Name: analysis of cardiac chamber development during mouse embryogenesis using whole mount epifluorescence
Uploaded: 2019-04-17T15:00:00
Description: Watch this Scientific Journal Video about Analysis of Cardiac Chamber Development During Mouse Embryogenesis Using Whole Mount Epifluorescence at JoVE.com

This Work was supported by NIH R03 HL140264 (Y.-J. N) and Gilead Sciences Research Scholar Program (Y.-J. N).

All animal procedures were performed with the approval of the Vanderbilt University Medical Center Institutional Animal Care and Use Committee.
1. Mouse embryo collection and dissection
<ol>
	<li>Mate 8-10 week old female MLC-2v-tdTomato+/- mice with 8-10 week old male MLC-2v-tdTomato+/- mice to obtain MLC-2v-tdTomato+/+, MLC-2v-tdTomato+/- and MLC-2v-tdTomato-/- embryos.</li>
	<li>Check the dams for vaginal plugs every morning. Noon on ...

<ol>
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The method described here is relatively simple to examine ventricular chamber development, without performing labor-intensive experiments to label ventricular or cardiac-specific structural genes or proteins. Thus, this method minimizes technical variabilities that were often found in immunostained heart sections.
There are two critical steps for successfully performing this method including precise estimation of the embryonic age of mice and dissection of embryonic hearts. We practically esti...

Chamber formation during heart development is a complex process transitioning through several morphologically distinct embryonic stages1,2. The crescent shape of cardiac progenitor population cells forms a linear heart tube and then undergoes elongation and looping to form the spiral shape of the developing heart. After its septation process, the developing heart is transformed into the four-chambered heart. Interruption of any of these processes results in developmental heart defects. Thus, it is important to understand the molecular mechanisms underlying chamber formation during heart development. Despite numerous previous studies on heart development, our understanding of this complex process remains limited.
In situ hybridization, immunohistochemistry, and beta-galactosidase staining using LacZ reporter mice have been widely used to study chamber formation during mouse heart development by labeling cardiac specific or chamber specific structural genes or proteins (e.g., Nppa, Coup-TFII, Irx4, MLC-2a and MLC-2v)3,4,5,6,7,8,9,10. However, these experiments using mouse embryos require significant time and expertise, because several different experimental steps have to be performed sequentially11. Here, we describe a simple whole mount epifluorescent microscopy method to visualize the developing ventricles using embryos dissected from MLC-2v-tdTomato reporter knock-in mice12. The advantage of this method compared to previously used methods is to avoid complex experimental steps which may often create experimental variations. The main purpose of this protocol is to describe how to dissect mouse embryos and developing hearts and to examine each stage of mouse cardiac chamber development without tedious histochemical experiments. This method can be easily applied to assess heart development using various other transgenic mouse lines labeling early cardiac markers (e.g., Mesp1Cre: Rosa26EYFP13, Isl1Cre: Rosa26EYFP13, Hcn4H2BGFP14, Hcn4Cre: Rosa mT/mG14, Nkx2-5Cre: Rosa mT/mG14, Hcn4-eGFP15, Isl1Cre: Rosa mT/mG14, Nkx2.5Cre: Rosa26tdTomato15, and TgMef2c-AHF-GFP16 mice).

<table border="0" cellpadding="0" cellspacing="0" style="width:647px;" width="647">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">dissecting microscope</td>
			<td style="width:83px;">Leica</td>
			<td style="width:119px;">MZ125</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">DNA ladder (100 bp)</td>
			<td style="width:83px;">Promega</td>
			<td style="width:119px;">G2101</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">epifluorescence dissecting microscope</td>
			<td style="width:83px;">Leica</td>
			<td style="width:119px;">M165 FC</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">GoTaq Green master Mix</td>
			<td style="width:83px;">Promega</td>
			<td style="width:119px;">M712</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:279px;">PCR machine (master cycler)</td>
			<td style="width:83px;">Eppendorf</td>
			<td style="width:119px;">6336000023</td>
			<td></td>
		</tr>
	</tbody>
</table>

analysis of cardiac chamber development during mouse embryogenesis using whole mount epifluorescence

The goal of this protocol is to describe a method for the dissection of mouse embryos and visualization of embryonic mouse ventricular chambers during heart development using ventricular specific fluorescent reporter knock-in mice (MLC-2v-tdTomato mice). Heart development involves a linear heart tube formation, the heart tube looping, and four chamber septation. These complex processes are highly conserved in all vertebrates. The mouse embryonic heart has been widely used for heart developmental studies. However, due to their extremely small size, dissecting mouse embryonic hearts is technically challenging. In addition, visualization of cardiac chamber formation often needs in situ hybridization, beta-galactosidase staining using LacZ reporter mice, or immunostaining of sectioned embryonic hearts. Here, we describe how to dissect mouse embryonic hearts and directly visualize ventricular chamber formation of MLC-2v-tdTomato mice using whole mount epifluorescent microscopy. With this method, it is possible to directly examine heart tube formation and looping, and four chamber formation without further experimental manipulation of mouse embryos. Although the MLC-2v-tdTomato reporter knock-in mouse line is used in this protocol as an example, this protocol can be applied to other heart-specific fluorescent reporter transgenic mouse lines.

