Name: high-throughput analysis of mammalian olfactory receptors: measurement of receptor activation via luciferase activity
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Description: Watch this Scientific Journal Video about High-throughput Analysis of Mammalian Olfactory Receptors: Measurement of Receptor Activation via Luciferase Activity at JoVE.com

This work was supported by R01 DC013339, R03 DC011373, and Ruth L. Kirschstein National Research Service Award T32 DC000014. A portion of the work was performed using the Monell&#160;Chemosensory Receptor Signaling Core, which is supported, in part, by funding from the NIH-NIDCD Core Grant P30 DC011735. The authors thank C. Sezille for help with data collection.

1. Culture of Hana3A Cells
<ol>
	<li>Prepare M10 media by supplementing minimum essential medium (MEM) with 10% (v/v) FBS.</li>
	<li>Culture Maintenance
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		<li>Maintain cells in M10 media. NOTE: The expression vectors for RTP1L, RTP2, REEP1, and G&#945;olf confer puromycin resistance to Hana3A cells, but maintaining the cells with this antibiotic does not significantly affect assay results.</li>
		<li>Subculture at a ratio of 1:8 in 10 cm dishes every 2-3 days.</li>
		<li>Incubate at 37 &#176;C with 5% ...

<ol>
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Odorant identity is encoded by olfactory receptor activation patterns, but receptor activation patterns, including which receptors are activated and to what degree, are known for fewer than 6% of human olfactory receptors1-11. Efforts to characterize olfactory receptors have been limited by their labor-intensive methods or applicability to only a subset of the olfactory receptor family17,23,24,33,34. The Hana3A heterologous expression system supports the robust expression of the majority of tested o...

