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 temperature.</li>
	<li>Allow each eye to fix for 10 - 15 min, then transfer to cold 2x PBS on ice for 5 - 10 min. It is best to stagger enucleations and subsequent fixation to ensure the degree of fixation is equal for each eye.</li>
</ol>
2. Dissection of Postnatal Murine Retinas
<ol>
	<li>Transfer eyes into a Petri dish containing 2x PBS using a plastic Pasteur pipette that has been cut to widen the bore and place under a dissecting microscope.</li>
	<li>Remove any fat around the eye using forceps and scissors.</li>
	<li>Pierce the edge of the cornea with sharp scissors and cut around the cornea and iris and discard.</li>
	<li>Insert forceps between retina and sclera and remove the sclera taking care not to tear the retina. The choroid layer can also be removed, but if there is a risk of damage to the retina occurring during this step, the choroid layer can be left on as it should not significantly affect the quality of the immunostaining.</li>
	<li>Remove the lens and the vitreous humour using forceps.</li>
	<li>Remove the hyaloids vessels by gathering them together in the center of the eye with fine forceps then quickly pull away from the center of the retina (alternatively snip at base of hyaloid vessels with fine scissors).</li>
	<li>Rinse the cup shaped retina with PBS in a clean Petri dish.</li>
	<li>Make 4 to 5 radial incisions reaching approximately 2/3 of the radius of the retina using spring scissors to create a 'petal' shape.</li>
	<li>Draw off PBS using a Pasteur pipette to flatten the retina, and then remove any excess PBS with a small piece of absorbent paper.</li>
	<li>Slowly pipette cold (-20 &deg;C) methanol drop by drop onto surface of retina until totally covered and then flood with additional methanol. This will help to fix the retinas and will facilitate permeabilization. The retinas will turn white.</li>
	<li>Transfer to a 2 ml tube using a plastic Pasteur pipette that has been cut to widen the bore.</li>
	<li>Leave retina in cold methanol for at least 20 min before proceeding with immunostaining. Of the antibodies used here, only VE-Cadherin cannot be used successfully on methanol fixed retinas. In this case retinas need to proceed straight to immunostaining after step 9.</li>
	<li>If required, retinas can be stored in methanol at -20 &deg;C for up to several months prior to staining.</li>
</ol>
3. Immuno/isolectin Staining of the Retinal Vasculature
<ol>
	<li>Carefully remove/pour off methanol and gently rinse retinas briefly in PBS (at this stage the retina is still in the same 2 ml tube from step 11 above).</li>
	<li>Remove PBS and cover retinas with 100 &mu;l of Perm/Block solution (PBS + 0.3% Triton + 0.2% BSA) + 5% of appropriate serum (see Table 1) and shake gently for 1 hr.</li>
	<li>Remove Perm/Block and incubate retinas with gentle shaking overnight at 4 &deg;C with 100 &mu;l of selected primary antibodies (see Table 1) and/or IsolectinB4, all prepared by diluting in Perm/Block.</li>
	<li>Remove antibody/isolectin and wash retinas 4 x 10 min in PBS + 0.3% Triton (PBSTX).</li>
	<li>In some cases, e.g. following staining with IsolectinB4-Alexa488 or a directly conjugated primary antibody, a secondary antibody is not required and retinas can be mounted directly (step 7). When an unconjugated primary antibody has been used in step 3, then 100 &mu;l of the appropriate fluorescent secondary antibody (diluted 1/200 in PBSTX) is added and left to incubate overnight at 4 &deg;C or for 4 hr at room temperature.</li>
	<li>Remove secondary antibody and wash retinas 4 x 15 min in 2 ml PBSTX.</li>
	<li>Transfer retinas onto slides using a wide bore plastic Pasteur pipette and remove excess PBSTX with absorbant tissue. Mount retinas by adding 50 &mu;l of Prolong mountant onto a coverslip and gently position over the retina.</li>
	<li>Transfer slides to fridge overnight at 4 &deg;C, ensuring that they are flat and protected from light, to allow the Prolong mountant to set.</li>
	<li>Image retina using a confocal microscope or an epifluorescence microscope.</li>
</ol>

