We would like to thank Dr. Robert Angerer for his careful reading and editing of the manuscript. NIH R15HD088272-01 as well as the Office of Research and Development, and Department of Biological Sciences at Mississippi State University provided support for this project to RCR.

1. High Throughput Morpholino Design Strategy
<ol>
	<li>Identify a gene(s) of interest (e.g. candidate gene approach, cis-regulatory analysis, RNAseq and/or proteomic differential screens).</li>
	<li>Use genomic, transcriptomic, and gene expression data available on frequently updated websites (e.g. SpBase http://www.echinobase.org&#8203;20&#160;and S. purpuratus Genome Search http:///urchin.nidcr.nih.gov/blast/index.html) to determine that&#160;the spatiotemporal expression profile overlaps with the developmental mechanism in question.&#160;If no expression data is available, then generate qPCR primers and/or an antisense in situ probe to assess the gene expression pattern.</li>
	<li>After determining the spatial and temporal expression pattern, obtain the DNA sequence from the genomic web sites.
	<ol>
		<li>For generating translation-blocking morpholino oligonucleotides, obtain sequence of the 5&#39; un-translated region (5&#39; UTR) directly upstream from the initiation codon from expressed sequence tag (EST) databases available on SpBase or S. purpuratus Genome Search websites. If this information is unavailable for the gene of interest, then perform 5&#39; RACE.</li>
		<li>To design a splice-blocking morpholino, search for the genomic sequence including the exons and introns using the scaffold blastn tool in SpBase or S. purpuratus Genome Search tool.</li>
	</ol>
	</li>
	<li>Use the oligonucleotide designing website http://oligodesign.gene-tools.com in order to design the desired 25 base pair morpholino sequence.
	<ol>
		<li>For a translational-blocking morpholino, use the mRNA sequence from 5&#39; to 3&#39; as the source of translational target sequence. Include the 5&#39; UTR sequence (approximately 70 nucleotides upstream of the transcription start site) plus 25 bases of coding region (downstream of the start site) with the start codon marked with parenthesis (ATG).</li>
		<li>For a splice-blocking morpholino, select intron-exon or exon-intron boundary sequence and include 50 bases (25 bases of exon sequence and 25 bases of intron sequence) around the boundary regions. Scan the genome with the morpholino sequence to verify that the sequence is unique.</li>
	</ol>
	</li>
</ol>
2. Microinjection of Morpholino Oligonucleotides
<ol>
	<li>Prepare 3 mM stock solutions of the morpholino oligonucleotides by adding 100 &#181;L of nuclease-free water into the 300 nmol morpholino vial. 
	NOTE: Do not use DEPC treated water for the re-suspension because diethyl pyrocarbonate can damage the morpholino.</li>
	<li>For the first reconstitution spin down the vial containing the stock oligonucleotide solution for 30 s at full speed (14,000 - 16,000 x g), briefly vortex, heat at 65 &#176;C for 5 to 10 min, briefly vortex, and keep the morpholino stock at room temperature for at least 1 h. Morpholino stock solutions are stored from -20 &#176;C to +4 &#176;C.</li>
	<li>Prepare injection solution containing morpholino oligonucleotides at the desired concentration. This solution usually contains 20% glycerol or 125 mM KCl as a carrier and 15% FITC-Dextran (fluorescein isothiocyanate dextran 10,000 MW 2.5 mg/&#956;L stock solution). FITC-Dextran and other fluorescent dextran conjugates are routinely used to identify injected embryos by epifluorescence microscopy. Store injection solutions at -20 &#176;C.</li>
	<li>Heat the morpholino solution at 65 &#176;C in a heat block or water bath for at least 2 - 5 min.</li>
	<li>Briefly spin the morpholino solution for 30 s at full speed (14,000 - 16,000 x g), vortex for 1 min and centrifuge at full speed (14,000 - 16,000 x g) for at least 10 min.</li>
	<li>Load the injection needles with the morpholino solution. For a detailed microinjection protocol please see Stepicheva and Song, 201421 and Cheers and Ettensohn, 200422.</li>
</ol>
3. Fixation and In Situ Protocol at 24 h Post-fertilization (hpf) in S. purpuratus Embryos
NOTE: This protocol is modified from Arenas-Mena et al., 200023 and Sethi et al., 201424.
<ol>
	<li>Fixation
	<ol>
		<li>Add several drops of fixative (see below) to wells containing embryos, mix gently by pipetting, and allow them to settle. Remove the fixative solution, and then mix embryos with two additional 180 &#181;L washes of fixative. 
		NOTE: It is important to thoroughly mix the embryos during the washes by gentle pipetting up and down several times. Failure to do so can lower the signal to noise ratio.</li>
		<li>Leave the embryos to fix in the second fixative wash for 50 min to 1 h at room temperature (RT) in 4% electron microscopy grade paraformaldehyde consisting of 10 mM MOPS pH 7.0, 0.1% Tween-20, and artificial seawater (ASW). Make this solution fresh each time for best results. In addition, for ease and practicality embryos are fixed in 96-well plates.
		<ol>
			<li>For 20 mL fixative use 5 mL 16% paraformaldehyde, 15 mL ASW, 200 &#181;L 1 M MOPS pH 7.0, and 20 &#181;L Tween-20.</li>
		</ol>
		</li>
