures, 3-0 silk</td>
			<td style="width:191px;">Fisher Scientific</td>
			<td style="width:135px;">19-037-516</td>
			<td style="width:233px;">Suture thread and needle for post-oocyte removal</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:207px;">Torula RNA</td>
			<td style="width:191px;">Sigma</td>
			<td style="width:135px;">R3629</td>
			<td style="width:233px;">for ISH</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:207px;">Triethanolamine</td>
			<td style="width:191px;">Sigma</td>
			<td style="width:135px;">T1502</td>
			<td style="width:233px;">for ISH</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:207px;">Tween 20</td>
			<td style="width:191px;">Sigma</td>
			<td style="width:135px;">P9416</td>
			<td style="width:233px;">for ISH</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:207px;">Universal RiboClone cDNA Synthesis System</td>
			<td style="width:191px;">Promega</td>
			<td style="width:135px;">C4360</td>
			<td style="width:233px;">alternative kit for cDNA library construction</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:207px;">Xenopus Full ORF Entry Clones - ORFeome Collaboration</td>
			<td style="width:191px;">Source Bioscience</td>
			<td style="width:135px;">5055_XenORFeome</td>
			<td style="width:233px;">ORFeome Clones</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:207px;">XL2-Blue Ultracompetent Cells</td>
			<td style="width:191px;">Agilent Technologies</td>
			<td style="width:135px;">200150</td>
			<td style="width:233px;">cells for transformation of cDNA library</td>
		</tr>
	</tbody>
</table>

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.

In response to expression of mRNA injected into oocytes, responding animal cap tissue was assayed for expression of otx2 by in situ hybridization (Figure 2 and Table 1); otx2 is expressed in the presumptive lens ectoderm (PLE) from neural tube closure through lens placode thickening19. However, since otx2 is also expressed in the anterior neural ectoderm as well as non-neural head ectoderm outside the PLE, it is associated wi...

Watch this Scientific Journal Video about Functional Cloning Using a Xenopus Oocyte Expression System at JoVE.com

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.

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 ...