The mammalian olfactory system has the ability to respond to a vast number of odorous stimuli, allowing for the detection and discrimination of thousands of odorants. Olfactory receptors (ORs) are the molecular sensors expressed by the olfactory sensory neurons in the olfactory epithelium12. Mammalian odor recognition occurs through differential activation of ORs by odorants, and the OR gene family is extensive, with roughly 1,000 murine and 400 human receptors12-16. Previous functional analyses of ORs in olfactory neurons and in heterologous cells have shown that different odorants are recognized by unique, but overlapping ensembles of ORs10,17-20. Matching ligands to ORs is critical for understanding the olfactory code and essential for building viable models of olfaction. Due to difficulties expressing ORs in heterologous systems as well as the large number of both odorants and ORs, this data has been largely absent from the field; indeed, fewer than 6% of human ORs have a published ligand1-11. This protocol describes the use of a luciferase assay to characterize odorant/OR interactions. This assay enables the high-throughput characterization of ORs, a task that is essential to understanding odorant/OR interactions as well as developing a model of odor coding.
High-throughput studies of ORs face three major challenges. First, ORs expressed in heterologous cells were retained in the ER and subsequently degraded in the proteasome21,22, preventing the ORs from interacting with odorants in the assay system23-25. This problem was addressed by the discovery of accessory proteins that facilitate stable cell-surface expression of a broad range of ORs19,26,27. Receptor-transporter-proteins 1 and 2 (RTP1 and 2) promote OR cell-surface expression and activation in response to odorant stimulation19. Based on this work, HEK293T cells were modified to stably express RTP1 long (RTP1L) and RTP2, receptor expression-enhancing protein 1, and G&#945;olf, resulting in the Hana3A cell line19,27. In addition, the type 3 muscarinic acetylcholine receptor (M3-R) interacts with ORs at the cell surface and enhances activation in response to odorants26. Co-transfection of an OR with RTP1S and M3-R into Hana3A cells results in the robust, consistent, and functional expression of a broad range of ORs at the cell surface27. Second, mammalian OR repertoires are quite large. In humans, for example, the OR repertoire is an order of magnitude more numerous than the gustatory receptor repertoire, and 2&#160;orders of magnitude more numerous than the visual receptor repertoire. Although cloning a single OR is a relatively straightforward protocol, significant up-front effort is required to generate a comprehensive library. Third, although we know that in vision, wavelength translates into color and in audition frequency translates into pitch, the organization of odors is poorly understood, making it difficult for researchers to interpolate from a representative sample of odorants. Although some progress has been made on this front10,28, the map of the olfactory landscape remains incomplete. Screening tens of thousands of molecules against hundreds of ORs is a daunting task; high-throughput screens in this domain require carefully defined campaigns. The major remaining challenges are those of logistics and cost rather than problems inherent to the technique. Although heterologous screening has not been widely used to identify ligands by academic groups, a private company has used the same technique to identify ligands for 100 human ORs 29. Unfortunately, these data remain proprietary.
The high-throughput luciferase assay outlined here has several advantages over alternative methods used to assess OR activation. Although the responses of native olfactory sensory neurons have been measured using electrophysiology and calcium imaging, these techniques have difficulty teasing apart which OR leads to a neuron&#39;s response due to the overlap in response properties for olfactory neurons. Although knocking-in a GFP-labeled receptor type30,31, delivering specific receptors via adenovirus to murine olfactory neurons32,33, or performing RT-PCR after recordings17,24,33 can link recordings to single receptor types, these methods are low-throughput and not suitable for large-scale screens. Heterologous screening systems are more scalable, and two major forms are found in the literature: cAMP pathway reporters and inositol triphosphate (IP3) pathway reporters. Upon odor stimulation, ORs activate a G&#945;olf transduction signaling cascade that results in the production of cyclic AMP (cAMP)12. By co-transfecting a firefly luciferase reporter gene under the control of a cAMP response element (CRE), luciferase production can be measured as a function of odor response, allowing for the quantification of OR activation. OR activation can also be linked to the IP3 pathway by co-expressing G-proteins such as G&#945;15/16 or a G&#945;15-olf chimera24,25,34. We have chosen the assay presented here based on three factors: (1) the co-expression of RTP1 with Rho-tagged olfactory receptors improves the expression of olfactory receptors at the cell surface19,27; (2) use of a cAMP-responsive reporter gene allows for the measurement of OR activation through the canonical second messenger pathway; and (3) the assay is well-suited to high-throughput screens.
This high-throughput luciferase assay is applicable to a variety of studies valuable to the field of olfaction. First, a large number of ORs can be screened against a single odorant in order to determine the receptor activation pattern for a specific odorant. This type of study identified OR7D4 as the OR responsible for responding to the steroid odorant androstenone8. Conversely, one OR can be screened against a panel of odorants in order to determine the receptor response profile10. When candidate olfactory odorant/OR pairs are identified via these screens, interaction can be confirmed by conducting a dose response experiment examining the response of the OR to increasing concentrations of odorant. Dose response curves can also assess how genetic variation in an OR affects in vitro odorant response8,9,11,35, and these studies can be extended to interspecific OR variation, allowing for the examination of receptor evolution across species and causal mutations in evolution36,37, Finally, this assay can be used to screen for odor antagonists that are able to antagonize OR response to a particular odorant for a known odorant/receptor pair38,39. In summary, this high-throughput luciferase assay is applicable to a range of studies that will help characterize OR activation patterns and provide a better understanding of odor coding in the olfactory system.