		<li>Wash 5 times at RT with 180 &#181;L of MOPS wash buffer consisting of 0.1 M MOPS pH 7.0, 0.5 M NaCl and 0.1% Tween-20 for at least 5 min or until embryos drop to the bottom of the well. Again, It is important to thoroughly mix the embryos into the wash buffer by gently pipetting up and down several times. MOPS wash buffer can be used for 2 days if stored at 4 &#176;C.
		<ol>
			<li>For 40 mL MOPS wash buffer use 4 mL 1 M MOPS pH 7.0, 4 mL 5 M NaCl, 32 mL dH2O, and 40 &#181;L Tween-20.</li>
			<li>Fixed embryos can be stored at 4 oC for 2 days. 
			NOTE: If storing fixed embryos longer, then add 0.2% sodium azide in MOPS wash buffer to prevent bacterial growth.</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Pre-hybridization
	<ol>
		<li>Aspirate the MOPS wash buffer and add 180 &#956;L of a 2:1 ratio of MOPS wash buffer to hybridization buffer, mix embryos into the solution by gentle pipetting several times, and incubate for at least 20 min at RT. Hybridization buffer consists of 70% formamide, 0.1 M MOPS pH 7.0, 0.5 M NaCl, 1 mg/mL BSA and 0.1% Tween-20.
		<ol>
			<li>For 40 mL hybridization buffer use 4 mL 1 M MOPS pH 7.0, 4 mL 5 M NaCl, 4 mL dH2O, 0.04 g BSA, and 40 &#181;L Tween-20. Mix well by vortexing, add 28 mL formamide, and vortex again.</li>
		</ol>
		</li>
		<li>Remove the 2:1 ratio of MOPS wash and hybridization buffers and add 180 &#181;L of a 1:2 ratio of MOPS wash buffer to hybridization buffer, mix embryos into the solution, and incubate for at least 20 min at RT.</li>
		<li>Before probe hybridization gently mix embryos into 100 - 150 &#181;L of hybridization buffer. Incubate embryos at 50 &#176;C for at least 1 h. 
		NOTE: Incubating embryos overnight is acceptable. Before incubating, seal the wells with an adhesive sheet in order to prevent evaporation.</li>
	</ol>
	</li>
	<li>Hybridization
	<ol>
		<li>In a separate tube add 0.1 - 0.3 ng/&#181;L of probe and 500 &#181;g/mL yeast tRNA into hybridization buffer, then vortex gently to create probe solution. Yeast tRNA is added to the probe solution to decrease non-specific binding of the anti-sense probe. Preheat this solution to 50 &#176;C, and aspirate hybridization buffer.</li>
		<li>Mix pre-hybridized embryos into 100 &#181;L of the probe solution, seal with an adhesive sheet, and hybridize at 50 &#176;C for 2 to 7 days depending on the probe (the foxq2 probe can be incubated for 2-days). 
		NOTE: Incubation times will vary based off the probe. Some genes expressed at low levels require up to a 7-day incubation. 96-well plates can be placed in a humidity box as insurance against evaporation if the adhesive sheet fails to seal properly.</li>
		<li>Wash 5 times at 50 &#176;C with 180 &#956;L of freshly made MOPS wash buffer for a total of 3 h. Then, wash 3 times (15 min) with 180 &#181;L of MOPS wash buffer at RT. Remember to mix embryos into the wash buffer each time by gently pipetting several times.</li>
	</ol>
	</li>
	<li>Antibody Incubation
	<ol>
		<li>Aspirate the MOPS wash buffer and mix embryos in 180 &#181;L of blocking buffer consisting of 10% Normal Sheep Serum and 5 mg/mL BSA in MOPS wash buffer and incubate for at least 45 min at RT or 4 &#176;C overnight.</li>
		<li>Remove blocking buffer and then mix embryos into blocking buffer containing a 1:1,500 dilution of alkaline phosphatase-conjugated anti-digoxigenin antibody diluted in blocking buffer. Incubate overnight at RT in a sealed plate to avoid evaporation. NOTE: Do not leave antibody on longer than overnight.</li>
		<li>Wash embryos 6 times (5 min or until embryos drop) in MOPS wash buffer at RT. Embryos can be stored overnight at 4 &#176;C.</li>
	</ol>
	</li>
	<li>In situ development
	<ol>
		<li>Wash embryos 3 times (10 min) at RT with freshly made pH 9.5 buffer consisting of 0.1 M Tris pH 9.5, 100 mM NaCl, 50 mM MgCl2, 1 mM Levamisole, and 0.1% Tween-20.
		<ol>
			<li>For 20 mL pH 9.5 buffer use 2 mL 1 M Tris pH 9.5, 400 &#181;L 5M NaCl, 1 mL 1 M MgCl2, 20 &#181;L Tween-20, 16.6 mL dH2O, and 0.0048 g Levamisole.</li>
		</ol>
		</li>
		<li>Incubate embryos at 37 &#176;C in staining buffer protected from light. Staining buffer consists of 10% Dimethyl Formamide, 4.5 &#181;L/mL 4-Nitro blue tetrazolium chloride (NBT), and 3.5 &#181;L/mL 5-Bromo-4-chloro-3-indolyl-phosphate (BCIP) in freshly made pH 9.5 buffer.
		<ol>
			<li>For 1 mL of staining buffer use 100 &#181;L Dimethyl Formamide, 4.5 &#181;L NBT, and 3.5 &#181;L BCIP.</li>
		</ol>
		</li>
		<li>Stop the alkaline phosphatase reaction by washing 3 to 5 times in MOPS wash buffer. The reaction with the foxq2 probe typically takes 30 min to 1 h. Some probes may need overnight incubation at either RT or 4 &#176;C.</li>
		<li>Mix embryos into a solution of 70% MOPS wash and 30% glycerol. The glycerol provides a refractive index necessary for microscopy. Embryos can be stored in this solution for several weeks. Seal the plates with plastic paraffin to prevent evaporation.</li>
	</ol>
	</li>
	<li>Slide preparation and image capturing
	<ol>
		<li>Prepare a slide by arranging three small strips of double-sided tape into a triangle with small gaps between strips onto a slide.</li>
		<li>Transfer the embryos in the 70% MOPS wash and 30% glycerol solution to the center of the triangle and cover with a coverslip.</li>
		<li>Seal the coverslip by applying a layer of nail polish around the edges of the coverslip.</li>
		<li>Capture images using a compound light microscope with a 20X objective and an attached camera.</li>
	</ol>
	</li>
</ol>