The overall goal of this procedure is to demonstrate a Xenopus oocyte, an animal cap system, suitable for the identification of gene products capable of inducing a response in competent ectoderm. This method can help answer key questions in the field of developmental biology such as what genes are necessary to illicit an inductive response. The main advantage of this technique is its use of the Xenopus oocyte, as an expression system, to produce and identify inducers acting upon a target tissue, or even genes acting upstream of inducers.Visual demonstration of this method is extremely useful, as the dissection and recombination steps are highly stage dependent and require a refined technique. After collecting ovarian tissue from anesthetized female frogs, tear the tissue into small pieces, each containing approximately 10 to 20 oocytes. And transfer these fragments, first to fresh OR2-solution, and then to OR2-containing 2.0 milligrams per milliliter collagenase A.Continue by gently agitating the tissue-containing mixture on a shaker for one hour.Then transfer the fragments to fresh collagenase solution, and agitate for an additional hour. Expect to observe deflocculated oocytes at the end of this treatment. Proceed to wash the oocytes 10 times in complete OR2, and then twice in oocyte culture medium, abbreviated as OCM.Afterwards, place the oocytes in fresh OCM, and visually inspect them under a dissection microscope. Isolate those at stage six by discarding the smaller, immature oocytes. Next, place the oocytes in an agarose-coated Petri dish containing OCM, and maintain them at 18 to 20 degrees Celsius until injection.To prepare for microinjection, place glass capillary tubing into a needle puller, pull it, and then break the tips off the glass to generate needles approximately 20 micrometers in diameter. On a compound microscope, measure the needle tips with a calibrated ocular micrometer. Next, push clay into a uniform layer on the bottom of a 35 by 10 millimeter Petri dish.And then create parallel grooves in this layer, using a mall probe-like tool. Fill the clay-lined dish with approximately 2 milliliters of 3%Ficoll in 1x modified Barth's saline, or MBS. And then transfer the oocytes to it, using a wide-bore pipette.Position the oocytes in the groves so they will be held in place during the subsequent microinjection. Using a microinjector, fill a needle with approximately two microliters of a previously generated pool of mRNA and adjust the balance to produce slight positive pressure, which will prevent oocyte cytoplasm from being drawn into the needle during injection. Then, inject each oocyte with 20 nanoliters of RNA in the equatorial region.Afterwards, leave the oocytes in the Ficoll MBS for one hour, and then gently transfer them to 1x MBS. Proceed to incubate the oocytes for eight to 24 hours at 20 degrees Celsius. To begin the animal cap assay, gather 3/4x normal amphibian medium, abbreviated as NAM solution, fine forceps, a hairloop, previously injected oocytes, and xenopus embryos at stage 11 to 11.5.Then, break apart glass cover slips into fragments approximately one millimeters by two millimeters in size, and pass these pieces through a flame until their edges polish and drew. Next, press clay into a single layer in a dish, as previously described. And use a mall probe to create individual cup-shaped impressions in this coating.Proceed to fill the dish with approximately two milliliters of 3/4x NAM. And to it, transfer the injected oocytes, positioning several so that each is immobilized in a single indentation. To ready the embryos, transfer them in a dish containing 3/4x NAM solution.Select a subset of gastrula to be used as staging controls for the age of the ectoderm, and transfer them to another dish containing the same solution. And set this plate aside. For embryos that will be used in the animal cap assey, remove their vitelline membranes with two pairs of fine forceps.Afterwards, transfer the gastrula to the clay-lined dish with the oocytes. To begin, cut the animal caps from the embryos using two pairs of fine foreceps, being careful to avoid the equatorial tissue. To generate recombinants using the first method, position an animal caps so that the inner surface contacts the animal hemisphere of an oocyte, already positioned in an indentation.And repeat this process for several of the injected oocytes. To ensure that these recombinants are held together, place a curved glass coverslip fragment on top of each of them, and apply downward pressure until the animal is flattened and the coverslip contacts the clay. To generate recombinants using the second method, place animal caps and oocytes together in empty individual indentations in the clay.And ensure the animal caps inner surfaces are facing the oocyte. Then, secure the two tissues together using small extensions of clay. Once multiple recombinants have been generated using either method, culture then and the set-aside control embryos at 20 degrees celsius.When the control embryos reach the desired stage, remove the coverslips from the recombinants and isolate the animal cap ectoderm using forceps and a hair loop. Proceed to fix both ectodermal fragments and control embryos in MEMFA for one hour. And transfer them to ethanol and store this tissue at negative 20 degrees celsius.Here, sets of oocytes were injected with pools of mRNA corresponding to progressively smaller numbers of clones or colonies, and then, cultured with animal caps. Subsequently, the number of animal caps in each set expressing foxe3, a marker normally observed in presumptive lens ectoderm from early neural plate stages to vesicle formation, and use here, to evaluate lens inducing capability, was determined. This method identified in nuclear factor encoding gene, ldb1, which can produce a lens-inducing response in 50 out of 179, or 28%of animal caps assessed.Shown here, our in situ hybridization images, depicting foxe3 signal, indicated by arrow heads, in animal caps cultured with ldb1 injected oocytes from roughly stage 11 to stage 23. No foxe3 expression is observed in corresponding control animal caps placed on uninjected oocytes. When sections were generated from these animal caps, foxe3 expression was observed in both the inner and outer ectodermal layers.Expression in the inner layer is characteristic of a lens response. Or, as signaled in both layers, is indicative of other structures such as the olfactory placode. Following this procedure, methods like immunohistochemistry, in situ hybridization, or direct detection of a fluorescent reporter gene, can be performed in order to assess an inductive response in the animal cap ectoderm.

functional-cloning-using-a-xenopus-oocyte-expression-system

Research

JoVE Journal

Developmental Biology

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 ...

Live Imaging of Innate Immune and Preneoplastic Cell Interactions Using an Inducible Gal4/UAS Expression System in Larval Zebrafish Skin

Here we describe a method to conditionally induce epithelial cell transformation by the use of the 4-Hydroxytamoxifen (4-OHT) inducible KalTA4-ERT2/UAS expression system1 in zebrafish larvae, and the subsequent live imaging of innate immune cell interaction with HRASG12V expressing skin cells. The KalTA4-ERT2/UAS system is both inducible and reversible which allows us to induce cell transformation with precise temporal/spatial resolution in vivo. This provides us with a unique opportunity to live image how individual preneoplastic cells interact with host tissues as soon as they emerge, then follow their progression as well as regression. Recent studies in zebrafish larvae have shown a trophic function of innate immunity in the earliest stages of tumorigenesis2,3. Our inducible system would allow us to live image the onset of cellular transformation and the subsequent host response, which may lead to important insights on the underlying mechanisms for the regulation of oncogenic trophic inflammatory responses. We also discuss how one might adapt our protocol to achieve temporal and spatial control of ectopic gene expression in any tissue of interest.

