We would like to thank the Histopathological Service for their technical assistance at the Centro Nacional de Investigaciones Cardiovasculares (CNIC). We also thank Dr. Motoharu Seiki for kindly providing Mt4-mmpLacZ mice, and Dr. Alicia G. Arroyo for supporting our project and for her critical reading of the manuscript. We wish to thank Peter Bonney for proofreading this article. This work was supported by Universidad Europea de Madrid by means of a grant (# 2017UEM01) awarded to C.S.C.

All experimental procedures were approved by the Committee on the Ethics of Animal Experiments of the CNIC (Centro Nacional de Investigaciones Cardiovasculares) and the Comunidad Aut&#243;noma de Madrid to ensure minimal animal suffering.
1. Collection of Embryos from Pregnant Mice (from E8.5 to E12.5)
<ol>
	<li>Sacrifice pregnant mice by either cervical dislocation or CO2 inhalation. The day of the first observed vaginal plug was considered embryonic day 0.5 (E0.5).</li>
	<li>Lay...

The authors declare that they have no competing financial interest.

The E. coli LacZ gene has been widely used as a reporter in studies of gene expression patterns because of its high sensitivity and ease of detection. The present protocol describes a classic method for detecting &#946;-gal expression based on an enzymatic reaction that is easy and quick to perform as well as inexpensive. This method can be also applied without major modifications in whole mount embryos, intact organs, cryostat tissue sections or cultured cells.
Accurate application o...

In order to describe specific gene expression patterns, the use of reporter genes as markers has been paramount from Drosophila to mammals. In experiments involving transgenic and knockout animals, the bacterial &#946;-galactosidase gene (LacZ) of Escherichia coli (E. coli) is one of the most widely used1,2,3,4. &#946;-galactosidase (&#946;-gal) catalyzes the hydrolysis of &#946;-galactosides (such as lactose) into its monosaccharides (glucose and galactose)5. Its most commonly used substrate is X-gal (5-bromo-4-chloro-3-indolyl-&#946;-D-galactopyranoside), a glycoside that is hydrolyzed by &#946;-galactosidase giving rise to 5-bromo-4-chloro-3-hydroxyindole and galactose. The first is oxidized into a dimer that, when used combined with potassium ferri-and ferro-cyanide, produces a characteristic insoluble, blue color precipitate (Figure 1)6.
The LacZ gene started to be used as a reporter gene over thirty years ago7,8. Usually, LacZ is inserted downstream of an endogenous promoter in the place of the open reading frame, so it can be used in bacterial and cell culture to visualize cells containing a particular insert, as well as in transgenic animals as a tracer of endogenous gene expression patterns during development9. In this regard, the visualization of &#946;-galactosidase activity has been extensively used in Drosophila to understand the developmental and cellular processes from single cells to whole tissues. Drosophila genetics favor the generation of stable lines in which a modified P-element construct containing the reporter gene LacZ is inserted at random locations in the genome. Thus, when placed under the influence of enhancer elements it may drive its expression in a tissue specific manner, which has allowed the systematic analysis of the expression patterns of many genes during the past two decades10. In addition, the use of transgenic mice to monitor LacZ gene expression also allows detection of gene recombination events by Cre-loxP mediated recombination, and localization of the mutant embryonic stem cell derivatives in chimeric analyses11, which facilitates the control of LacZ expression in specific tissues as well as temporally. Also, in whole embryos, detection of the &#946;-galactosidase activity may produce differential staining patterns at different intensities that can be conveniently observed across different developmental stages to analyze temporal changes in gene expression8,12.
In this article, we present a protocol to visualize gene expression through X-gal staining in the whole mount tissue at early developmental stages of mouse embryos. We present this histochemical method as a highly sensitive and inexpensive technique that favors accurate detection of the labeled cells either in whole mount specimens or at the cellular level after paraffin embedded tissues or embryos. The method allows for the direct visualization of staining in the mouse tissue with the minimum background when compared with other methods13.