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Development. 138, 1447-1458 (2011).</li><li>Yaguchi, J., Takeda, N., Inaba, K., Yaguchi, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cooperative+Wnt-Nodal+Signals+Regulate+the+Patterning+of+Anterior+Neuroectoderm.">Cooperative Wnt-Nodal Signals Regulate the Patterning of Anterior Neuroectoderm.</a> PLoS Genet. 12, e1006001 (2016).</li><li>Duboc, V., Rottinger, E., Besnardeau, L., Lepage, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nodal+and+BMP2/4+signaling+organizes+the+oral-aboral+axis+of+the+sea+urchin+embryo.">Nodal and BMP2/4 signaling organizes the oral-aboral axis of the sea urchin embryo.</a> Dev Cell. 6, 397-410 (2004).</li><li>Bradham, C. 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=Chordin+is+required+for+neural+but+not+axial+development+in+sea+urchin+embryos.">Chordin is required for neural but not axial development in sea urchin embryos.</a> Dev Biol. 328, 221-233 (2009).</li><li>Su, Y. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gene+regulatory+networks+for+ectoderm+specification+in+sea+urchin+embryos.">Gene regulatory networks for ectoderm specification in sea urchin embryos.</a> Biochimica et biophysica acta. 1789, 261-267 (2009).</li><li>Lin, C. Y., Su, Y. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Genome+editing+in+sea+urchin+embryos+by+using+a+CRISPR/Cas9+system.">Genome editing in sea urchin embryos by using a CRISPR/Cas9 system.</a> Dev Biol. 409, 420-428 (2016).</li></ol>

The authors have nothing to disclose.

The methodology presented here is an example that illustrates the power of using embryos with less genomic and morphological complexity than vertebrates to understand the signaling transduction pathways and GRNs governing fundamental developmental mechanisms.. Many labs are using similar assays during early sea urchin development to dissect the signaling pathways involved in other cell fate specification events (e.g. Notch, Hedgehog, TGF- &#946;, and FGF signaling)27,<sup class...