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			<td height="21" style="height:21px;width:265px;">Name of Material/ Equipment</td>
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			<td style="width:119px;">Catalog Number</td>
			<td style="width:167px;">Comments/Description</td>
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			<td height="84" style="height:84px;width:265px;">Hana3A cells</td>
			<td style="width:135px;">Avaiable from the Matsunami Laboratory upon request</td>
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			<td height="84" style="height:84px;width:265px;">RTP1S-pCI</td>
			<td style="width:135px;">Avaiable from the Matsunami Laboratory upon request</td>
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		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:265px;">M3-R-pCI</td>
			<td style="width:135px;">Avaiable from the Matsunami Laboratory upon request</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:265px;">pCRE-luc</td>
			<td style="width:135px;">Agilent</td>
			<td style="width:119px;">219076</td>
			<td><a href="http://www.chem.agilent.com/store/ProductDetail.aspx?productID=219076%28Agilent%29">LUC</a></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:265px;">pSV40-RL</td>
			<td style="width:135px;">Promega</td>
			<td style="width:119px;">E2231</td>
			<td><a href="http://www.promega.com/products/reporter-assays-and-transfection/reporter-vectors-and-cell-lines/prl-renilla-luciferase-control-reporter-vectors/">RL</a></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Minimum Essential Media, Eagle</td>
			<td>Sigma Aldrich</td>
			<td>M4655</td>
			<td><a href="http://www.sigmaaldrich.com/catalog/product/sigma/m4655?lang=en&amp;region=US">MEM</a></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:265px;">FBS</td>
			<td>Life Technologies</td>
			<td>16000-044</td>
			<td><a href="https://products.invitrogen.com/ivgn/product/16000044?ICID=search-16000044">FBS</a></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">PBS (without Ca2+ and Mg2+)</td>
			<td>Cellgro</td>
			<td>21-040-CV</td>
			<td><a href="http://cellgro.com/products/balanced-salt-solutions/phosphate-buffered-saline/phosphate-buffered-saline-1x-2.html">PBS</a></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Trypsin (0.05% Trypsin EDTA)</td>
			<td>Life Technologies</td>
			<td>25300</td>
			<td><a href="https://products.invitrogen.com/ivgn/product/25300054?ICID=search-product">Trypsin</a></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:265px;">CD293</td>
			<td>Life Technologies</td>
			<td>11913-019</td>
			<td><a href="http://products.invitrogen.com/ivgn/product/11913019?ICID=search-11913019">CD293</a></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:265px;">96 well PDL white/clear plate</td>
			<td style="width:135px;">BD BioCoat</td>
			<td style="width:119px;">356693</td>
			<td><a href="http://www.thomassci.com/Supplies/Tissue-Culture-Cellware/_/BD-Biocoat-Poly-D-Lysine-Culture-Dishes?q=356693">plates</a></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:265px;">Lipid transfection reagent: Lipofectamine 2000</td>
			<td>Life Technologies</td>
			<td>11668-019</td>
			<td><a href="https://products.invitrogen.com/ivgn/product/11668019?ICID=search-11668019">Lipofectamine</a></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:265px;">Firefly luciferase substrate, firefly luciferase quencher/Renilla luciferase substrate: Dual-Glo Assay</td>
			<td style="width:135px;">Promega</td>
			<td style="width:119px;">E2980</td>
			<td><a href="http://www.promega.com/products/reporter-assays-and-transfection/reporter-assays/dual_glo-luciferase-assay-system/?__utma=1.1932750276.1376486173.1376486173.1376486173.1&amp;__utmb=1.1.10.1376486173&amp;__utmc=1&amp;__utmx=-&amp;__utmz=1.1376486173.1.1.utmcsr=google|utmc">dual glo</a></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Synergy S2&#160;</td>
			<td style="width:135px;">BioTek</td>
			<td style="width:119px;">SLAD</td>
			<td><a href="http://www.biotek.com/products/microplate_detection/synergy2_multimode_microplate_reader.html">BioTek S2</a></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:265px;">Microplate reader software: Gen5 Data Analysis Software</td>
			<td style="width:135px;">BioTek</td>
			<td style="width:119px;">Gen5</td>
			<td><a href="http://www.biotek.com/products/microplate_software/gen5_data_analysis_software.html">Gen5</a></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:265px;">BIOSTACK</td>
			<td style="width:135px;">BioTek</td>
			<td style="width:119px;">BIOSTACK2WR</td>
			<td><a href="http://www.biotek.com/products/microplate_software/biostack_microplate_stacker.html">BioStack</a></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:265px;">Multiflo</td>
			<td style="width:135px;">BioTek</td>
			<td style="width:119px;">MFP</td>
			<td><a href="http://www.biotek.com/products/liquid_handling/multiflo_microplate_dispenser.html">MultiFlo</a></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:265px;">300ul GripTips</td>
			<td style="width:135px;">Integra</td>
			<td style="width:119px;">4433</td>
			<td><a href="http://www.integra-biosciences.com/sites/us/pipette_tips_griptips_4_e.html">GripTips</a></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:265px;">12.5ul GripTips</td>
			<td style="width:135px;">Integra</td>
			<td style="width:119px;">4414</td>
			<td><a href="http://www.integra-biosciences.com/sites/us/pipette_tips_griptips_4_e.html">GripTips</a></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:265px;">300ul GripTips ViaFlo96</td>
			<td style="width:135px;">Integra</td>
			<td style="width:119px;">6433</td>
			<td><a href="http://www.integra-biosciences.com/sites/us/pipette_tips_griptips_XYZ_4_e.html">XYZ tips</a></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:265px;">12.5ul GripTips 384 XYZ</td>
			<td style="width:135px;">Integra</td>
			<td style="width:119px;">6403</td>
			<td><a href="http://www.integra-biosciences.com/sites/us/pipette_tips_griptips_XYZ_4_e.html">XYZ tips</a></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:265px;">384ViaFlo</td>
			<td style="width:135px;">Integra</td>
			<td>6030</td>
			<td><a href="http://www.integra-biosciences.com/sites/us/96_384_channel_pipette.html">384ViaFlo</a></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">TE buffer</td>
			<td>Macherey Nagel</td>
			<td>740797.1</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">DMSO</td>
			<td>Sigma Aldrich</td>
			<td>D2650-100ML</td>
			<td><a href="http://www.sigmaaldrich.com/catalog/product/sigma/d2650?lang=en&amp;region=US">DMSO</a></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">forskolin</td>
			<td>Enzo Life Sciences</td>
			<td>BML-CN100-0010</td>
			<td><a href="http://www.thomassci.com/007635F0-AA41-4B24-B46A-05723D685997/_/FORSKOLIN-10MG?q=c002e24">FOR</a></td>
		</tr>
	</tbody>
</table>