<table>
	<tbody>
		<tr>
			<td>REAGENTS</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>2-Propanol</td>
			<td>SIGMA-ALDRICH</td>
			<td>24137-1L-R</td>
			<td></td>
		</tr>
		<tr>
			<td>Agarose</td>
			<td>SCHARLAU</td>
			<td>50004/ LE3Q2014</td>
			<td></td>
		</tr>
		<tr>
			<td>Aqueous mounting medium</td>
			<td>VECTOR LABS</td>
			<td>H-5501</td>
			<td></td>
		</tr>
		<tr>
			<td>Synthetic mounting media</td>
			<td>MERCK</td>
			<td>100579</td>
			<td></td>
		</tr>
		<tr>
			<td>96% Ethanol</td>
			<td>PROLABO</td>
			<td>20824365</td>
			<td></td>
		</tr>
		<tr>
			<td>99.9% Ethanol absolute</td>
			<td>SCHARLAU</td>
			<td>ET00021000</td>
			<td></td>
		</tr>
		<tr>
			<td>50% Glutaraldehyde solution</td>
			<td>SIGMA-ALDRICH</td>
			<td>G6403-100ml</td>
			<td></td>
		</tr>
		<tr>
			<td>85% Glycerol</td>
			<td>MERCK</td>
			<td>104094</td>
			<td></td>
		</tr>
		<tr>
			<td>99.9% Glycerol</td>
			<td>SIGMA-ALDRICH</td>
			<td>G5516</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium chloride hexahydrate</td>
			<td>SIGMA-ALDRICH</td>
			<td>63064</td>
			<td></td>
		</tr>
		<tr>
			<td>Nonionic surfactant (Nonidet P-40)</td>
			<td>SIGMA-ALDRICH</td>
			<td>542334</td>
			<td></td>
		</tr>
		<tr>
			<td>Nuclear Fast Red counterstain</td>
			<td>SIGMA-ALDRICH</td>
			<td>N3020</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraffin pastilles</td>
			<td>MERCK</td>
			<td>111609</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>SIGMA-ALDRICH</td>
			<td>158127-500g</td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphate buffered saline (tablets)</td>
			<td>SIGMA-ALDRICH</td>
			<td>P4417-50TAB</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium ferrocyanate</td>
			<td>MERCK</td>
			<td>1049840500</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium ferrocyanide</td>
			<td>MERCK</td>
			<td>1049731000</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium azide</td>
			<td>SIGMA-ALDRICH</td>
			<td>S8032</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium deoxycholate</td>
			<td>SIGMA-ALDRICH</td>
			<td>30970</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium dihydrogen phosphate monohydrate</td>
			<td>SIGMA-ALDRICH</td>
			<td>106346</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium phosphate dibasic dihydrate</td>
			<td>SIGMA-ALDRICH</td>
			<td>71638</td>
			<td></td>
		</tr>
		<tr>
			<td>Thymol</td>
			<td>SIGMA-ALDRICH</td>
			<td>T0501</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris hydrochloride (Tris HCl)</td>
			<td>SIGMA-ALDRICH</td>
			<td>10812846001 (Roche)</td>
			<td></td>
		</tr>
		<tr>
			<td>X-GAL</td>
			<td>VENN NOVA</td>
			<td>R-0004-1000</td>
			<td></td>
		</tr>
		<tr>
			<td>Xylene</td>
			<td>VWR CHEMICALS</td>
			<td>VWRC28973.363</td>
			<td></td>
		</tr>
		<tr>
			<td>EQUIPMENT</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Disposable plastic cryomolds 15x15x5 mm</td>
			<td>SAKURA</td>
			<td>4566</td>
			<td></td>
		</tr>
		<tr>
			<td>Rotatory Microtome</td>
			<td>Leica</td>
			<td>RM2235</td>
			<td></td>
		</tr>
		<tr>
			<td>Cassettes</td>
			<td>Oxford Trade</td>
			<td>OT-10-9046</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope Cover Glasses 24x60 mm</td>
			<td>VWR</td>
			<td>ECN631-1575</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope slides</td>
			<td>Thermo Scientific, MENZEL-GL&#196;SER</td>
			<td>AGAA000001#12E</td>
			<td></td>
		</tr>
		<tr>
			<td>Adhesion microscope slides</td>
			<td>Thermo Scientific, MENZEL-GL&#196;SER</td>
			<td>J1820AMNZ</td>
			<td></td>
		</tr>
		<tr>
			<td>Flotation Water bath</td>
			<td>Leica</td>
			<td>HI1210</td>
			<td></td>
		</tr>
		<tr>
			<td>Disposable Low Profile Microtome Blades</td>
			<td>Feather</td>
			<td>UDM-R35</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraffin oven</td>
			<td>J.R. SELECTA</td>
			<td>2000205</td>
			<td></td>
		</tr>
		<tr>
			<td>Wax Paraffin dispenser</td>
			<td>J.R. SELECTA</td>
			<td>4000490</td>
			<td></td>
		</tr>
		<tr>
			<td>Stereomicroscope</td>
			<td>Leica</td>
			<td>DM500</td>
			<td></td>
		</tr>
		<tr>
			<td>Polypropylene microcentrifuge tubes 2.0 mL</td>
			<td>SIGMA-ALDRICH</td>
			<td>T2795</td>
			<td></td>
		</tr>
		<tr>
			<td>Polypropylene microcentrifuge tubes 1.5 mL</td>
			<td>SIGMA-ALDRICH</td>
			<td>T9661</td>
			<td></td>
		</tr>
		<tr>
			<td>Orbital shaker</td>
			<td>IKA Labortechnik</td>
			<td>HS250 BASIC</td>
			<td></td>
		</tr>
		<tr>
			<td>Stirring Hot Plate</td>
			<td>Bibby</td>
			<td>HB502</td>
			<td></td>
		</tr>
		<tr>
			<td>Vortex Shaker</td>
			<td>IKA Labortechnik</td>
			<td>MS1</td>
			<td></td>
		</tr>
		<tr>
			<td>Laboratory scale</td>
			<td>GRAM</td>
			<td>FH-2000</td>
			<td></td>
		</tr>
		<tr>
			<td>Precision scale</td>
			<td>Sartorius</td>
			<td>ISO9001</td>
			<td></td>
		</tr>
		<tr>
			<td>pHmeter</td>
			<td>Crison</td>
			<td>Basic 20</td>
			<td></td>
		</tr>
		<tr>
			<td>Optic fiber</td>
			<td>Optech</td>
			<td>PL2000</td>
			<td></td>
		</tr>
	</tbody>
</table>

