Name: analysis of transforming growth factor &#223; family cleavage products secreted into the blastocoele of xenopus laevis embryos
Uploaded: 2021-07-21T15:00:00
Description: Watch this Scientific Journal Video about Analysis of Transforming Growth Factor ÃŸ Family Cleavage Products Secreted Into the Blastocoele of Xenopus laevis Embryos at JoVE.com

We thank Mary Sanchez for excellent animal care. The authors&#39; research is supported by the National Institute of Child Health and Human Development of the National Institutes of Health (NIH/NICHD) grants R01HD067473-08 and R21 HD102668-01 and by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK/NIH) grant R01DK128068-01.

All procedures described are approved by the Institutional Animal Care and Use Committee (IACUC) of the University of Utah. Frogs are housed in an IACUC approved facility. Male frogs are euthanized by immersion in tricaine following by clipping the ventricle of the heart. Female frogs are housed in the laboratory for a maximum of 24 h following hormonal induction of spawning to allow for egg collection and then returned to the care facility.
1. Collection of X. laevis Testes
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C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mutation+of+an+upstream+cleavage+site+in+the+BMP4+prodomain+leads+to+tissue-specific+loss+of+activity.">Mutation of an upstream cleavage site in the BMP4 prodomain leads to tissue-specific loss of activity.</a> Development. 133 (10), 1933-1942 (2006).</li><li>Le Good, J. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nodal+stability+determines+signaling+range.">Nodal stability determines signaling range.</a> Current Biology. 15 (1), 31-36 (2005).</li><li>Tilak, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simultaneous+rather+than+ordered+cleavage+of+two+sites+within+the+BMP4+prodomain+leads+to+loss+of+ligand+in+mice.">Simultaneous rather than ordered cleavage of two sites within the BMP4 prodomain leads to loss of ligand in mice.</a> Development. 141 (15), 3062-3071 (2014).</li><li>Neugebauer, J. 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L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Site-specific+cleavage+of+BMP4+by+furin,+PC6,+and+PC7.">Site-specific cleavage of BMP4 by furin, PC6, and PC7.</a> Journal of Biological Chemistry. 284 (40), 27157-27166 (2009).</li><li>Birsoy, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=XPACE4+is+a+localized+pro-protein+convertase+required+for+mesoderm+induction+and+the+cleavage+of+specific+TGFbeta+proteins+in+Xenopus+development.">XPACE4 is a localized pro-protein convertase required for mesoderm induction and the cleavage of specific TGFbeta proteins in Xenopus development.</a> Development. 132 (3), 591-602 (2005).</li><li>Mimoto, M. S., Christian, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Manipulation+of+gene+function+in+Xenopus+laevis.">Manipulation of gene function in Xenopus laevis.</a> Methods Mol Biol. 770, 55-75 (2011).</li><li>Nelsen, S., Berg, L., Wong, C., Christian, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Proprotein+convertase+genes+in+Xenopus+development.">Proprotein convertase genes in Xenopus development.</a> Developmental Dynamics. 233 (3), 1038-1044 (2005).</li><li>Constam, D. B., Robertson, E. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+of+bone+morphogenetic+protein+activity+by+pro+domains+and+proprotein+convertases.">Regulation of bone morphogenetic protein activity by pro domains and proprotein convertases.</a> Journal of Cell Biology. 144 (1), 139-149 (1999).</li><li>Sopory, S., Nelsen, S. M., Degnin, C., Wong, C., Christian, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regulation+of+bone+morphogenetic+protein-4+activity+by+sequence+elements+within+the+prodomain.">Regulation of bone morphogenetic protein-4 activity by sequence elements within the prodomain.</a> Journal of Biological Chemistry. 281 (45), 34021-34031 (2006).</li><li>Sopory, S., Christian, J. L., Whitman, M. A., Whitman, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Analysis of Growth Factor Signaling in Embryos. , 38-55 (2006).</li><li>Kim, H. S., McKnite, A., Christian, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Proteolytic+Activation+of+Bmps:+Analysis+of+Cleavage+in+Xenopus+Oocytes+and+Embryos.">Proteolytic Activation of Bmps: Analysis of Cleavage in Xenopus Oocytes and Embryos.</a> Methods in Molecular Biology. 1891, 115-133 (2019).</li><li>Degnin, C., Jean, F., Thomas, G., Christian, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cleavages+within+the+prodomain+direct+intracellular+trafficking+and+degradation+of+mature+bone+morphogenetic+protein-4.">Cleavages within the prodomain direct intracellular trafficking and degradation of mature bone morphogenetic protein-4.</a> Molecular Biology of the Cell. 15 (11), 5012-5020 (2004).</li></ol>