<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. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+assays+of+angiogenesis+for+assessment+of+angiogenic+and+anti-angiogenic+agents.">In vitro assays of angiogenesis for assessment of angiogenic and anti-angiogenic agents.</a> Microvasc. Res. 74 (2-3), 172-183 (2007).</li><li>Lawson, N. D., Weinstein, B. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+imaging+of+embryonic+vascular+development+using+transgenic+zebrafish.">In vivo imaging of embryonic vascular development using transgenic zebrafish.</a> Dev. Biol. 248 (2), 307-318 (2002).</li><li>Fruttiger, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Development+of+the+retinal+vasculature.">Development of the retinal vasculature.</a> Angiogenesis. 10 (2), 77-88 (2007).</li><li>Sawamiphak, S., Ritter, M., Acker-Palmer, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+of+retinal+explant+cultures+to+study+ex+vivo+tip+endothelial+cell+responses.">Preparation of retinal explant cultures to study ex vivo tip endothelial cell responses.</a> Nat. Protoc. 5 (10), 1659-1665 (1038).</li><li>Mahajan, V. B., Skeie, J. M., Assefnia, A. H., Mahajan, M., Tsang, S. 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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ビデオ: Whole Mount Immunofluorescent Staining of the Neonatal Mouse Retina to Investigate Angiogenesis In vivo

Visualization of the Embryonic Nervous System in Whole-mount Drosophila Embryos

The Drosophila embryo is an attractive model system for investigating the cellular and molecular basis of neuronal development. Here we describe the procedure for the visualization of Drosophila embryonic nervous system using antibodies to neuronal proteins. Since the entire embryonic peripheral nervous and central nervous systems are well characterized at the level of individual cells (Dambly-Chaudi&egrave;re et al., 1986; Bodmer et al., 1987; Bodmer et al., 1989), any aberrations to these systems can be easily identified using antibodies to different neuronal proteins. The developing embryos are collected at certain times to ensure that the embryos are in the proper developmental stages for visualization. After collection, the outer layers of the embryo, the chorion membrane and the vitelline envelope that surrounds the embryo, are removed before fixation. Embryos are then incubated with neuronal antibodies and visualized using fluorescently labeled secondary antibodies. Embryos at stages 12-17 are visualized to access the embryonic nervous system. At stage 12 the CNS germ band starts shortening and by stage 15 the definitive pattern of the commissure has been achieved. By stage 17 the CNS contracts and the PNS is fully developed (Campos-Ortega et al. 1985). Thus changes in the pattern of the PNS and CNS can be easily observed during these developmental stages.

Visualization of the Embryonic Nervous System in Whole-mount Drosophila Embryos

We describe the procedure to prepare staged Drosophila embryos for the visualization of the embryonic nervous system during embryogenesis.

The Drosophila embryo is an attractive model system for investigating the cellular and molecular basis of neuronal development. Here we describe the ...

Dissection of a Mouse Eye for a Whole Mount of the Retinal Pigment Epithelium

The retinal pigment epithelium (RPE) lies at the back of the mammalian eye, just under the neural retina, which contains the photoreceptors (rods and cones). The RPE is a monolayer of pigmented cuboidal cells and associates closely with the neural retina just above it. This association makes the RPE of great interest to researchers studying retinal diseases. The RPE is also the site of an in vivo assay of homology-directed DNA repair, the pun assay. The mouse eye is particularly difficult to dissect due to its small size (about 3.5mm in diameter) and its spherical shape. This article demonstrates in detail a procedure for dissection of the eye resulting in a whole mount of the RPE. In this procedure, we show how to work with, rather than against, the spherical structure of the eye. Briefly, the connective tissue, muscle, and optic nerve are removed from the back of the eye. Then, the cornea and lens are removed. Next, strategic cuts are made that result in significant flattening of the remaining tissue. Finally, the neural retina is gently lifted off, revealing an intact RPE, which is still attached to the underlying choroid and sclera. This whole mount can be used to perform the pun assay or for immunohistochemistry or immunofluorescent assessment of the RPE tissue.

A formal demonstration of the dissection of a mouse eye, resulting in a whole mount of the retinal pigment epithelium.

The retinal pigment epithelium (RPE) lies at the back of the mammalian eye, just under the neural retina, which contains the photoreceptors (rods and ...