high-throughput analysis of mammalian olfactory receptors: measurement of receptor activation via luciferase activity

Odorants create unique and overlapping patterns of olfactory receptor activation, allowing a family of approximately 1,000 murine and 400 human receptors to recognize thousands of odorants. Odorant ligands have been published for fewer than 6% of human receptors1-11. This lack of data is due in part to difficulties functionally expressing these receptors in heterologous systems. Here, we describe a method for expressing the majority of the olfactory receptor family in Hana3A cells, followed by high-throughput assessment of olfactory receptor activation using a luciferase reporter assay. This assay can be used to (1) screen panels of odorants against panels of olfactory receptors; (2) confirm odorant/receptor interaction via dose response curves; and (3) compare receptor activation levels among receptor variants. In our sample data, 328 olfactory receptors were screened against 26 odorants. Odorant/receptor pairs with varying response scores were selected and tested in dose response. These data indicate that a screen is an effective method to enrich for odorant/receptor pairs that will pass a dose response experiment, i.e. receptors that have a bona fide response to an odorant. Therefore, this high-throughput luciferase assay is an effective method to characterize olfactory receptors&#8212;an essential step toward a model of odor coding in the mammalian olfactory system.

A primary screen tested 328 ORs against 26 odors at a concentration of 100 &#181;M. This odor concentration has been demonstrated to effectively activate a large proportion of ORs with known ligands10. First, normalized luciferase activity was calculated by dividing the firefly luciferase reading by the Renilla luciferase reading. Next, baselined values were calculated by subtracting the normalized luciferase readings for the no odor control from the normalized luciferase readings for each well (<stro...

Watch this Scientific Journal Video about High-throughput Analysis of Mammalian Olfactory Receptors: Measurement of Receptor Activation via Luciferase Activity at JoVE.com

High-throughput Analysis of Mammalian Olfactory Receptors: Measurement of Receptor Activation via Luciferase Activity

Olfactory receptor activation patterns encode odor identity, but the lack of published data identifying odorant ligands for mammalian olfactory receptors hinders the development of a comprehensive model of odor coding. This protocol describes a method to facilitate high-throughput identification of olfactory receptor ligands and quantification of receptor activation.