The main advantages to the protocol described here are that it can be completed relatively quickly, does not require expensive reagents and provides a source of concentrated Tgf&#223; cleavage products under physiologic conditions. Another advantage is that it allows one to analyze epitope-tagged proteins and thus circumvent the shortage of commercially available antibodies that recognize most Tgf&#223; family prodomain. Although it is also possible to analyze the cleavage of epitope-tagged Tgf&#223; precursor proteins i...

Members of the Transforming Growth Factor &#223; (Tgf&#223;) superfamily are synthesized as inactive, dimerized precursor proteins. The precursors are then cleaved by members of the proprotein convertase (PC) family, either within the secretory pathway or outside of cells. This creates an active, disulfide-bonded ligand dimer and two prodomain fragments1. Although it has been known for over 30 years that the prodomain of Tgf&#223; family precursors is required to generate an active ligand2, the understanding of how prodomains contribute to ligand function is incomplete.
Although the understanding of the process of proteolytic activation of Tgf&#223; family members remains incomplete, there is increasing interest in understanding which PC consensus motif(s) are cleaved in vivo, whether the cleavage occurs in a specific subcellular or extracellular compartment, and whether the prodomain remains covalently or noncovalently associated with the cleaved ligand3. Several studies have shown that the prodomain not only guides ligand folding before cleavage4,5, but can also influence growth factor stability and range of action6,7,8,9, drive the formation of homodimers or heterodimers10, anchor the ligand in the extracellular matrix to maintain ligand latency11, and in some cases, function as a ligand in its own right to activate heterologous signaling12. Heterozygous point mutations within the prodomain of many members of the Tgf&#223; family are associated with eye, bone, kidney, skeletal or other defects in humans3. These findings highlight the critical role of the prodomain in generating and maintaining an active ligand and stress the importance of identifying and deciphering the role of cleavage products developed during proteolytic maturation of Tgf&#223; family precursors.
Here we describe a detailed protocol for aspirating cleavage products generated during maturation of Tgf&#223; family precursors from the blastocoele of X. laevis embryos and then analyzing them on immunoblots. This protocol can be used to determine whether one or more PC consensus motif(s) in a precursor protein are cleaved in vivo10,13, identify the endogenous PC(s) that cleave each motif13,14, compare in vivo formation of Tgf&#223; family homodimers versus heterodimers10 or analyze whether human disease-associated point mutations in Tgf&#223; precursors impact their ability to form functional dimeric ligands.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>&#223;-mercaptoethanol</td>
			<td>Fisher</td>
			<td>AC125470100</td>
			<td></td>
		</tr>
		<tr>
			<td>Bromophenol Blue</td>
			<td>Fisher</td>
			<td>B392-5</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium Chloride</td>
			<td>Fisher</td>
			<td>C79-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium Nitrate</td>
			<td>Fisher</td>
			<td>C109-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Disposable Pellet Pestle/Tissue Grinder</td>
			<td>Fisher</td>
			<td>12-141-364</td>
			<td></td>
		</tr>
		<tr>
			<td>Dumont #5 forceps</td>
			<td>Fine Science tools</td>
			<td>11251-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>Atlanta Biologicals</td>
			<td>S11150H</td>
			<td></td>
		</tr>
		<tr>
			<td>Ficoll 400</td>
			<td>Sigma Aldrich</td>
			<td>F9378-500G</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass capillary, 1 X 90 mm</td>
			<td>Narshige</td>
			<td>G-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycerol</td>
			<td>Fisher</td>
			<td>G33-4</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>Fisher</td>
			<td>BP310-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Human chorionic gonadotropin</td>
			<td>Sigma Aldrich</td>
			<td>CG10-10VL</td>
			<td></td>
		</tr>
		<tr>
			<td>Injection Syringe, 1 mL</td>
			<td>Fisher</td>
			<td>8881501368</td>
			<td></td>
		</tr>
		<tr>
			<td>L-Cysteine</td>
			<td>Sigma Aldrich</td>
			<td>C7352</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium Sulfate</td>
			<td>Fisher</td>
			<td>M63-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Needle, 26 G</td>
			<td>Fisher</td>
			<td>305111</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin/Streptomycin</td>
			<td>Gibco</td>
			<td>15140148</td>
			<td></td>
		</tr>
		<tr>
			<td>Picoliter Microinjector</td>
			<td>Warner Instruments</td>
			<td>PLI-100A</td>
			<td></td>
		</tr>
		<tr>
			<td>Pipette Puller</td>
			<td>Narashige</td>
			<td>PC-100</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium Chloride</td>
			<td>Fisher</td>
			<td>P217-500</td>
			<td></td>
		</tr>
		<tr>
			<td>PVDF Membrane</td>
			<td>Sigma Aldrich</td>
			<td>IPVH00010</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Bicarbonate</td>
			<td>Fisher</td>
			<td>S233-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Chloride</td>
			<td>Fisher</td>
			<td>S271-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Dodecyl Sulfate</td>
			<td>Fisher</td>
			<td>BP166-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Hydroxide</td>
			<td>Fisher</td>
			<td>S318-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Tricaine-S</td>
			<td>Pentair</td>
			<td>TRS5</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris</td>
			<td>Fisher</td>
			<td>BP152-5</td>
			<td></td>
		</tr>
	</tbody>
</table>