Gene regulatory networks (GRNs) and signal transduction pathways establish the spatial and temporal expression of genes during embryonic development that are used to build the adult animal body plan. Cell-to-cell signal transduction pathways are essential components of these regulatory networks, providing the means by which cells communicate. These cellular interactions establish and refine the expression of regulatory and differentiation genes in and among the various territories during embryogenesis1,2. Interactions among secreted extracellular modulators (ligands, antagonists), receptors, and co-receptors control the activities of signal transduction pathways. An assortment of intracellular molecules transduces these inputs resulting in altered gene expression, division, and/or shape of a cell. While many of the key molecules used at the extracellular and intracellular levels in the major pathways are known, it is an incomplete knowledge due in large part to the complexity of individual signaling pathways. In addition, different signaling pathways often interact with one another either positively or negatively at the extracellular, intracellular, and transcriptional levels3,4,5,6. Importantly, the core components of signal transduction pathways are highly conserved in all metazoan species, and, remarkably, most of the major signaling pathways often perform similar developmental functions in many species when comparing organisms from closely related phyla in particular 7,8,9,10,11.
The study of signaling during development is a daunting task in any organism, and there are several significant challenges to studying signaling pathways in most deuterostome models (vertebrates, invertebrate chordates, hemichordates, and echinoderms): 1) In vertebrates there are large numbers of possible ligand and receptor/co-modulator interactions, intracellular transduction molecules, as well as potential interactions among different signaling pathways due to the complexity of the genome12,13,14; 2) The complex morphology and morphogenetic movements in vertebrates often make it more difficult to interpret functional interactions in and among signal transduction pathways; 3) Analyses in most non-echinoderm invertebrate deuterostome model species are limited by short windows of gravidity with the exception of some tunicate species15,16.
The sea urchin embryo has few of the above-mentioned limitations and offers many unique qualities for performing a detailed analysis of signal transduction pathways in vivo. These include the following: 1) The relative simplicity of the sea urchin genome significantly reduces the number of possible ligand, receptor/co-receptor and intracellular transduction molecule interactions17; 2) The GRNs controlling the specification and patterning of the germ layers and major embryonic axes are well established in sea urchin embryos, aiding in the understanding of the regulatory context of the cell/territory receiving the signals18,19; 3) Many signal transduction pathways can be studied between early cleavage and gastrula stages when embryos consist of a single layered epithelium whose morphology is easier to analyze; 4) The molecules involved in signaling pathways in the sea urchins are easily manipulated; 5) Many sea urchins are gravid for 10 to 11 months a year (e.g. Strongylocentrotus purpuratus and Lytechinus variegatus).
Here, we present a method to systematically and efficiently characterize components of the signaling pathways that specify and pattern territories in sea urchin embryos to illustrate the advantages that several invertebrate model systems offer in the study of complex molecular mechanisms.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
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		<tr>
			<td>Translational-blocking morpholino and/or splice-blocking morpholino</td>
			<td>Gene Tools LLC</td>
			<td>Customized</td>
			<td>More information at www.gene-tools.com</td>
		</tr>
		<tr>
			<td>Glycerol</td>
			<td>Invitrogen</td>
			<td>15514-011</td>
			<td></td>
		</tr>
		<tr>
			<td>FITC (dextran fluorescein isothiocyanate)</td>
			<td>Invitrogen, Life Technologies</td>
			<td>D1821</td>
			<td>Make 25mg/mL stock solution</td>
		</tr>
		<tr>
			<td>Paraformaldehyde 16% solution EM Grade</td>
			<td>Electron Microscopy Sciences</td>
			<td>15710</td>
			<td></td>
		</tr>
		<tr>
			<td>MOPS</td>
			<td>Sigma Aldrich</td>
			<td>M1254-250G</td>
			<td></td>
		</tr>
		<tr>
			<td>Tween-20</td>
			<td>Sigma Aldrich</td>
			<td>23336-0010</td>
			<td></td>
		</tr>
		<tr>
			<td>Formamide</td>
			<td>Sigma Aldrich</td>
			<td>47671-1L-F</td>
			<td></td>
		</tr>
		<tr>
			<td>Yeast tRNA</td>
			<td>Invitrogen</td>
			<td>15401-029</td>
			<td></td>
		</tr>
		<tr>
			<td>Normal Goat Serum</td>
			<td>Sigma Aldrich</td>
			<td>G9023-10mL</td>
			<td></td>
		</tr>
		<tr>
			<td>Alkaline Phosphatase-conjugated anti-digoxigenin antibody</td>
			<td>Roche</td>
			<td>11 093 274 910</td>
			<td></td>
		</tr>
		<tr>
			<td>Tetramisole hydrochloride (levamisole)</td>
			<td>Sigma Aldrich</td>
			<td>L9756-5G</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris Base UltraPure</td>
			<td>Research Products Internationall Corp</td>
			<td>56-40-6</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Chloride</td>
			<td>Fisher Scientific</td>
			<td>BP358-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium chloride</td>
			<td>Sigma Aldrich</td>
			<td>7786-30-3</td>
			<td></td>
		</tr>
		<tr>
			<td>BCIP (5-Bromo-4-Chloro-3-indolyl-phosphate</td>
			<td>Roche</td>
			<td>11 383 221 001</td>
			<td></td>
		</tr>
		<tr>
			<td>4 Nitro blue tetrazolium chloride (NBT)</td>
			<td>Roche</td>
			<td>11 383 213 001</td>
			<td></td>
		</tr>
		<tr>
			<td>Dimethyl Formamide</td>
			<td>Sigma Aldrich</td>
			<td>D4551-500mL</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium Chloride</td>
			<td>Sigma Aldrich</td>
			<td>P9541-5KG</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Bicarbonate</td>
			<td>Sigma Aldrich</td>
			<td>S5761-500G</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium Sulfate</td>
			<td>Sigma Aldrich</td>
			<td>M7506-2KG</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium Chloride</td>
			<td>Sigma Aldrich</td>
			<td>C1016-500G</td>
			<td></td>
		</tr>
	</tbody>
</table>