Odorants create unique and overlapping patterns of olfactory receptor activation, allowing a family of approximately 1,000 murine and 400 human receptors ...

high-throughput-analysis-mammalian-olfactory-receptors-measurement

Research

JoVE Journal

Neuroscience

Slice Preparation, Organotypic Tissue Culturing and Luciferase Recording of Clock Gene Activity in the Suprachiasmatic Nucleus

A central circadian (~24 hr) clock coordinating daily rhythms in physiology and behavior resides in the suprachiasmatic nucleus (SCN) located in the anterior hypothalamus. The clock is directly synchronized by light via the retina and optic nerve. Circadian oscillations are generated by interacting negative feedback loops of a number of so called "clock genes" and their protein products, including the Period (Per) genes. The core clock is also dependent on membrane depolarization, calcium and cAMP 1. The SCN shows daily oscillations in clock gene expression, metabolic activity and spontaneous electrical activity. Remarkably, this endogenous cyclic activity persists in adult tissue slices of the SCN 2-4. In this way, the biological clock can easily be studied in vitro, allowing molecular, electrophysiological and metabolic investigations of the pacemaker function.
The SCN is a small, well-defined bilateral structure located right above the optic chiasm 5. In the rat it contains ~8.000 neurons in each nucleus and has dimensions of approximately 947 &mu;m (length, rostrocaudal axis) x 424 &mu;m (width) x 390 &mu;m (height) 6. To dissect out the SCN it is necessary to cut a brain slice at the specific level of the brain where the SCN can be identified. Here, we describe the dissecting and slicing procedure of the SCN, which is similar for mouse and rat brains. Further, we show how to culture the dissected tissue organotypically on a membrane 7, a technique developed for SCN tissue culture by Yamazaki et al. 8. Finally, we demonstrate how transgenic tissue can be used for measuring expression of clock genes/proteins using dynamic luciferase reporter technology, a method that originally was used for circadian measurements by Geusz et al. 9. We here use SCN tissues from the transgenic knock-in PERIOD2::LUCIFERASE mice produced by Yoo et al. 10. The mice contain a fusion protein of PERIOD (PER) 2 and the firefly enzyme LUCIFERASE. When PER2 is translated in the presence of the substrate for luciferase, i.e. luciferin, the PER2 expression can be monitored as bioluminescence when luciferase catalyzes the oxidation of luciferin. The number of emitted photons positively correlates to the amount of produced PER2 protein, and the bioluminescence rhythms match the PER2 protein rhythm in vivo 10. In this way the cyclic variation in PER2 expression can be continuously monitored real time during many days. The protocol we follow for tissue culturing and real-time bioluminescence recording has been thoroughly described by Yamazaki and Takahashi 11.

The procedure of preparing slices containing the adult mouse hypothalamic suprachiasmatic nucleus (SCN), and a rapid way to culture the SCN tissue in organotypic culture condition, are reported. Further, the measurement of oscillatory clock gene protein expression using dynamic luciferase reporter technology is described.

A central circadian (~24 hr) clock coordinating daily rhythms in physiology and behavior resides in the suprachiasmatic nucleus (SCN) located in the ...

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 ...

Odorant-induced Responses Recorded from Olfactory Receptor Neurons using the Suction Pipette Technique

Animals sample the odorous environment around them through the chemosensory systems located in the nasal cavity. Chemosensory signals affect complex behaviors such as food choice, predator, conspecific and mate recognition and other socially relevant cues. Olfactory receptor neurons (ORNs) are located in the dorsal part of the nasal cavity embedded in the olfactory epithelium. These bipolar neurons send an axon to the olfactory bulb (see Fig. 1, Reisert &amp; Zhao1, originally published in the Journal of General Physiology) and extend a single dendrite to the epithelial border from where cilia radiate into the mucus that covers the olfactory epithelium. The cilia contain the signal transduction machinery that ultimately leads to excitatory current influx through the ciliary transduction channels, a cyclic nucleotide-gated (CNG) channel and a Ca2+-activated Cl- channel (Fig. 1). The ensuing depolarization triggers action potential generation at the cell body2-4.
In this video we describe the use of the "suction pipette technique" to record odorant-induced responses from ORNs. This method was originally developed to record from rod photoreceptors5 and a variant of this method can be found at jove.com modified to record from mouse cone photoreceptors6. The suction pipette technique was later adapted to also record from ORNs7,8. Briefly, following dissociation of the olfactory epithelium and cell isolation, the entire cell body of an ORN is sucked into the tip of a recording pipette. The dendrite and the cilia remain exposed to the bath solution and thus accessible to solution changes to enable e.g. odorant or pharmacological blocker application. In this configuration, no access to the intracellular environment is gained (no whole-cell voltage clamp) and the intracellular voltage remains free to vary. This allows the simultaneous recording of the slow receptor current that originates at the cilia and fast action potentials fired by the cell body9. The difference in kinetics between these two signals allows them to be separated using different filter settings. This technique can be used on any wild type or knockout mouse or to record selectively from ORNs that also express GFP to label specific subsets of ORNs, e.g. expressing a given odorant receptor or ion channel.