analysis of transforming growth factor &#223; family cleavage products secreted into the blastocoele of xenopus laevis embryos

The two arms of the Transforming Growth Factor &#223; (Tgf&#223;) superfamily, represented by Tgf&#223;/Nodal or Bone morphogenetic protein (Bmp) ligands, respectively, play essential roles in embryonic development and adult homeostasis. Members of the Tgf&#223; family are made as inactive precursors that dimerize and fold within the endoplasmic reticulum. The precursor is subsequently cleaved into ligand and prodomain fragments. Although only the dimeric ligand can engage Tgf&#223; receptors and activate downstream signaling, there is growing recognition that the prodomain moiety contributes to ligand activity. This article describes a protocol that can be used to identify cleavage products generated during activation of Tgf&#223; precursor proteins. RNA encoding Tgf&#223; precursors are first microinjected into X. laevis embryos. The following day, cleavage products are collected from the blastocoele of&#160;gastrula stage embryos and analyzed on Western blots. This protocol can be completed relatively quickly, does not require expensive reagents and provides a source of concentrated Tgf&#223; cleavage products under physiologic conditions.

The experiment&#39;s goal described below was to determine whether Bmp4 and Bmp7 form heterodimers (dimers composed of one Bmp4 ligand and one Bmp7 ligand), homodimers (composed of two Bmp4 or two Bmp7 ligands), or a mixture of each when they are co-expressed in X. laevis. Data shown in Figure 2 are extracted from a previously published study10. Figure 2A is a schematic showing cleavage products generated by proteolytic maturatio...

Watch this Scientific Journal Video about Analysis of Transforming Growth Factor ÃŸ Family Cleavage Products Secreted Into the Blastocoele of Xenopus laevis Embryos at JoVE.com

Analysis of Transforming Growth Factor &#223; Family Cleavage Products Secreted Into the Blastocoele of Xenopus laevis Embryos

When Transforming Growth Factor &#223; family precursor proteins are ectopically expressed in Xenopus laevis embryos, they dimerize, get cleaved and are secreted into the blastocoele, which begins at the late blastula to early gastrula stage. We describe a method for aspirating cleavage products from the blastocoele cavity for immunoblot analysis.

Analysis of Transforming Growth Factor &#223; Family Cleavage Products Secreted Into the Blastocoele of Xenopus laevis Embryos

The two arms of the Transforming Growth Factor &#223; (Tgf&#223;) superfamily, represented by Tgf&#223;/Nodal or Bone morphogenetic protein (Bmp) ligands, ...