the power of simplicity: sea urchin embryos as in vivo developmental models for studying complex cell-to-cell signaling network interactions

Remarkably few cell-to-cell signal transduction pathways are necessary during embryonic development to generate the large variety of cell types and tissues in the adult body form. Yet, each year more components of individual signaling pathways are discovered, and studies indicate that depending on the context there is significant cross-talk among most of these pathways. This complexity makes studying cell-to-cell signaling in any in vivo developmental model system a difficult task. In addition, efficient functional analyses are required to characterize molecules associated with signaling pathways identified from the large data sets generated by next generation differential screens. Here, we illustrate a straightforward method to efficiently identify components of signal transduction pathways governing cell fate and axis specification in sea urchin embryos. The genomic and morphological simplicity of embryos similar to those of the sea urchin make them powerful in vivo developmental models for understanding complex signaling interactions. The methodology described here can be used as a template for identifying novel signal transduction molecules in individual pathways as well as the interactions among the molecules in the various pathways in many other organisms.

In the sea urchin embryo we have shown that 3 different Wnt signaling branches (Wnt/&#946;-catenin, Wnt/JNK, and Wnt/PKC)4,25 interact to form a Wnt signaling network that governs anterior-posterior (AP) patterning. One of the most important consequences of these signaling events is that the initial broadly expressed anterior neuroectoderm (ANE) GRN becomes restricted to a small territory around the anterior pole by the beginning ...

Watch this Scientific Journal Video about The Power of Simplicity: Sea Urchin Embryos as in Vivo Developmental Models for Studying Complex Cell-to-cell Signaling Network Interactions at JoVE.com

The Power of Simplicity: Sea Urchin Embryos as in Vivo Developmental Models for Studying Complex Cell-to-cell Signaling Network Interactions

This video article details a straightforward in vivo methodology that can be used to systematically and efficiently characterize components of complex signaling pathways and regulatory networks in many invertebrate embryos.

The Power of Simplicity: Sea Urchin Embryos as in Vivo Developmental Models for Studying Complex Cell-to-cell Signaling Network Interactions

Remarkably few cell-to-cell signal transduction pathways are necessary during embryonic development to generate the large variety of cell types and ...

The overall goal of these experiments is to illustrate the advantages that simple organisms offer in the study of complex interactions among gene regulatory networks that direct developmental processes.This methodology can help answer key questions in evolutionary and developmental biology, such as how signaling pathways govern cell fate specification along the major embryonic axes in metazoans.One of the main advantages of this methodology is it can be used to efficiently characterize the signaling pathways and the gene regulatory networks that they activate in an in vivo developmental context.Demonstrating this procedure will be Marina Martinez-Bartolom

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7.8K Views.  Mississippi State University. The overall goal of these experiments is to illustrate the advantages that simple organisms offer in the study of complex interactions among gene regulatory networks that direct developmental processes.This methodology can help answer key questions in evolutionary and developmental biology, such as how signaling pathways govern cell fate specification along the major embryonic axes in metazoans.One of the main advantages of this methodology is it can be used to efficiently characterize the si...

