This work was funded by the Wellcome Trust and the British Heart Foundation.

All steps are performed at room temperature, unless otherwise indicated.
1. Enucleation and Fixation of Postnatal Eyes
<ol>
	<li>Place humanely killed mouse pup on its side, remove the skin covering the eye with scissors.</li>
	<li>Use scissors and forceps to enucleate the eye.</li>
	<li>Place scissors below the enucleated eye, cut the optic nerve and surrounding tissues and lift out the eye. Transfer to a 24-well plate containing 4% paraformaldehyde (PFA) made up in 2x PBS at room temperatu...

<ol>
	<li>Carmeliet, P., Jain, R. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+mechanisms+and+clinical+applications+of+angiogenesis.">Molecular mechanisms and clinical applications of angiogenesis.</a> Nature. 473 (7347), 298-307 (2011).</li><li>Staton, 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=Current+methods+for+assaying+angiogenesis+in+vitro+and+in+vivo.">Current methods for assaying angiogenesis in vitro and in vivo.</a> Int J. Exp. Pathol. 85 (5), 233-248 (2004).</li><li>Goodwin, A. 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H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mouse+eye+enucleation+for+remote+high-throughput+phenotyping.">Mouse eye enucleation for remote high-throughput phenotyping.</a> J. Vis. Exp. (57), e3184 (2011).</li><li>Pitulescu, M. E., Schmidt, I., Benedito, R., Adams, R. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inducible+gene+targeting+in+the+neonatal+vasculature+and+analysis+of+retinal+angiogenesis+in+mice.">Inducible gene targeting in the neonatal vasculature and analysis of retinal angiogenesis in mice.</a> Nat. Protoc. 5 (9), 1518-1534 (2010).</li><li>Allinson, K. R., Lee, H. S., Fruttiger, M., McCarty, J., Arthur, H. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Endothelial+expression+of+TGFbeta+type+II+receptor+is+required+to+maintain+vascular+integrity+during+postnatal+development+of+the+central+nervous+system.">Endothelial expression of TGFbeta type II receptor is required to maintain vascular integrity during postnatal development of the central nervous system.</a> PLoS One. 7 (9), e39336 (2012).</li><li>Mahmoud, M., 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=Pathogenesis+of+arteriovenous+malformations+in+the+absence+of+endoglin.">Pathogenesis of arteriovenous malformations in the absence of endoglin.</a> Circ. Res. 106 (8), 1425-1433 (2010).</li><li>Lebrin, F., 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=Thalidomide+stimulates+vessel+maturation+and+reduces+epistaxis+in+individuals+with+hereditary+hemorrhagic+telangiectasia.">Thalidomide stimulates vessel maturation and reduces epistaxis in individuals with hereditary hemorrhagic telangiectasia.</a> Nat. Med. 16 (4), 420-428 (2010).</li><li>Pi, L., 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=Role+of+connective+tissue+growth+factor+in+the+retinal+vasculature+during+development+and+ischemia.">Role of connective tissue growth factor in the retinal vasculature during development and ischemia.</a> Invest. Ophthalmol. Vis. Sci. 52 (12), 8701-8710 (2011).</li><li>Powner, M. 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=Visualization+of+gene+expression+in+whole+mouse+retina+by+in+situ+hybridization.">Visualization of gene expression in whole mouse retina by in situ hybridization.</a> Nat. Protoc. 7 (6), 1086-1096 (2012).</li></ol>

The authors declare that they have no competing financial interests.

The method presented here offers a simple and efficient way to obtain images of stained whole mount preparations of neonatal mouse retinas, making it an easily quantifiable and physiologically relevant model of angiogenesis. Initially, the mouse eye can be quite difficult to dissect due to its small size and globe shape, so some practice and good dissection tools are needed for reliable results. Dissection of eyes prepared in 2x concentration of PBS is important because this causes a small amount of water loss from the e...