This protocol can be used to study the process by which a wider range of segregated precursor proteins, including TGF-beta family members, are converted to active proteins following proteolytic cleavage. The main advantage of this protocol is that it provides very rapid and inexpensive methods to obtain highly concentrated TGF-beta cleavage product in vivo under visualized condition. To begin with, after the injection on the following day, remove Ficoll solution and any dead or dying embryos, then rinse the embryos once or twice with MBS and culture the embryos in MBS on the bench at room temperature or at 16 degrees Celsius in the incubator to slow down the development.Heat and pull the glass capillaries to a fine point using a micropipette puller with the desired settings. Using forceps, clip off the tip of a pulled needle. To prevent clogging, the opening of the blastocele aspiration needle should be larger than the microinjection needle.Insert the aspiration needle into the needle holder connected to the microinjector and attach the needle holder to the micromanipulator. Place early to mid gastrula stage embryos in an MBS-filled injection tray or dish. Insert the needle below the embryo surface near the animal pole.Press the fill button on the microinjector while observing the needle and the embryo through a dissecting microscope. Over a few seconds, the level of clear fluid rises in the needle and the embryo collapses and becomes concave. Pulse the inject button one or more times to eject any cloudy white matter entering the needle containing debris or proteases.To detect the cleavage products on immunoblots, aspirate the blastocele fluid of 10 to 20 embryos or more depending on antibody. Pipette one microliter of nucleus-free water onto a paraffin piece placed on the injection tray. Submerge the needle in the water drop and press the inject button to dispel the blastocele fluid into the water.Alternatively, to eject the fluid directly onto the parafilm and prevent it from flattening out, pulse the inject button to expel the fluid under lower pressure. Transfer the harvested blastocele fluid into a sterile microcentrifuge tube on ice and add nucleus-free water to adjust the final volume to 30 microliters. To detect TGF-beta precursor proteins, transfer the blastocele fluid depleted embryos to a separate tube on ice.Remove excess MBS and add 200 microliters of pre-chilled embryo lysate buffer. To fully homogenize the embryos, pipette up and down 10 to 20 times until no clumps remain. Centrifuge the homogenized embryos in a refrigerated microcentrifuge at 10, 000 times G for 10 minutes, then remove 160 microliters of the supernatant using a P200 pipette and transfer to a new tube on ice, being careful to avoid the white yolk proteins and other cellular debris in the bottom half of the tube.Repeat the microcentrifugation once and transfer 128 microliters of the clear supernatant to a new tube on ice. At this point, cleared embryo lysates and the blastocele fluid collected can be stored at minus 80 degrees Celsius for as long as desired. Deglycosylate the cleaved proteins present in blastocele fluid modified through the trans-Golgi network with PNGase F by following the manufacturer's instructions.The deglycosylated products would migrate as a more condensed band on SDS gels, which can aid in accurate identification. To assess the prodomain fragment monomers and unfolded proteins in the blastocele and lysate, analyze the proteins under reducing conditions by adding five microliters of reducing 4X sample buffer to 15 microliters blastocele fluid and 15 microliters of clarified embryo lysate. To assess the formation of cleaved homodimeric or heterodimeric ligands in the blastocele, analyze the proteins under non-reducing conditions by adding five microliters of non-reducing 4X sample buffer to the remaining 15 microliters of blastocele fluid, then heat it for five minutes and place it on ice.After using this protocol, the proteins were separated by SDS-PAGE and the immunoblots were probed with antibodies that recognized the myc epitope tag. Under the reducing conditions, in the lysates from embryos expressing only Bmp4 or Bmp7, a single band corresponding to cleaved Bmp4 monomers and a slower migrating band corresponding to cleaved Bmp7 monomers were detected. Both bands were detected in embryos co-expressing Bmp4 and Bmp7.When the proteins were separated under non-reducing conditions, a single mature Bmp4 and 7 heterodimer band of intermediate mobility were detected along with a trace amount of Bmp4 homodimer in the embryos co-expressing Bmp4 and Bmp7. Bmp4 and Bmp7 heterodimer formation was also observed when Bmp7 protein levels were high. However, in this case, the excess Bmp7 formed homodimers and embryos co-expressed Bmp4 and Bmp7.These results demonstrated that Bmp4 and 7 preferentially form heterodimers when co-expressed in Xenopus laevis embryos. In this experiment, collecting pure blastocele is the most important step which requires precise needle handling experience. So just keep trying and fixing errors.This procedure tests whether BMP heterodimers form and which amino acids are important for this. Next step, knockin mouse can be generated to ask whether these amino acids are functionally important during mammalian development.