Video: The Power of Simplicity: Sea Urchin Embryos as in Vivo Developmental Models for Studying Complex Cell-to-cell Signaling Network Interactions

Protocols for Obtaining Zygotic and Somatic Embryos for Studying the Regulation of Early Embryo Development in the Model Legume Medicago truncatula

Early embryogenesis starting from a single cell zygote goes through rapid cell division and morphogenesis, and is morphologically characterized by pre-globular, globular, heart, torpedo and cotyledon stages. This progressive development is under the tight regulation of a complex molecular network. Harvesting sufficient early embryos at a similar stage of development is essential for investigating the cellular and molecular regulation of early embryogenesis. This is not straightforward since early embryogenesis undergoes rapid morphogenesis in a short while e.g. 8 days for Medicago truncatula to reach the early cotyledon stage. Here, we address the issue by two approaches. The first one establishes a linkage between embryo development and pod morphology in helping indicate the stage of the zygotic embryo. This is particularly based on the number of pod spirals and development of the spines. An alternative way to complement the in vivo studies is via culturing leaf explants to produce somatic embryos. The medium includes an unusual hormone combination - an auxin (1-naphthaleneacetic acid), a cytokinin (6-benzylaminopurine), abscisic acid and gibberellic acid. The different stages can be discerned growing out of the callus without dissection.

Protocols for Obtaining Zygotic and Somatic Embryos for Studying the Regulation of Early Embryo Development in the Model Legume Medicago truncatula

The goal is to illustrate that the model legume Medicago truncatula can be readily utilized to investigate the regulation of early plant embryogenesis to complement the non-legume Arabidopsis model. Pod morphology is linked to zygotic embryogenesis stages and a protocol to collect embryos using tissue culture is also provided.

Early embryogenesis starting from a single cell zygote goes through rapid cell division and morphogenesis, and is morphologically characterized by ...

Characterization of Thymic Settling Progenitors in the Mouse Embryo Using In Vivo and In Vitro Assays

Characterizing thymic settling progenitors is important to understand the pre-thymic stages of T cell development, essential to devise strategies for T cell replacement in lymphopenic patients. We studied thymic settling progenitors from murine embryonic day 13 and 18 thymi by two complementary in vitro and in vivo techniques, both based on the &#8220;hanging drop&#8221; method. This method allowed colonizing irradiated fetal thymic lobes with E13 and/or E18 thymic progenitors distinguished by CD45 allotypic markers and thus following their progeny. Colonization with mixed populations allows analyzing cell autonomous differences in biologic properties of the progenitors while colonization with either population removes possible competitive selective pressures. The colonized thymic lobes can also be grafted in immunodeficient male recipient mice allowing the analysis of the mature T cell progeny in vivo, such as population dynamics of the peripheral immune system and colonization of different tissues and organs. Fetal thymic organ cultures revealed that E13 progenitors developed rapidly into all mature CD3+ cells and gave rise to the canonical &#947;&#948; T cell subset, known as dendritic epithelial T cells. In comparison, E18 progenitors have a delayed differentiation and were unable to generate dendritic epithelial T cells. The monitoring of peripheral blood of thymus-grafted CD3-/- mice further showed that E18 thymic settling progenitors generate, with time, larger numbers of mature T cells than their E13 counterparts, a feature that could not be appreciated in the short term fetal thymic organ cultures.

Characterization of Thymic Settling Progenitors in the Mouse Embryo Using In Vivo and In Vitro Assays

This article describes in vivo and in vitro methodology to characterize the thymic settling progenitors by the analysis of the kinetics of generation, phenotype and numbers of their T cell progeny.

Characterizing thymic settling progenitors is important to understand the pre-thymic stages of T cell development, essential to devise strategies for T ...

Studying Wnt Signaling During Patterning of Conducting Airways

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

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

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

Inducing Complete Polyp Regeneration from the Aboral Physa of the Starlet Sea Anemone Nematostella vectensis

Cnidarians, and specifically Hydra, were the first animals shown to regenerate damaged or severed structures, and indeed such studies arguably launched modern biological inquiry through the work of Trembley more than 250 years ago. Presently the study of regeneration has seen a resurgence using both &#34;classic&#34; regenerative organisms, such as the Hydra, planaria and Urodeles, as well as a widening spectrum of species spanning the range of metazoa, from sponges through mammals. Besides its intrinsic interest as a biological phenomenon, understanding how regeneration works in a variety of species will inform us about whether regenerative processes share common features and/or species or context-specific cellular and molecular mechanisms. The starlet sea anemone, Nematostella vectensis, is an emerging model organism for regeneration. Like Hydra, Nematostella is a member of the ancient phylum, cnidaria, but within the class anthozoa, a sister clade to the hydrozoa that is evolutionarily more basal. Thus aspects of regeneration in Nematostella will be interesting to compare and contrast with those of Hydra and other cnidarians. In this article, we present a method to bisect, observe and classify regeneration of the aboral end of the Nematostella adult, which is called the physa. The physa naturally undergoes fission as a means of asexual reproduction, and either natural fission or manual amputation of the physa triggers re-growth and reformation of complex morphologies. Here we have codified these simple morphological changes in a Nematostella Regeneration Staging System (the NRSS). We use the NRSS to test the effects of chloroquine, an inhibitor of lysosomal function that blocks autophagy. The results show that the regeneration of polyp structures, particularly the mesenteries, is abnormal when autophagy is inhibited.