Olfactory receptor neurons (ORNs) convert odor signals first into a receptor current that in turn triggers action potentials that are conveyed to second order neurons in the olfactory bulb. Here we describe the suction pipette technique to record simultaneously the odorant-induced receptor current and action potentials from mouse ORNs.

Animals sample the odorous environment around them through the chemosensory systems located in the nasal cavity. Chemosensory signals affect complex ...

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 ...

FIM Imaging and FIMtrack: Two New Tools Allowing High-throughput and Cost Effective Locomotion Analysis

The analysis of neuronal network function requires a reliable measurement of behavioral traits. Since the behavior of freely moving animals is variable to a certain degree, many animals have to be analyzed, to obtain statistically significant data. This in turn requires a computer assisted automated quantification of locomotion patterns. To obtain high contrast images of almost translucent and small moving objects, a novel imaging technique based on frustrated total internal reflection called FIM was developed. In this setup, animals are only illuminated with infrared light at the very specific position of contact with the underlying crawling surface. This methodology results in very high contrast images. Subsequently, these high contrast images are processed using established contour tracking algorithms. Based on this, we developed the FIMTrack software, which serves to extract a number of features needed to quantitatively describe a large variety of locomotion characteristics. During the development of this software package, we focused our efforts on an open source architecture allowing the easy addition of further modules. The program operates platform independent and is accompanied by an intuitive GUI guiding the user through data analysis. All locomotion parameter values are given in form of csv files allowing further data analyses. In addition, a Results Viewer integrated into the tracking software provides the opportunity to interactively review and adjust the output, as might be needed during stimulus integration. The power of FIM and FIMTrack is demonstrated by studying the locomotion of Drosophila larvae.

FIM is a novel, cost effective imaging system designed to track small moving objects such as C. elegans, planaria or Drosophila larvae. The accompanying FIMTrack program is designed to deliver fast and efficient data analysis. Together, these tools allow high-throughput analysis of behavioral traits.

The analysis of neuronal network function requires a reliable measurement of behavioral traits. Since the behavior of freely moving animals is variable to ...

Perforated Patch-clamp Recording of Mouse Olfactory Sensory Neurons in Intact Neuroepithelium: Functional Analysis of Neurons Expressing an Identified Odorant Receptor

Analyzing the physiological responses of olfactory sensory neurons (OSN) when stimulated with specific ligands is critical to understand the basis of olfactory-driven behaviors and their modulation. These coding properties depend heavily on the initial interaction between odor molecules and the olfactory receptor (OR) expressed in the OSNs. The identity, specificity and ligand spectrum of the expressed OR are critical. The probability to find the ligand of the OR expressed in an OSN chosen randomly within the epithelium is very low. To address this challenge, this protocol uses genetically tagged mice expressing the fluorescent protein GFP under the control of the promoter of defined ORs. OSNs are located in a tight and organized epithelium lining the nasal cavity, with neighboring cells influencing their maturation and function. Here we describe a method to isolate an intact olfactory epithelium and record through patch-clamp recordings the properties of OSNs expressing defined odorant receptors. The protocol allows one to characterize OSN membrane properties while keeping the influence of the neighboring tissue. Analysis of patch-clamp results yields&#160;a precise quantification of ligand/OR interactions, transduction pathways and pharmacology, OSNs&#39; coding properties and their modulation at the membrane level.&#160;

Analyzing the physiological properties of olfactory sensory neurons still faces technical limitations. Here we record them through perforated patch-clamp in an intact preparation of the olfactory epithelium in gene-targeted mice. This technique allows the characterization of membrane properties and responses to specific ligands of neurons expressing defined olfactory receptors.