In vivo Electroporation of Developing Mouse Retina

The functional characterization of genes expressed during mammalian retinal development remains a significant challenge. Gene targeting to generate constitutive or conditional loss of function knockouts remains cost and labor intensive, as well as time consuming. Adding to these challenges, retina expressed genes may have essential roles outside the retina leading to unintended confounds when using a knockout approach. Furthermore, the ability to ectopically express a gene in a gain of function experiment can be extremely valuable when attempting to identify a role in cell fate specification and/or terminal differentiation.
We present a method for the rapid and efficient incorporation of DNA plasmids into the neonatal mouse retina by electroporation. The application of short electrical impulses above a certain field strength results in a transient increase in plasma membrane permeability, facilitating the transfer of material across the membrane 1,2,3,4. Groundbreaking work demonstrated that electroporation could be utilized as a method of gene transfer into mammalian cells by inducing the formation of hydrophilic plasma membrane pores allowing the passage of highly charged DNA through the lipid bilayer 5. Continuous technical development has resulted in the viability of electroporation as a method for in vivo gene transfer in multiple mouse tissues including the retina, the method for which is described herein 6, 7, 8, 9, 10. 
DNA solution is injected into the subretinal space so that DNA is placed between the retinal pigmented epithelium and retina of the neonatal (P0) mouse and electrical pulses are applied using a tweezer electrode. The lateral placement of the eyes in the mouse allows for the easy orientation of the tweezer electrode to the necessary negative pole-DNA-retina-positive pole alignment. Extensive incorporation and expression of transferred genes can be identified by postnatal day 2 (P2). Due to the lack of significant lateral migration of cells in the retina, electroporated and non-electroporated regions are generated. Non-electroporated regions may serve as internal histological controls where appropriate. 
Retinal electroporation can be used to express a gene under a ubiquitous promoter, such as CAG, or to disrupt gene function using shRNA constructs or Cre-recombinase. More targeted expression can be achieved by designing constructs with cell specific gene promoters. Visualization of electroporated cells is achieved using bicistronic constructs expressing GFP or by co-electroporating a GFP expression construct. Furthermore, multiple constructs may be electroporated for the study of combinatorial gene effects or simultaneous gain and loss of function of different genes. Retinal electroporation may also be utilized for the analysis of genomic cis-regulatory elements by generating appropriate expression constructs and deletion mutants. Such experiments can be used to identify cis-regulatory regions sufficient or required for cell specific gene expression 11. Potential experiments are limited only by construct availability.

In vivo Electroporation of Developing Mouse Retina

A method for the incorporation of plasmid DNA into murine retinal cells for the purpose of performing either gain- or loss of function studies in vivo is presented. This method capitalizes on the transient increase in permeability of cell plasma membranes induced by the application of an external electrical field.

The functional characterization of genes expressed during mammalian retinal development remains a significant challenge.  Gene targeting to generate ...

Whole Mount Immunolabeling of Olfactory Receptor Neurons in the Drosophila Antenna

Odorant molecules bind to their target receptors in a precise and coordinated manner. Each receptor recognizes a specific signal and relays this information to the brain. As such, determining how olfactory information is transferred to the brain, modifying both perception and behavior, merits investigation. Interestingly, there is emerging evidence that cellular transduction and transcriptional factors are involved in the diversification of olfactory receptor neuron. Here we provide a robust whole mount immunological labeling method to assay in vivo olfactory receptor neuron organization. Using this method, we identified all olfactory receptor neurons with anti-ELAV antibody, a known pan-neural marker and Or49a-mCD8::GFP, an olfactory receptor neuron specifically expressed in Nba neuron using anti-GFP antibody.

Whole Mount Immunolabeling of Olfactory Receptor Neurons in the Drosophila Antenna

Herein we describe the process of whole mount immunostaining of Drosophila antennae, which enables us to better understand the molecular mechanisms involved in the diversification of olfactory receptor neurons (ORN)s.

Odorant molecules bind to their target receptors in a precise and coordinated manner. Each receptor recognizes a specific signal and relays this ...