Inducing Complete Polyp Regeneration from the Aboral Physa of the Starlet Sea Anemone Nematostella vectensis

Here we demonstrate how to induce and monitor regeneration in the Starlet Sea Anemone Nematostella vectensis, a model cnidarian anthozoan. We demonstrate how to amputate and categorize regeneration using a morphological staging system, and we use this system to reveal a requirement for autophagy in regenerating polyp structures.

Cnidarians, and specifically Hydra, were the first animals shown to regenerate damaged or severed structures, and indeed such studies arguably launched ...

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

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

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

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

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

Live Imaging of Mouse Secondary Palate Fusion

The fusion of the secondary palatal shelves to form the intact secondary palate is a key process in mammalian development and its disruption can lead to cleft secondary palate, a common congenital anomaly in humans. Secondary palate fusion has been extensively studied leading to several proposed cellular mechanisms that may mediate this process. However, these studies have been mostly performed on fixed embryonic tissues at progressive timepoints during development or in fixed explant cultures analyzed at static timepoints. Static analysis is limited for the analysis of dynamic morphogenetic processes such a palate fusion and what types of dynamic cellular behaviors mediate palatal fusion is incompletely understood. Here we describe a protocol for live imaging of ex vivo secondary palate fusion in mouse embryos. To examine cellular behaviors of palate fusion, epithelial-specific Keratin14-cre was used to label palate epithelial cells in ROSA26-mTmGflox reporter embryos. To visualize filamentous actin, Lifeact-mRFPruby reporter mice were used. Live imaging of secondary palate fusion was performed by dissecting recently-adhered secondary palatal shelves of embryonic day (E) 14.5 stage embryos and culturing in agarose-containing media on a glass bottom dish to enable imaging with an inverted confocal microscope. Using this method, we have detected a variety of novel cellular behaviors during secondary palate fusion. An appreciation of how distinct cell behaviors are coordinated in space and time greatly contributes to our understanding of this dynamic morphogenetic process. This protocol can be applied to mutant mouse lines, or cultures treated with pharmacological inhibitors to further advance understanding of how secondary palate fusion is controlled.

Here, we present a protocol for live imaging of mouse secondary palate fusion using confocal microscopy. This protocol can be used in combination with a variety of fluorescent reporter mouse lines, and with pathway inhibitors for mechanistic insight. This protocol can be adapted for live imaging in other developmental systems.

The fusion of the secondary palatal shelves to form the intact secondary palate is a key process in mammalian development and its disruption can lead to ...

Visualizing the Node and Notochordal Plate In Gastrulating Mouse Embryos Using Scanning Electron Microscopy and Whole Mount Immunofluorescence

The post-implantation mouse embryo undergoes major shape changes after the initiation of gastrulation and morphogenesis. A hallmark of morphogenesis is the formation of the transient organizers, the node and notochordal plate, from cells that have passed through the primitive streak. The proper formation of these signaling centers is essential for the development of the body plan and techniques to visualize them are of high interest to mouse developmental biologists. The node and notochordal plate lie on the ventral surface of gastrulating mouse embryos around embryonic day (E) 7.5 of development. The node is a cup-shaped structure whose cells possess a single slender cilium each. The proper subcellular localization and rotation of the cilia in the node pit determines left-right asymmetry. The notochordal plate cells also possess single cilia albeit shorter than those of the node cells. The notochordal plate forms the notochord which acts as an important signaling organizer for somitogenesis and neural patterning. Because the cells of the node and notochordal plate are transiently present on the surface and possess cilia, they can be visualized using scanning electron microscopy (SEM). Among other techniques used to visualize these structures at the cellular level is whole mount immunofluorescence (WMIF) using the antibodies against the proteins that are highly expressed in the node and notochordal plate. In this report, we describe our optimized protocols to perform SEM and WMIF of the node and notochordal plate in developing mouse embryos to help in the assessment of tissue shape and cellular organization in wild-type and gastrulation mutant embryos.

The node and notochordal plate are transient signaling organizers in developing mouse embryos that can be visualized using several techniques. Here, we describe in detail how to perform two of the techniques to study their structure and morphogenesis: 1) scanning electron microscopy (SEM); and 2) whole mount immunofluorescence (WMIF).