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Research

JoVE Journal

Developmental Biology

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 ...

Genome-wide Snapshot of Chromatin Regulators and States in Xenopus Embryos by ChIP-Seq

The recruitment of chromatin regulators and the assignment of chromatin states to specific genomic loci are pivotal to cell fate decisions and tissue and organ formation during development. Determining the locations and levels of such chromatin features in vivo will provide valuable information about the spatio-temporal regulation of genomic elements, and will support aspirations to mimic embryonic tissue development in vitro. The most commonly used method for genome-wide and high-resolution profiling is chromatin immunoprecipitation followed by next-generation sequencing (ChIP-Seq). This protocol outlines how yolk-rich embryos such as those of the frog Xenopus can be processed for ChIP-Seq experiments, and it offers simple command lines for post-sequencing analysis. Because of the high efficiency with which the protocol extracts nuclei from formaldehyde-fixed tissue, the method allows easy upscaling to obtain enough ChIP material for genome-wide profiling. Our protocol has been used successfully to map various DNA-binding proteins such as transcription factors, signaling mediators, components of the transcription machinery, chromatin modifiers and post-translational histone modifications, and for this to be done at various stages of embryogenesis. Lastly, this protocol should be widely applicable to other model and non-model organisms as more and more genome assemblies become available.

Genome-wide Snapshot of Chromatin Regulators and States in Xenopus Embryos by ChIP-Seq

The question of how chromatin regulators and chromatin states affect the genome in vivo is key to our understanding of how early cell fate decisions are made in the developing embryo. ChIP-Seq&#8212;the most popular approach to investigate chromatin features at a global level&#8212;is outlined here for Xenopus embryos.

The recruitment of chromatin regulators and the assignment of chromatin states to specific genomic loci are pivotal to cell fate decisions and tissue and ...

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 ...

Methods for Precisely Localized Transfer of Cells or DNA into Early Postimplantation Mouse Embryos

Manipulation and culture of early mouse embryos is a powerful yet largely under-utilized technology enhancing the value of this model system. Conversely, cell culture has been widely used in developmental biology studies. However, it is important to determine whether in vitro cultured cells truly represent in vivo cell types. Grafting cells into embryos, followed by an assessment of their contribution during development is a useful method to determine the potential of in vitro cultured cells. In this study, we describe a method for grafting cells into a defined site of early postimplantation mouse embryos, followed by ex vivo culture. We also introduce an optimized electroporation method that uses glass capillaries of known diameter, allowing precise localization and adjustment of the number of cells receiving exogenous DNA with both high transfection efficiency and low cell death. These techniques, which do not require any specialized equipment, render experimental manipulations of the gastrulation and early organogenesis-stage mouse embryo possible, allowing analysis of commitment in cultured cell subpopulations and the effect of genetic manipulations in situ on cell differentiation.

We demonstrate a method for grafting cultured cells into defined sites of early mouse embryos to determine their in vivo potential. We also introduce an optimized electroporation method that uses glass capillaries of known diameter, allowing the precise delivery of exogenous DNA into a few cells in the embryos.

Manipulation and culture of early mouse embryos is a powerful yet largely under-utilized technology enhancing the value of this model system. Conversely, ...

Quantitative Analysis of Protein Expression to Study Lineage Specification in Mouse Preimplantation Embryos

This protocol presents a method to perform quantitative, single-cell in situ analyses of protein expression to study lineage specification in mouse preimplantation embryos. The procedures necessary for embryo collection, immunofluorescence, imaging on a confocal microscope, and image segmentation and analysis are described. This method allows quantitation of the expression of multiple nuclear markers and the spatial (XYZ) coordinates of all cells in the embryo. It takes advantage of MINS, an image segmentation software tool specifically developed for the analysis of confocal images of preimplantation embryos and embryonic stem cell (ESC) colonies. MINS carries out unsupervised nuclear segmentation across the X, Y and Z dimensions, and produces information on cell position in three-dimensional space, as well as nuclear fluorescence levels for all channels with minimal user input. While this protocol has been optimized for the analysis of images of preimplantation stage mouse embryos, it can easily be adapted to the analysis of any other samples exhibiting a good signal-to-noise ratio and where high nuclear density poses a hurdle to image segmentation (e.g., expression analysis of embryonic stem cell (ESC) colonies, differentiating cells in culture, embryos of other species or stages, etc.).