Whole-mount Imaging of Mouse Embryo Sensory Axon Projections

The visualization of full-length neuronal projections in embryos is essential to gain an understanding of how mammalian neuronal networks develop. Here we describe a method to label in situ a subset of dorsal root ganglion (DRG) axon projections to assess their phenotypic characteristics using several genetically manipulated mouse lines. The TrkA-positive neurons are nociceptor neurons, dedicated to the transmission of pain signals. We utilize a TrkAtaulacZ mouse line to label the trajectories of all TrkA-positive peripheral axons in the intact mouse embryo. We further breed the TrkAtaulacZ line onto a Bax null background, which essentially abolishes neuronal apoptosis, in order to assess growth-related questions independently of possible effects of genetic manipulations on neuronal survival. Subsequently, genetically modified mice of interest are bred with the TrkAtaulacZ/Bax null line and are then ready for study using the techniques described herein. This presentation includes detailed information on mouse breeding plans, genotyping at the time of dissection, tissue preparation, staining and clearing to allow for visualization of full-length axonal trajectories in whole-mount preparation.

We present here an optimized protocol to genotype, stain and prepare fetal mice for the imaging of peripheral nociceptor axon projections in the whole animal, as an effective method to assess sensory axon growth phenotypes in developing genetically engineered mice.

The visualization of full-length neuronal projections in embryos is essential to gain an understanding of how mammalian neuronal networks develop. Here we ...

Whole Mount Labeling of Cilia in the Main Olfactory System of Mice

The mouse olfactory system comprises 6-10 million olfactory sensory neurons in the epithelium lining the nasal cavity. Olfactory neurons extend a single dendrite to the surface of the epithelium, ending in a structure called dendritic knob. Cilia emanate from this knob into the mucus covering the epithelial surface. The proteins of the olfactory signal transduction cascade are mainly localized in the ciliary membrane, being in direct contact with volatile substances in the environment. For a detailed understanding of olfactory signal transduction, one important aspect is the exact morphological analysis of signaling protein distribution. Using light microscopical approaches in conventional cryosections, protein localization in olfactory cilia is difficult to determine due to the density of ciliary structures. To overcome this problem, we optimized an approach for whole mount labeling of cilia, leading to improved visualization of their morphology and the distribution of signaling proteins. We demonstrate the power of this approach by comparing whole mount and conventional cryosection labeling of Kirrel2. This axon-guidance adhesion molecule is known to localize in a subset of sensory neurons and their axons in an activity-dependent manner. Whole mount cilia labeling revealed an additional and novel picture of the localization of this protein.

Cilia of olfactory sensory neurons contain proteins of the signal transduction cascade, but a detailed spatial analysis of their distribution is difficult in cryosections. We describe here an optimized approach for whole mount labeling and en face visualization of ciliary proteins.

The mouse olfactory system comprises 6-10 million olfactory sensory neurons in the epithelium lining the nasal cavity. Olfactory neurons extend a single ...

Whole Mount Dissection and Immunofluorescence of the Adult Mouse Cochlea

The organ of Corti, housed in the cochlea of the inner ear, contains mechanosensory hair cells and surrounding supporting cells which are organized in a spiral shape and have a tonotopic gradient for sound detection. The mouse cochlea is approximately 6 mm long and often divided into three turns (apex, middle, and base) for analysis. To investigate cell loss, cell division, or mosaic gene expression, the whole mount or surface preparation of the cochlea is useful. This dissection method allows visualization of all cells within the organ of Corti when combined with immunostaining and confocal microscopy to image cells at different planes in the z-axis. Multiple optical cross-sections can also be obtained from these z-stack images. In addition, the whole mount dissection method can be used for scanning electron microscopy, although a different fixation method is needed. Here, we present a method to isolate the organ of Corti as three intact cochlear turns (apex, middle, and base). This method can be used for mice ranging from one week of age through adulthood and differs from the technique used for neonatal samples where calcification of the cochlea is incomplete. A slightly modified version can be used for dissection of the rat cochlea. We also demonstrate a procedure for immunostaining with fluorescently tagged antibodies.

We present a method to isolate the adult organ of Corti as three intact cochlear turns (apex, middle, and base). We also demonstrate a procedure for immunostaining with fluorescently tagged antibodies. Together these techniques allow the study of hair cells, supporting cells, and other cell types found in the cochlea.

The organ of Corti, housed in the cochlea of the inner ear, contains mechanosensory hair cells and surrounding supporting cells which are organized in a ...