Angiogenesis is a complex developmental process defined by the formation of new blood vessels from a pre-existing vessel network and is regulated by several signalling pathways. The most prominent of these is the VEGF pathway. VEGF is released by ischemic cells and leads to the initiation of angiogenic sprouting in neighboring blood vessels. The leading endothelial cell from a new vascular sprout is a 'tip' cell, which produces filopodia that reach out towards the source of VEGF, and is followed by proliferating 'stalk' endothelial cells. In this way, activated endothelial cells migrate and proliferate towards an avascular region where they form new vascular tubes. In order to stabilize these tubes to support blood flow, endothelial cells interact with pericytes and smooth muscle cells, which surround the new blood vessels 1. Angiogenesis is essential for vascularization of the embryo and growing tissues. However, it also contributes to many pathological disorders such as cancer; whereas defects in angiogenesis are associated with ischemic diseases. The development of effective drug treatments to regulate angiogenesis as a means of treating disease is therefore of great interest. For example, effective anti-angiogenic factors will reduce cancer growth, whilst pro-angiogenic strategies can be used to treat ischemic disease. Thus, models of angiogenesis are essential to better understand the regulation of new vessel formation and for developing new therapeutic strategies to enhance or decrease vascular growth.
A fundamental element of angiogenesis research is the choice of an appropriate vascular model. Many in vitro models have been designed to reproduce the basic steps of angiogenesis such as endothelial cell migration, proliferation and survival 2,3 . A frequently used in vitro assay is the formation of a branched network of endothelial cells on a Matrigel matrix, although this is not specific for endothelial cells, nor does it usually incorporate the support of pericytes or smooth muscle cells. Assessment of ex vivo sprouting angiogenesis using mouse organ culture such as the embryoid body assay, the aortic ring assay and the fetal metatarsal assay allows the analysis of angiogenesis of endothelial cells in the context of additional supporting cells. However, the main limitations of these assays include the lack of blood flow and the regression of vessels over time, giving a limited window for analysis. Therefore, to understand the regulation of angiogenesis more accurately, in vivo models are required such as those developed in mouse using subcutaneously implanted sponges or matrigel plugs, as well as the hind limb ischemia model. However, these models are challenging to analyze due to the complex 3D architecture of the neovessels. In contrast, the zebrafish embryo has proved an excellent model for visualizing angiogenesis in the whole organism 4. However, the mouse is evolutionarily much more closely related to human than zebrafish, making the mouse a preferred model in many cases. Consequently angiogenesis of the postnatal mouse retina represents a well characterized method of choice for angiogenesis research. It not only provides a physiological setting, but also a 2D vascular plexus that can be readily visualized using appropriate fluorescent stains. The architecture of the vessel network, endothelial proliferation, sprouting, perivascular cell recruitment and vessel remodelling can all be investigated using this technique.
In the neonatal mouse retina, development of retinal blood vessels occurs in the first week of postnatal life. Mice, unlike humans, are born blind and the retinas only become vascularized after birth. Retinal vessels arise from the center of the retina close to the optic nerve at postnatal day 0 (P0), and develop by angiogenesis to form a highly organized vascular plexus that reaches the retinal periphery by approximately P8 5. Blood vessels develop in a characteristic manner with the capillary plexus gradually growing outward from the optic disc toward the periphery to generate a regular alternating pattern of arteries and veins with an intervening capillary network. The retinal vasculature provides an ideal model to study angiogenesis as the vessels can be easily identified as they grow in what is essentially a 2D plane, thus making it relatively easy to examine the retinal vasculature in flat-mount preparations 5. A method for isolating the mouse neonatal retina for analysis of endothelial tip cell responses over several hours ex vivo has been reported 6. Alternatively, a more detailed investigation of the whole retinal vasculature and associated vascular markers requires immunostaining of fixed retina specimens at different stages of development.
Here we provide a detailed description of a reliable and technically straight forward method that we use for whole mount staining of the murine retinal vascular plexus, from the initial enucleation of the postnatal eye (see also 7) through the staining protocols to final imaging under the microscope.