Analyzing the physiological responses of olfactory sensory neurons (OSN) when stimulated with specific ligands is critical to understand the basis of ...

Receptor Autoradiography Protocol for the Localized Visualization of Angiotensin II Receptors

This protocol describes receptor binding patterns for Angiotensin II (Ang II) in the rat brain using a radioligand specific for Ang II receptors to perform receptor autoradiographic mapping.
Tissue specimens are harvested and stored at -80 &#176;C. A cryostat is used to coronally section the tissue (brain) and thaw-mount the sections onto charged slides. The slide-mounted tissue sections are incubated in 125I-SI-Ang II to radiolabel Ang II receptors. Adjacent slides are separated into two sets: &#39;non-specific binding&#39; (NSP) in the presence of a receptor saturating concentration of non-radiolabeled Ang II, or an AT1 Ang II receptor subtype (AT1R) selective Ang II receptor antagonist, and &#39;total binding&#39; with no AT1R antagonist. A saturating concentration of AT2 Ang II receptor subtype (AT2R) antagonist (PD123319, 10 &#181;M) is also present in the incubation buffer to limit 125I-SI-Ang II binding to the AT1R subtype. During a 30 min pre-incubation at ~22 &#176;C, NSP slides are exposed to 10 &#181;M PD123319 and losartan, while &#39;total binding&#39; slides are exposed to 10 &#181;M PD123319. Slides are then incubated with 125I-SI-Ang II in the presence of PD123319 for &#39;total binding&#39;, and PD123319 and losartan for NSP in assay buffer, followed by several &#39;washes&#39; in buffer, and water to remove salt and non-specifically bound radioligand. The slides are dried using blow-dryers, then exposed to autoradiography film using a specialized film and cassette. The film is developed and the images are scanned into a computer for visual and quantitative densitometry using a proprietary imaging system and a spreadsheet. An additional set of slides are thionin-stained for histological comparisons.
The advantage of using receptor autoradiography is the ability to visualize Ang II receptors in situ, within a section of a tissue specimen, and anatomically identify the region of the tissue by comparing it to an adjacent histological reference section.

Here we present a protocol to describe the localization of angiotensin II Type 1 receptors in the rat brain by quantitative, densitometric, in vitro receptor autoradiography using an iodine-125 labeled analog of angiotensin II.

This protocol describes receptor binding patterns for Angiotensin II (Ang II) in the rat brain using a radioligand specific for Ang II receptors to ...

Recording Temperature-induced Neuronal Activity through Monitoring Calcium Changes in the Olfactory Bulb of Xenopus laevis

The olfactory system, specialized in the detection, integration and processing of chemical molecules is likely the most thoroughly studied sensory system. However, there is piling evidence that olfaction is not solely limited to chemical sensitivity, but also includes temperature sensitivity. Premetamorphic Xenopus laevis are translucent animals, with protruding nasal cavities deprived of the cribriform plate separating the nose and the olfactory bulb. These characteristics make them well suited for studying olfaction, and particularly thermosensitivity. The present article describes the complete procedure for measuring temperature responses in the olfactory bulb of X. laevis larvae. Firstly, the electroporation of olfactory receptor neurons (ORNs) is performed with spectrally distinct dyes loaded into the nasal cavities in order to stain their axon terminals in the bulbar neuropil. The differential staining between left and right receptor neurons serves to identify the &#947;-glomerulus as the only structure innervated by contralateral presynaptic afferents. Secondly, the electroporation is combined with focal bolus loading in the olfactory bulb in order to stain mitral cells and their dendrites. The 3D brain volume is then scanned under line-illumination microscopy for the acquisition of fast calcium imaging data while small temperature drops are induced at the olfactory epithelium. Lastly, the post-acquisition analysis allows the morphological reconstruction of the thermosensitive network comprising the &#947;-glomerulus and its innervating mitral cells, based on specific temperature-induced Ca2+ traces. Using chemical odorants as stimuli in addition to temperature jumps enables the comparison between thermosensitive and chemosensitive networks in the olfactory bulb.