Studying the earliest events of preneoplastic cell progression and innate immune cell interaction is pivotal to understand and treat cancer. Here we describe a method to conditionally induce epithelial cell transformations and the subsequent live imaging of innate immune cell interaction with HRASG12V expressing skin cells in zebrafish larvae.

Here we describe a method to conditionally induce epithelial cell transformation by the use of the 4-Hydroxytamoxifen (4-OHT) inducible KalTA4-ERT2/UAS ...

Alginate Encapsulation of Pluripotent Stem Cells Using a Co-axial Nozzle

Pluripotent stem cells (PS cells) are the focus of intense research due to their role in regenerative medicine and drug screening. However, the development of a mass culture system would be required for using PS cells in these applications. Suspension culture is one promising culture method for the mass production of PS cells, although some issues such as controlling aggregation and limiting shear stress from the culture medium are still unsolved. In order to solve these problems, we developed a method of calcium alginate (Alg-Ca) encapsulation using a co-axial nozzle. This method can control the size of the capsules easily by co-flowing N2 gas. The controllable capsule diameter must be larger than 500 &#181;m because too high a flow rate of N2 gas causes the breakdown of droplets and thus heterogeneous-sized capsules. Moreover, a low concentration of Alg-Na and CaCl2 causes non-spherical capsules. Although an Alg-Ca capsule without a coating of Alg-PLL easily dissolves enabling the collection of cells, they can also potentially leak out from capsules lacking an Alg-PLL coating. Indeed, an alginate-PLL coating can prevent cellular leakage but is also hard to break. This technology can be used to research the stem cell niche as well as the mass production of PS cells because encapsulation can modify the micro-environment surrounding cells including the extracellular matrix and the concentration of secreted factors.

We established a method of encapsulating pluripotent stem cells (PS cells) into alginate hydrogel capsules using a co-axial nozzle. This prevents cells from aggregating excessively and limits the shear stress experienced by cells in suspension culture. The technique is applicable to the mass production of PS cells as well as research on stem cell niche.

Pluripotent stem cells (PS cells) are the focus of intense research due to their role in regenerative medicine and drug screening.  However, the ...

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 ...

Tracking Cells in GFP-transgenic Zebrafish Using the Photoconvertible PSmOrange System

The rapid development of transparent zebrafish embryos (Danio rerio) in combination with fluorescent labelings of cells and tissues allows visualizing developmental processes as they happen in the living animal. Cells of interest can be labeled by using a tissue specific promoter to drive the expression of a fluorescent protein (FP) for the generation of transgenic lines. Using fluorescent photoconvertible proteins for this purpose additionally allows to precisely follow defined structures within the expression domain. Illuminating the protein in the region of interest, changes its emission spectrum and highlights a particular cell or cell cluster leaving other transgenic cells in their original color. A major limitation is the lack of known promoters for a large number of tissues in the zebrafish. Conversely, gene- and enhancer trap screens have generated enormous transgenic resources discretely labeling literally all embryonic structures mostly with GFP or to a lesser extend red or yellow FPs. An approach to follow defined structures in such transgenic backgrounds would be to additionally introduce a ubiquitous photoconvertible protein, which could be converted in the cell(s) of interest. However, the photoconvertible proteins available involve a green and/or less frequently a red emission state1 and can therefore often not be used to track cells in the FP-background of existing transgenic lines. To circumvent this problem, we have established the PSmOrange system for the zebrafish2,3. Simple microinjection of synthetic mRNA encoding a nuclear form of this protein labels all cell nuclei with orange/red fluorescence. Upon targeted photoconversion of the protein, it switches its emission spectrum to far red. The quantum efficiency and stability of the protein makes PSmOrange a superb cell-tracking tool for zebrafish and possibly other teleost species.