<table border="1">
	<tbody>
		<tr>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>Material</td>
		</tr>
		<tr>
			<td>Plastic pipettes 3 ml</td>
			<td>Scientific Laboratory Supplies</td>
			<td>PIP4210</td>
			<td>Remove tip with scissors to create a wide bore</td>
		</tr>
		<tr>
			<td>BD Falcon 24-well plates</td>
			<td>Scientific Laboratory Supplies</td>
			<td>353226</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Select Petri dishes TV 90 mm</td>
			<td>Scientific Laboratory Supplies</td>
			<td>SLS2002</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Histobond slides</td>
			<td>VWR</td>
			<td>631-0624</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Coverslips 22 x 22 mm</td>
			<td>VWR</td>
			<td>631-1336</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Dumont Tweezers #5</td>
			<td>World precision instruments</td>
			<td>14095</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Spring scissors 10.5 cm long, with straight 8 mm blades</td>
			<td>World precision instruments</td>
			<td>501235</td>
			<td>Used for enucleation</td>
		</tr>
		<tr>
			<td>Vannas scissors 8.5 cm long, with straight 7 mm blades, and 0.025 x 0.015 mm superfine tips</td>
			<td>World precision instruments</td>
			<td>500086</td>
			<td>Used for dissecting retina</td>
		</tr>
		<tr>
			<td>Superfine vannas scissors 8 cm long with straight 3 mm blades, and 0.015 x 0.015 mm superfine tips</td>
			<td>World precision instruments</td>
			<td>501778</td>
			<td>Used for dissecting retina</td>
		</tr>
		<tr>
			<td>crystal clear' tubes 2 ml</td>
			<td>Starlab</td>
			<td>E1420-2000</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>Reagents</td>
		</tr>
		<tr>
			<td>Sodium phosphate dibasic</td>
			<td>Sigma</td>
			<td>S0876</td>
			<td>PBS reagent</td>
		</tr>
		<tr>
			<td>Potassium phosphate monobasic</td>
			<td>Sigma</td>
			<td>P5655</td>
			<td>PBS reagent</td>
		</tr>
		<tr>
			<td>Sodium chloride</td>
			<td>Sigma</td>
			<td>S9625</td>
			<td>PBS reagent</td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>Sigma</td>
			<td>P6148</td>
			<td>Make up in 2x PBS and store at -20 &deg;C</td>
		</tr>
		<tr>
			<td>BSA</td>
			<td>Sigma</td>
			<td>A7638</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Sigma</td>
			<td>T9284</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Donkey serum</td>
			<td>Sigma</td>
			<td>D9663</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Goat serum</td>
			<td>Vector</td>
			<td>S-1000</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Prolong Gold anti-fade reagent</td>
			<td>Invitrogen</td>
			<td>P36930</td>
			<td>Mounting reagent</td>
		</tr>
		<tr>
			<td>Isolectin GS-IB4-alexa 594</td>
			<td>Invitrogen</td>
			<td>I21413</td>
			<td>Use at 1:200 dilution</td>
		</tr>
		<tr>
			<td>Isolectin GS-IB4-alexa 488</td>
			<td>Invitrogen</td>
			<td>I21411</td>
			<td>Use at 1:200 dilution</td>
		</tr>
		<tr>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>Primary Antibodies</td>
		</tr>
		<tr>
			<td>Anti-NG2 (rabbit polyclonal )</td>
			<td>Millipore</td>
			<td>AB5320</td>
			<td>Detects pericytes</td>
		</tr>
		<tr>
			<td>Anti-GFAP (clone GA5, mouse monoclonal)</td>
			<td>Millipore</td>
			<td>MAB360</td>
			<td>Detects astrocytes</td>
		</tr>
		<tr>
			<td>Anti-Desmin (clone Y66, rabbit monoclonal)</td>
			<td>Millipore</td>
			<td>04-585</td>
			<td>Detects pericytes</td>
		</tr>
		<tr>
			<td>Anti-Collagen IV (rabbit polyclonal )</td>
			<td>Chemicon</td>
			<td>AB756P</td>
			<td>Detects vascular basement membrane</td>
		</tr>
		<tr>
			<td>Anti-alpha smooth muscle actin-Cy3 (clone 1A4, mouse monoclonal)</td>
			<td>Sigma</td>
			<td>C6198</td>
			<td>Detects vascular smooth muscle cells.</td>
		</tr>
		<tr>
			<td>Anti-Endoglin (clone MJ7/18, rat monoclonal)</td>
			<td>BD Pharmingen</td>
			<td>550546</td>
			<td>Detects endothelial cells</td>
		</tr>
		<tr>
			<td>Anti-CD31 (clone MEC13.3, rat monoclonal)</td>
			<td>BD Pharmingen</td>
			<td>553370</td>
			<td>Detects endothelial cells</td>
		</tr>
		<tr>
			<td>Anti-VE-Cadherin (clone 11D4.1, rat monoclonal)</td>
			<td>BD Pharmingen</td>
			<td>550548</td>
			<td>Detects endothelial cell junctions</td>
		</tr>
		<tr>
			<td>Anti-Alk1 (goat polyclonal)</td>
			<td>R&amp;D Systems</td>
			<td>AF770</td>
			<td>Detects endothelial cells</td>
		</tr>
		<tr>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>Secondary Antibodies</td>
		</tr>
		<tr>
			<td>Goat anti-rabbit-Alexa594</td>
			<td>Invitrogen</td>
			<td>A11012</td>
			<td>All secondary antibodies are aliquoted immediately on arrival and stored at -20 &deg;C.</td>
		</tr>
		<tr>
			<td>Goat anti-rat-Alexa488</td>
			<td>Invitrogen</td>
			<td>A11006</td>
			<td>All secondary antibodies are aliquoted immediately on arrival and stored at -20 &deg;C.</td>
		</tr>
		<tr>
			<td>Goat anti-rat-Alexa594</td>
			<td>Invitrogen</td>
			<td>A11007</td>
			<td>All secondary antibodies are aliquoted immediately on arrival and stored at -20 &deg;C.</td>
		</tr>
		<tr>
			<td>Goat anti-mouse-Alexa488</td>
			<td>Invitrogen</td>
			<td>A11029</td>
			<td>All secondary antibodies are aliquoted immediately on arrival and stored at -20 &deg;C.</td>
		</tr>
		<tr>
			<td>Donkey anti-goat-Alexa594</td>
			<td>Invitrogen</td>
			<td>A11058</td>
			<td>All secondary antibodies are aliquoted immediately on arrival and stored at -20 &deg;C.</td>
		</tr>
		<tr>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>&nbsp;</td>
			<td>Microscopes</td>
		</tr>
		<tr>
			<td>Dissection microscope</td>
			<td>Zeiss</td>
			<td>Stemi SV6</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Camera</td>
			<td>Zeiss</td>
			<td>Axiocam HRc</td>
			<td>Camera for dissection microscope</td>
		</tr>
		<tr>
			<td>Epifluorescent Microscope</td>
			<td>Zeiss</td>
			<td>Axioimager with Apotome</td>
			<td>&nbsp;</td>
		</tr>
		<tr>
			<td>Camera</td>
			<td>Zeiss</td>
			<td>Axiocam HRm</td>
			<td>Camera for Axioimager</td>
		</tr>
		<tr>
			<td>Confocal Microscope</td>
			<td>Nikon</td>
			<td>A1R</td>
			<td>&nbsp;</td>
		</tr>
	</tbody>
</table>