Recording Temperature-induced Neuronal Activity through Monitoring Calcium Changes in the Olfactory Bulb of Xenopus laevis

Here we describe a protocol for measuring and analyzing temperature responses in the olfactory bulb of Xenopus laevis. Olfactory receptor neurons and mitral cells are differentially stained, after which calcium changes are recorded, reflecting a sensitivity of some neural networks in the bulb to temperature drops induced at the nose.

The olfactory system, specialized in the detection, integration and processing of chemical molecules is likely the most thoroughly studied sensory system. ...

Live-cell Measurement of Odorant Receptor Activation Using a Real-time cAMP Assay

The enormous sizes of the mammalian odorant receptor (OR) families present difficulties to find their cognate ligands among numerous volatile chemicals. To efficiently and accurately deorphanize ORs, we combine the use of a heterologous cell line to express mammalian ORs and a genetically modified biosensor plasmid to measure cAMP production downstream of OR activation in real time. This assay can be used to screen odorants against ORs and vice versa. Positive odorant-receptor interactions from the screens can be subsequently confirmed by testing against various odor concentrations, generating concentration-response curves. Here we used this method to perform a high-throughput screening of an odorous compound against a human OR library expressed in Hana3A cells and confirmed that the positively-responding receptor is the cognate receptor for the compound of interest. We found this high-throughput detection method to be efficient and reliable in assessing OR activation and our data provide an example of its potential use in OR functional studies.

Characterizing the function of odorant receptors serves an indispensable part in the deorphanization process. We describe a method to measure the activation of odorant receptors in real time using a cAMP assay.

The enormous sizes of the mammalian odorant receptor (OR) families present difficulties to find their cognate ligands among numerous volatile chemicals. ...

High-throughput Analysis of Locomotor Behavior in the Drosophila Island Assay

Advances in next-generation sequencing technologies contribute to the identification of (candidate) disease genes for movement disorders and other neurological diseases at an increasing speed. However, little is known about the molecular mechanisms that underlie these disorders. The genetic, molecular, and behavioral toolbox of Drosophila melanogaster makes this model organism particularly useful to characterize new disease genes and mechanisms in a high-throughput manner. Nevertheless, high-throughput screens require efficient and reliable assays that, ideally, are cost-effective and allow for the automatized quantification of traits relevant to these disorders. The island assay is a cost-effective and easily set-up method to evaluate Drosophila locomotor behavior. In this assay, flies are thrown onto a platform from a fixed height. This induces an innate motor response that enables the flies to escape from the platform within seconds. At present, quantitative analyses of filmed island assays are done manually, which is a laborious undertaking, particularly when performing large screens.
This manuscript describes the &#34;Drosophila Island Assay&#34; and &#34;Island Assay Analysis&#34; algorithms for&#160;high-throughput, automated data processing and quantification of island assay data. In the setup, a simple webcam connected to a laptop collects an image series of the platform while the assay is performed. The &#34;Drosophila Island Assay&#34; algorithm developed for the open-source software Fiji processes these image series and quantifies, for each experimental condition, the number of flies on the platform over time. The &#34;Island Assay Analysis&#34; script, compatible with the free software R, was developed to automatically process the obtained data and to calculate whether treatments/genotypes are statistically different. This greatly improves the efficiency of the island assay and makes it a powerful readout for basic locomotion and flight behavior. It can thus be applied to large screens investigating fly locomotor ability, Drosophila models of movement disorders, and drug efficacy.

High-throughput Analysis of Locomotor Behavior in the Drosophila Island Assay

The island assay is a relatively new, cost-effective assay that can be used to evaluate the basic locomotor behavior of Drosophila melanogaster. This manuscript describes algorithms for automatic data processing and objective quantification of island assay data, making this assay a sensitive, high-throughput readout for large genetic or pharmacological screens.