During heart development, MLC-2v is considered to be the earliest marker for ventricular chamber specification17. As depicted in Figure 1, we dissected out mouse whole embryos and embryonic hearts from MLC-2v-tdTomato reporter knock-in mice and examined MLC-2v-tdTomato reporter expression during heart development. In MLC-2v-tdTomato reporter knock-in mice, constitutive tdTomato expression in the developing heart is visualized via epifl...

Watch this Scientific Journal Video about Analysis of Cardiac Chamber Development During Mouse Embryogenesis Using Whole Mount Epifluorescence at JoVE.com

Analysis of Cardiac Chamber Development During Mouse Embryogenesis Using Whole Mount Epifluorescence

We present the protocols to examine mouse heart development using whole mount epifluorescent microscopy on mouse embryos dissected from ventricular specific MLC-2v-tdTomato reporter knock-in mice. This method allows us to directly visualize each stage of the ventricular formation during mouse heart development without labor-intensive histochemical methods.

The goal of this protocol is to describe a method for the dissection of mouse embryos and visualization of embryonic mouse ventricular chambers during ...

Using this method we can directly exam heart tube formation, looping, and full chamber formation without further experimental manipulations of the mouse embryo. Although, we use MLC-2v-tdTomato mice as an example, this simple method can be widely used with other fluorescent reporter mouse lines. The main advantage of this protocol is that it is very simple and does not require any complex techniques or equipment.It can be performed at regular lab setting. After mating female with male mice, both MLC-2v-tdTomato 8 to 10 weeks old, check the dams for vaginal plugs every morning. Lay the pregnant dams, euthanized at different days post coitum, in supine position and spray the abdomen with 70%ethanol.Use sharp surgical scissors and forceps to open the abdominal cavity by incision of both the skin and abdominal wall. After locating bilateral uterine horns in the dorsal part of the abdominal cavity, separate the entire uterus using sharp surgical scissors and forceps to carefully cut above the oviducts on both sides. Place the entire dissected uterus in a 10 centimeter petri dish with ice cold PBS.Using sharp surgical scissors and forceps, carefully separate each amniotic sac along the uterine horn. Use tweezers to transfer each embryo into a 35 millimeter culture plate filled with ice cold PBS. Using sharp surgical scissors and forceps, open an amniotic sac and expose each embryo by cutting off the umbilical cord and then trim out extra embryonic tissues as much as possible without damaging the embryos.Under a dissecting microscope with a fiber optic microscope illuminator, cut off the embryo's head and transfer it to a 1.5 milliliter tube with 100 microliters of buffer A for later genotyping to correlate with the results of epifluorescent imaging. Using fine forceps, open the chest of the embryo. With sharp surgical scissors and forceps, remove the heart away from the lungs and vasculature.Use tweezers to transfer the dissected embryonic heart into a 35 millimeter culture plate with PBS. Place the plate with mouse embryonic hearts under an epifluorescent dissecting microscope. Use fine forceps to position the embryonic hearts such that developing ventricles are facing the examiner.Adjust focus using a 0.63x objective in bright-field mode. Take bright-field exposures and capture multiple images. To visualize tdTomato expression, turn off a fiber optic microscope illuminator and set the filter for red fluorescence.Readjust focusing of the image if necessary, adjust brightness and contrast, take red-fluorescent exposures, and capture multiple images. For embryo genotyping, boil previously isolated head samples in buffer A at 100 degrees Celsius for 30 minutes. Centrifuge for two minutes at 11, 360 times G.Transfer 20 microliters of supernatant into a new 1.5 milliliter tube with 20 microliters of buffer B and mix.Use 4.5 microliters of the mixed supernatant as a DNA template and combine it with 0.5 microliters of each of the 10 micromolar-specific forward and reversed primers, 10 microliters of 2x-premixed polymerase and reaction buffer and then add water to a total volume of 20 microliters. Run a PCR as described in the manuscript. Load the completed reaction in 100 base pair DNA ladder on a 1%agarose gel and run at 140 volts in 1x TAE buffer for 25 minutes.Place the completed gel on a UV transilluminator and turn on the UV light to identify the DNA bands. MLC-2v is considered to be the earliest marker for ventricular chamber specification during heart development. In MLC-2v-tdTomato reporter knock-in mice, relatively weak expression of tdTomato in the linear heart tube at E8.0 becomes stronger at E8.5 as shown using whole-mount epiflourescent imaging of the embryos.Using whole-mount epiflourescent imaging of the dissected heart, ventricular chamber formation during mouse heart development can be easily determined. In the dissected heart from a whole mouse embryo at E10.5, MLC-2v-tdTomato reporter expression was shown in the ventricular portion of the heart and not in the inflow tract, the outflow tract, or the future atria. At E12.5 to E13.5, tdTomato reporter is exclusively expressed in the ventricles of the four-chambered heart.The similar ventricular-specific expression pattern was shown in the dissected mouse embryo at E16.5. After whole imaging, genotype of the embryos was determined using two sets of primers for PCR genotyping, confirming homozygous embryos carrying the tdTomato knock-in allele, heterozygous, and the wild-type embryos. This method is pretty straightforward and simple to perform.The critical step is dissecting embryonic hearts. Understanding cardiac anatomy during heart development is necessary to successfully isolate heart from the whole embryo.

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