whole mount immunofluorescent staining of the neonatal mouse retina to investigate angiogenesis in vivo

Angiogenesis is the complex process of new blood vessel formation defined by the sprouting of new blood vessels from a pre-existing vessel network. Angiogenesis plays a key role not only in normal development of organs and tissues, but also in many diseases in which blood vessel formation is dysregulated, such as cancer, blindness and ischemic diseases. In adult life, blood vessels are generally quiescent so angiogenesis is an important target for novel drug development to try and regulate new vessel formation specifically in disease. In order to better understand angiogenesis and to develop appropriate strategies to regulate it, models are required that accurately reflect the different biological steps that are involved. The mouse neonatal retina provides an excellent model of angiogenesis because arteries, veins and capillaries develop to form a vascular plexus during the first week after birth. This model also has the advantage of having a two-dimensional (2D) structure making analysis straightforward compared with the complex 3D anatomy of other vascular networks. By analyzing the retinal vascular plexus at different times after birth, it is possible to observe the various stages of angiogenesis under the microscope. This article demonstrates a straightforward procedure for analyzing the vasculature of a mouse retina using fluorescent staining with isolectin and vascular specific antibodies.

After dissection the retina should look like a flat flower (Figure 1). By using the protocol, outlined above, endothelial cells can be seen using isolectin B4-Alexa488 staining and supporting vascular muscle cells are visualized using anti-alpha smooth muscle actin (Figure 2). The low power view using a 5X objective in Figure 2 allows an overview of the vascular organization of the retina. Also, by using a different combination of antibodies given in the protocol above, ...

Watch this Scientific Journal Video about Whole Mount Immunofluorescent Staining of the Neonatal Mouse Retina to Investigate Angiogenesis In vivo at JoVE.com

Whole Mount Immunofluorescent Staining of the Neonatal Mouse Retina to Investigate Angiogenesis In vivo

The neonatal murine retina provides a well characterized physiological model of angiogenesis, which permits investigations of the roles of different genes or drugs that modulate angiogenesis in an in vivo context. Immunofluorescent staining to accurately visualize the vascular plexus is pivotal to the success of these types of studies.

Whole Mount Immunofluorescent Staining of the Neonatal Mouse Retina to Investigate Angiogenesis In vivo

Angiogenesis  is the complex process of new blood vessel formation defined by the sprouting  of new blood vessels from a pre-existing vessel network. ...

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45.2K Views.  Newcastle University. The neonatal murine retina provides a well characterized physiological model of angiogenesis, which permits investigations of the roles of different genes or drugs that modulate angiogenesis in an in vivo context. Immunofluorescent staining to accurately visualize the vascular plexus is pivotal to the success of these types of studies.