Patch Clamp Recording of Starburst Amacrine Cells in a Flat-mount Preparation of Deafferentated Mouse Retina

The mammalian retina is a layered tissue composed of multiple neuronal types. To understand how visual signals are processed within its intricate synaptic network, electrophysiological recordings are frequently used to study connections among individual neurons. We have optimized a flat-mount preparation for patch clamp recording of genetically marked neurons in both GCL (ganglion cell layer) and INL (inner nuclear layer) of mouse retinas. Recording INL neurons in flat-mounts is favored over slices because both vertical and lateral connections are preserved in the former configuration, allowing retinal circuits with large lateral components to be studied. We have used this procedure to compare responses of mirror-partnered neurons in retinas such as the cholinergic starburst amacrine cells (SACs).

This protocol demonstrates how to perform whole-cell patch clamp recording on retinal neurons from a flat-mount preparation.

The mammalian retina is a layered tissue composed of multiple neuronal types. To understand how visual signals are processed within its intricate synaptic ...

A Simple One-step Dissection Protocol for Whole-mount Preparation of Adult Drosophila Brains

There is an increasing interest in using Drosophila to model human brain degenerative diseases, map neuronal circuitries in adult brains, and study the molecular and cellular basis of higher brain functions. A whole-mount preparation of adult brains with well-preserved morphology is critical for such whole brain-based studies, but can be technically challenging and time-consuming. This protocol describes an easy-to-learn, one-step dissection approach of an adult fly head in less than 10 s, while keeping the intact brain attached to the rest of the body to facilitate subsequent processing steps. The procedure helps remove most of the eye and tracheal tissues normally associated with the brain that can interfere with the later imaging step, and also places less demand on the quality of the dissecting forceps. Additionally, we describe a simple method that allows convenient flipping of the mounted brain samples on a coverslip, which is important for imaging both sides of the brains with similar signal intensity and quality. As an example of the protocol, we present an analysis of dopaminergic (DA) neurons in adult brains of WT (w1118) flies. The high efficacy of the dissection method makes it particularly useful for large-scale adult brain-based studies in Drosophila.

A Simple One-step Dissection Protocol for Whole-mount Preparation of Adult Drosophila Brains

The adult Drosophila brain is a valuable system for studying neuronal circuitry, higher brain functions, and complex disorders. An efficient method to dissect whole brain tissue from the small fly head will facilitate brain-based studies. Here we describe a simple, one-step dissection protocol of adult brains with well-preserved morphology.

There is an increasing interest in using Drosophila to model human brain degenerative diseases, map neuronal circuitries in adult brains, and study the ...

Transpupillary Two-Photon In Vivo Imaging of the Mouse Retina

The retina transforms light signals from the environment into electrical signals that are propagated to the brain. Diseases of the retina are prevalent and cause visual impairment and blindness. Understanding how such diseases progress is critical to formulating new treatments. In vivo&#160;microscopy in animal models of disease is a powerful tool for understanding neurodegeneration and has led to important progress towards treatments of conditions ranging from Alzheimer&#39;s disease to stroke. Given that the retina is the only central nervous system structure inherently accessible by optical approaches, it naturally lends itself towards in vivo imaging. However, the native optics of the lens and cornea present some challenges for effective imaging access.
This protocol outlines methods for in vivo two-photon imaging of cellular cohorts and structures in the mouse retina at cellular resolution, applicable for both acute- and chronic-duration imaging experiments. It presents examples of retinal ganglion cell (RGC), amacrine cell, microglial, and vascular imaging using a suite of labeling techniques including adeno-associated virus (AAV) vectors, transgenic mice, and inorganic dyes. Importantly, these techniques extend to all cell types of the retina, and suggested methods for accessing other cellular populations of interest are described. Also detailed are example strategies for manual image postprocessing for display and quantification. These techniques are directly applicable to studies of retinal function in health and disease.

In vivo imaging is a powerful tool for the study of biology in health and disease. This protocol describes transpupillary imaging of the mouse retina with a standard two-photon microscope. It also demonstrates different in vivoimaging methods to fluorescently label multiple cellular cohorts of the retina.

The retina transforms light signals from the environment into electrical signals that are propagated to the brain. Diseases of the retina are prevalent ...