We established the photoconvertible PSmOrange system as a powerful, straight-forward and cost inexpensive tool for in vivo cell tracking in GFP transgenic backgrounds. This protocol describes its application in the zebrafish model system.

The rapid development of transparent zebrafish embryos (Danio rerio) in combination with fluorescent labelings of cells and tissues allows visualizing ...

Temporal Ordering of Dynamic Expression Data from Detailed Spatial Expression Maps

During somitogenesis, pairs of epithelial somites form in a progressive manner, budding off from the anterior end of the pre-somitic mesoderm (PSM) with a strict species-specific periodicity. The periodicity of the process is regulated by a molecular oscillator, known as the "segmentation clock," acting in the PSM cells. This clock drives the oscillatory patterns of gene expression across the PSM in a posterior-anterior direction. These so-called clock genes are key components of three signaling pathways: Wnt, Notch, and fibroblast growth factor (FGF). In addition, Notch signaling is essential for synchronizing intracellular oscillations in neighboring cells. We recently gained insight into how this may be mechanistically regulated. Upon ligand activation, the Notch receptor is cleaved, releasing the intracellular domain (NICD), which moves to the nucleus and regulates gene expression. NICD is highly labile, and its phosphorylation-dependent turnover acts to restrict Notch signaling. The profile of NICD production (and degradation) in the PSM is known to be oscillatory and to resemble that of a clock gene. We recently reported that both the Notch receptor and the Delta ligand, which mediate intercellular coupling, themselves exhibit dynamic expression at both the mRNA and protein levels. In this article, we describe the sensitive detection methods and detailed image analysis tools that we used, in combination with the computational modeling that we designed, to extract and overlay expression data from distinct points in the expression cycle. This allowed us to construct a spatio-temporal picture of the dynamic expression profile for the receptor, the ligand, and the Notch target clock genes throughout an oscillation cycle. Here, we describe the protocols used to generate and culture the PSM explants, as well as the procedure to stain for the mRNA or protein. We also explain how the confocal images were subsequently analyzed and temporally ordered computationally to generate ordered sequences of clock expression snapshots, hereafter defined as "kymographs," for the visualization of the spatiotemporal expression of Delta-like1 (Dll1) and Notch1 throughout the PSM.

The segmentation clock drives oscillatory gene expression across the pre-somitic mesoderm (PSM). Dynamic Notch activity is key to this process. We use imaging and computational analyses to extract temporal dynamics from spatial expression data to demonstrate that Delta ligand and Notch receptor expression oscillate in the vertebrate PSM.

During somitogenesis, pairs of epithelial somites form in a progressive manner, budding off from the anterior end of the pre-somitic mesoderm (PSM) with a ...

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 ...

Fetal Mouse Cardiovascular Imaging Using a High-frequency Ultrasound (30/45MHZ) System

Congenital heart defects (CHDs) are the most common cause of childhood morbidity and early mortality. Prenatal detection&#160;of the underlying molecular mechanisms of CHDs is&#160;crucial for inventing new preventive and therapeutic strategies. Mutant mouse models are powerful tools to discover new&#160;mechanisms&#160;and environmental stress modifiers that drive cardiac development and their potential&#160;alteration in CHDs. However, efforts to establish the causality of these putative contributors have been limited to histological&#160;and molecular studies&#160;in non-survival animal experiments, in which&#160;monitoring the key physiological and hemodynamic parameters is&#160;often absent. Live imaging technology has become an essential tool to establish the&#160;etiology of CHDs. In particular,&#160;ultrasound imaging can be used prenatally without surgically exposing the fetuses,&#160;allowing maintaining&#160;their baseline physiology while monitoring the impact of environmental stress&#160;on the hemodynamic and structural aspects of cardiac chamber development. Herein, we use the High-Frequency Ultrasound (30/45)&#160;system to examine the cardiovascular system in fetal mice at E18.5 in utero at the baseline and in response to prenatal hypoxia exposure. We demonstrate the feasibility of the system to measure cardiac chamber size, morphology, ventricular function, fetal heart rate, and umbilical artery flow indices, and their alterations in fetal mice exposed to systemic chronic hypoxia in utero in real time.

Fetal Mouse Cardiovascular Imaging Using a High-frequency Ultrasound 30/45MHZ System

High-frequency ultrasound imaging of the fetal mouse has improved imaging resolution and can provide precise non-invasive characterization of cardiac development and structural defects. The protocol outlined herein is designed to perform real-time fetal mice echocardiography in vivo.