This protocol presents a method to perform quantitative, single-cell in situ analysis of protein expression to study lineage specification in mouse preimplantation embryos. The procedures necessary for collection of blastocysts, whole-mount immunofluorescent detection of proteins, imaging of samples on a confocal microscope, and nuclear segmentation and image analysis are described.

This protocol presents a method to perform quantitative, single-cell in situ analyses of protein expression to study lineage specification in mouse ...

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 ...

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 ...

Quantitative Whole-mount Immunofluorescence Analysis of Cardiac Progenitor Populations in Mouse Embryos

The use of ever-advancing imaging techniques has contributed broadly to our increased understanding of embryonic development. Pre-implantation development and organogenesis are two areas of research that have benefitted greatly from these advances, due to the high quality of data that can be obtained directly from imaging pre-implantation embryos or ex vivo organs. While pre-implantation embryos have yielded data with especially high spatial resolution, later stages have been less amenable to three-dimensional reconstruction. Obtaining high-quality 3D or volumetric data for known embryonic structures in combination with fate mapping or genetic lineage tracing will allow for a more comprehensive analysis of the morphogenetic events taking place during embryogenesis.
This protocol describes a whole-mount immunofluorescence approach that allows for the labeling, visualization, and quantification of progenitor cell populations within the developing cardiac crescent, a key structure formed during heart development. The approach is designed in such a way that both cell- and tissue-level information can be obtained. Using confocal microscopy and image processing, this protocol allows for three-dimensional spatial reconstruction of the cardiac crescent, thereby providing the ability to analyze the localization and organization of specific progenitor populations during this critical phase of heart development. Importantly, the use of reference antibodies allows for successive masking of the cardiac crescent and subsequent quantitative measurements of areas within the crescent. This protocol will not only enable a detailed examination of early heart development, but with adaptations should be applicable to most organ systems in the gastrula to early somite stage mouse embryo.

Here, we describe a protocol for whole mount immunofluorescence and image-based quantitative volumetric analysis of early stage mouse embryos. We present this technique as a powerful approach to qualitatively and quantitatively assess cardiac structures during development, and propose that it may be widely adaptable to other organ systems.

The use of ever-advancing imaging techniques has contributed broadly to our increased understanding of embryonic development. Pre-implantation development ...

Suppression of Pro-fibrotic Signaling Potentiates Factor-mediated Reprogramming of Mouse Embryonic Fibroblasts into Induced Cardiomyocytes

Trans-differentiation of one somatic cell type into another has enormous potential to model and treat human diseases. Previous studies have shown that mouse embryonic, dermal, and cardiac fibroblasts can be reprogrammed into functional induced-cardiomyocyte-like cells (iCMs) through overexpression of cardiogenic transcription factors including GATA4, Hand2, Mef2c, and Tbx5 both in vitro and in vivo. However, these previous studies have shown relatively low efficiency. In order to restore heart function following injury, mechanisms governing cardiac reprogramming must be elucidated to increase efficiency and maturation of iCMs.
We previously demonstrated that inhibition of pro-fibrotic signaling dramatically increases reprogramming efficiency. Here, we detail methods to achieve a reprogramming efficiency of up to 60%. Furthermore, we describe several methods including flow cytometry, immunofluorescent imaging, and calcium imaging to quantify reprogramming efficiency and maturation of reprogrammed fibroblasts. Using the protocol detailed here, mechanistic studies can be undertaken to determine positive and negative regulators of cardiac reprogramming. These studies may identify signaling pathways that can be targeted to promote reprogramming efficiency and maturation, which could lead to novel cell therapies to treat human heart disease.

Here we present a robust method to reprogram primary embryonic fibroblasts into functional cardiomyocytes through overexpression of GATA4, Hand2, Mef2c, Tbx5, miR-1, and miR-133 (GHMT2m) alongside inhibition of TGF-&#946; signaling. Our protocol generates beating cardiomyocytes as early as 7 days post-transduction with up to 60% efficiency.

Trans-differentiation of one somatic cell type into another has enormous potential to model and treat human diseases. Previous studies have shown that ...

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 ...