The post-implantation mouse embryo undergoes major shape changes after the initiation of gastrulation and morphogenesis. A hallmark of morphogenesis is ...

A Layered Mounting Method for Extended Time-Lapse Confocal Microscopy of Whole Zebrafish Embryos

Dynamics of development can be followed by confocal time-lapse microscopy of live transgenic zebrafish embryos expressing fluorescence in specific tissues or cells. A difficulty with imaging whole embryo development is that zebrafish embryos grow substantially in length. When mounted as regularly done in 0.3-1% low melt agarose, the agarose imposes growth restriction, leading to distortions in the soft embryo body. Yet, to perform confocal time-lapse microscopy, the embryo must be immobilized. This article describes a layered mounting method for zebrafish embryos that restrict the motility of the embryos while allowing for the unrestricted growth. The mounting is performed in layers of agarose at different concentrations. To demonstrate the usability of this method, whole embryo vascular, neuronal and muscle development was imaged in transgenic fish for 55 consecutive hours. This mounting method can be used for easy, low-cost imaging of whole zebrafish embryos using inverted microscopes without requirements of molds or special equipment.

This article describes a method to mount fragile zebrafish embryos for extended time-lapse confocal microscopy. This low-cost method is easy to perform using regular glass-bottom microscopy dishes for imaging on any inverted microscope. The mounting is performed in layers of agarose at different concentrations.

Dynamics of development can be followed by confocal time-lapse microscopy of live transgenic zebrafish embryos expressing fluorescence in specific tissues ...

Preparation of Small RNA Libraries for Sequencing from Early Mouse Embryos

MicroRNAs (miRNAs) are important for the complex regulation of cell fate decisions and developmental timing. In vivo studies of the contribution of miRNAs during early development are technically challenging due to the limiting cell number. Moreover, many approaches require a miRNA of interest to be defined in assays such as northern blotting, microarray, and qPCR. Therefore, the expression of many miRNAs and their isoforms have not been studied during early development. Here, we demonstrate a protocol for small RNA sequencing of sorted cells from early mouse embryos to enable relatively unbiased profiling of miRNAs in early populations of neural crest cells. We overcome the challenges of low cell input and size selection during library preparation using amplification and gel-based purification. We identify embryonic age as a variable accounting for variation between replicates and stage-matched mouse embryos must be used to accurately profile miRNAs in biological replicates. Our results suggest that this method can be broadly applied to profile the expression of miRNAs from other lineages of cells. In summary, this protocol can be used to study how miRNAs regulate developmental programs in different cell lineages of the early mouse embryo.

We describe a technique for profiling microRNAs in early mouse embryos. This protocol overcomes the challenge of low cell input and small RNA enrichment. This assay can be used to analyze changes in miRNA expression over time in different cell lineages of the early mouse embryo.

MicroRNAs (miRNAs) are important for the complex regulation of cell fate decisions and developmental timing. In vivo studies of the contribution of miRNAs ...

An Optimized O9-1/Hydrogel System for Studying Mechanical Signals in Neural Crest Cells

Neural crest cells (NCCs) are vertebrate embryonic multipotent cells that can migrate and differentiate into a wide array of cell types that give rise to various organs and tissues. Tissue stiffness produces mechanical force, a physical cue that plays a critical role in NCC differentiation; however, the mechanism remains unclear. The method described here provides detailed information for the optimized generation of polyacrylamide hydrogels of varying stiffness, the accurate measurement of such stiffness, and the evaluation of the impact of mechanical signals in O9-1 cells, a NCC line that mimics in vivo NCCs.
Hydrogel stiffness was measured using atomic force microscopy (AFM) and indicated different stiffness levels accordingly. O9-1 NCCs cultured on hydrogels of varying stiffness showed different cell morphology and gene expression of stress fibers, which indicated varying biological effects caused by mechanical signal changes. Moreover, this established that varying the hydrogel stiffness resulted in an efficient in vitro system to manipulate mechanical signaling by altering gel stiffness and analyzing the molecular and genetic regulation in NCCs. O9-1 NCCs can differentiate into a wide range of cell types under the influence of the corresponding differentiation media, and it is convenient to manipulate chemical signals in vitro. Therefore, this in vitro system is a powerful tool to study the role of mechanical signaling in NCCs and its interaction with chemical signals, which will help researchers better understand the molecular and genetic mechanisms of neural crest development and diseases.

Detailed step-by-step protocols are described here for studying mechanical signals in vitro using multipotent O9-1 neural crest cells and polyacrylamide hydrogels of varying stiffness.

Neural crest cells (NCCs) are vertebrate embryonic multipotent cells that can migrate and differentiate into a wide array of cell types that give rise to ...