Congenital heart defects (CHDs) are the most common cause of childhood morbidity and early mortality. Prenatal detection&#160;of the underlying molecular ...

Three-dimensional Angiogenesis Assay System using Co-culture Spheroids Formed by Endothelial Colony Forming Cells and Mesenchymal Stem Cells

Studies in the field of angiogenesis have been aggressively growing in the last few decades with the recognition that angiogenesis is a hallmark of more than 50 different pathological conditions, such as rheumatoid arthritis, oculopathy, cardiovascular diseases, and tumor metastasis. During angiogenesis drug development, it is crucial to use in vitro assay systems with appropriate cell types and proper conditions to reflect the physiologic angiogenesis process. To overcome limitations of current in vitro angiogenesis assay systems using mainly endothelial cells, we developed a 3-dimensional (3D) co-culture spheroid sprouting assay system. Co-culture spheroids were produced by two human vascular cell precursors, endothelial colony forming cells (ECFCs) and mesenchymal stem cells (MSCs) with a ratio of 5 to 1. ECFCs+MSCs spheroids were embedded into type I collagen matrix to mimic the in vivo extracellular environment. A real-time cell recorder was utilized to continuously observe the progression of angiogenic sprouting from spheroids for 24 h. Live cell fluorescent labeling technique was also applied to tract the localization of each cell type during sprout formation. Angiogenic potential was quantified by counting the number of sprouts and measuring the cumulative length of sprouts generated from the individual spheroids. Five randomly-selected spheroids were analyzed per experimental group. Comparison experiments demonstrated that ECFCs+MSCs spheroids showed greater sprout number and cumulative sprout length compared with ECFCs-only spheroids. Bevacizumab, an FDA-approved angiogenesis inhibitor, was tested with the newly-developed co-culture spheroid assay system to verify its potential to screen anti-angiogenic drugs. The IC50 value for ECFCs+MSCs spheroids compared to the ECFCs-only spheroids was closer to the effective plasma concentration of bevacizumab obtained from the xenograft tumor mouse model. The present study suggests that the 3D ECFCs+MSCs spheroid angiogenesis assay system is relevant to physiologic angiogenesis, and can predict an effective plasma concentration in advance of animal experiments.

Three-dimensional co-culture spheroid angiogenesis assay system is designed to mimic the physiologic angiogenesis. Co-culture spheroids are formed by two human vascular cell precursors, ECFCs and MSCs, and embedded in collagen gel. The new system is effective for evaluating angiogenic modulators, and provides more relevant information to the in vivo study.

Studies in the field of angiogenesis have been aggressively growing in the last few decades with the recognition that angiogenesis is a hallmark of more ...

Defining the Program of Maternal mRNA Translation during In vitro Maturation using a Single Oocyte Reporter Assay

Events associated with oocyte nuclear maturation have been well described. However, much less is known about the molecular pathways and processes that take place in the cytoplasm in preparation for fertilization and acquisition of totipotency. During oocyte maturation, changes in gene expression depend exclusively on the translation and degradation of maternal messenger RNAs (mRNAs) rather than on transcription. Execution of the translational program, therefore, plays a key role in establishing oocyte developmental competence to sustain embryo development. This paper is part of a focus on defining the program of maternal mRNA translation that takes place during meiotic maturation and at the oocyte-to-zygote transition. In this method paper, a strategy is presented to study the regulation of translation of target mRNAs during in vitro oocyte maturation. Here, a Ypet reporter is fused to the 3&#39; untranslated region (UTR) of the gene of interest and then micro-injected into oocytes together with polyadenylated mRNA encoding for mCherry to control for injected volume. By using time-lapse microscopy to measure reporter accumulation, translation rates are calculated at different transitions during oocyte meiotic maturation. Here, the protocols for oocyte isolation and injection, time-lapse recording, and data analysis have been described, using the Ypet/interleukin-7 (IL-7)-3&#39; UTR reporter as an example.

This protocol describes a reporter assay to study the regulation of mRNA translation in single oocytes during in vitro maturation.

Events associated with oocyte nuclear maturation have been well described. However, much less is known about the molecular pathways and processes that ...