tracing gene expression through detection of &#946;-galactosidase activity in whole mouse embryos

The Escherichia coli LacZ gene, encoding &#946;-galactosidase, is largely used as a reporter for gene expression and as a tracer in cell lineage studies. The classical histochemical reaction is based on the hydrolysis of the substrate X-gal in combination with ferric and ferrous ions, which produces an insoluble blue precipitate that is easy to visualize. Therefore, &#946;-galactosidase activity serves as a marker for the expression pattern of the gene of interest as the development proceeds. Here we describe the standard protocol for the detection of &#946;-galactosidase activity in early whole mouse embryos and the subsequent method for paraffin sectioning and counterstaining. Additionally, a procedure for clarifying whole embryos is provided to better visualize X-gal staining in deeper regions of the embryo. Consistent results are obtained by performing this procedure, although optimization of reaction conditions is needed to minimize background activity. Limitations in the assay should be also considered, particularly regarding the size of the embryo in whole mount staining. Our protocol provides a sensitive and a reliable method for &#946;-galactosidase detection during the mouse development that can be further applied to the cryostat sections as well as whole organs. Thus, the dynamic gene expression patterns throughout development can be easily analyzed by using this protocol in whole embryos, but also detailed expression at the cellular level can be assessed after paraffin sectioning.

Here we show the results from applying the standard protocol for the &#946;-galactosidase histochemical reaction using X-gal as the substrate in whole mouse embryos (Figure 1 and Figure 2). By using this protocol, we examine Membrane type 4-matrix metalloproteinase (Mt4-mmp) expression at different embryonic developmental stages (E9.5, E11.5, and E12.5) using Mt4-mmp mutant mice that express the LacZ reporter under the control of...

Watch this Scientific Journal Video about Tracing Gene Expression Through Detection of Î²-galactosidase Activity in Whole Mouse Embryos at JoVE.com

Tracing Gene Expression Through Detection of &amp;#946;-galactosidase Activity in Whole Mouse Embryos

Here we describe the standard protocol for the detection of &#946;-galactosidase activity in early whole mouse embryos and the method for paraffin sectioning and counterstaining. This is an easy and quick procedure to monitor gene expression during development that can also be applied to tissue sections, organs or cultured cells.

Tracing Gene Expression Through Detection of &#946;-galactosidase Activity in Whole Mouse Embryos

The Escherichia coli LacZ gene, encoding &#946;-galactosidase, is largely used as a reporter for gene expression and as a tracer in cell lineage studies. ...

This method can have answer key questions in the developmental biology field such as the study of gene expression patterns during embryonic development.The main advantages of this technique are that it is highly sensitive, easy and quick to perform and allows direct visualization of the staining in the whole mount tissue or at higher resolution after paraffin sectioning of the sample.Demonstrating the procedure will be Dr Maria Jose Blanco, Dr Anabel Learte, Dr Emma Munoz and Dr Miguel Marchena.All of them are senior post-doc from my lab.Begin by incubating glutaraldehyde-fixed transgenic embryos expressing galactosidase in freshly prepared X-gal rinse buffer for 10 minutes at room temperature.Use wild type litter-made embryos as negative controls for the enzymatic reaction.Next, replace the rinse buffer with X-gal staining solution at pH 8-9.Protect from light and incubate for 2 hours to overnight at 37

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Developmental Biology

25.6K visualizações.  Universidad Europea de Madrid. This method can have answer key questions in the developmental biology field such as the study of gene expression patterns during embryonic development.The main advantages of this technique are that it is highly sensitive, easy and quick to perform and allows direct visualization of the staining in the whole mount tissue or at higher resolution after paraffin sectioning of the sample.Demonstrating the procedure will be Dr Maria Jose Blanco, Dr Anabel Learte, Dr Emma Munoz and Dr Miguel Marche...