Name: characterizing the composition of molecular motors on moving axonal cargo using "cargo mapping" analysis
Uploaded: 2014-10-30T13:00:00
Description: Watch this Scientific Journal Video about Characterizing the Composition of Molecular Motors on Moving Axonal Cargo Using "Cargo Mapping" Analysis at JoVE.com

We thank Ge Yang, Gaudenz Danuser, Khuloud Jaqaman, and Daniel Whisler for assistance with the adaptation and development of the software to quantitate cargo mapping analyses, and Emily Niederst for help in making the microfluidic devices. This work was supported in part by NIH-NIA grant AG032180 to L.S.B.G., and the Howard Hughes Medical Institute. L.S. was supported in part by a NIH Bioinformatics Training Grant T32 GM008806, S.E.E. was supported by a Damon Runyon Cancer Research Foundation Fellowship, NIH Neuroplasticity Training Grant AG000216, and by a grant from The Ellison Medical Foundation New Scholar in Aging Award, G.E.C was supported by an NIH/NCATS&#160;1 TL1 award TR001114 and by the Achievement Rewards for College Scientists foundation.

All experiments were conducted following approved protocols and according to institutional guidelines for the humane care of research animals. Neonate mice were euthanized by decapitation.
1. Preparation of Microfluidic Devices for Cell Culture
<ol>
	<li>Prepare polydimethyl siloxane (PDMS) microfluidic devices for growth of hippocampal neurons as described by Harris and colleagues17-19. Below are some modifications that were adapted to the cargo mapping protocol. 
	NOTE: Mic...

<ol>
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The protocol presented here enables the correlation of directionality of movement of individual fluorescent microtubule-based moving cargo particles with the relative type and amount of associated motor proteins in live neurons. Previously, the total motor composition of axonal vesicular cargoes was assayed on heterogeneous populations of biochemically purified vesicles and organelles9,15. However, characterizing motor composition for a single type of cargo inside cells has been chal...

Intracellular transport is critical in all cell types for the delivery of proteins, membranes, organelles, and signaling molecules to various cellular domains1. Neurons are highly specialized cells with long, polarized projections that critically depend on intracellular transport of essential cargoes for their long-distance delivery to various axonal microdomains. This transport is mediated by kinesins and dyneins &#8212; two large families of molecular motor proteins &#8212; that bind to cargoes and track along polarized microtubules in anterograde and retrograde directions, respectively. While retrograde movement is mainly mediated by dynein, movement in the anterograde direction is facilitated by a large, functionally diverse family of kinesin motors. Consequently, anterograde transport of axonal cargoes could be mediated by various family members of the kinesin superfamily1-5. Though some cargoes move persistently in either direction, most cargoes move bidirectionally and reverse frequently on their way to their final destinations1,5-13. Furthermore, it has been shown that motors of opposing directionality associate simultaneously to cargoes, raising the question as to how regulated movement of cargoes is coordinated by opposite-polarity motors5-7. Together, transport of axonal cargoes is a concerted process that is regulated by the composition of motors and their specific biochemical activities, which in turn are dependent on various adaptors and regulatory binding partners14.
To faithfully describe the mechanism of axonal transport for a specific cargo and to uncover the underlying regulation of that transport, it is paramount to determine the composition of motor proteins and their regulatory binding partners associated with individual cargoes during their live transport. Other methods, for example biochemical approaches, provide estimates of average motor compositions on purified heterogeneous vesicle populations, but these estimates do not reveal the type or amounts of motors associated to single moving vesicles. Also, reconstitution of vesicle transport along preassembled microtubules in vitro enabled measuring the amount of one type of motor on a single vesicle level15. However, these experiments did not directly correlate the amount of motors with the transport characteristics of those vesicles, and measured transport in the absence of cellular regulatory factors.
A protocol is presented here, which determines the motor composition (type and relative amount of motors) of individual moving vesicles from immunofluorescence (IF) data measuring endogenously expressed motor proteins, and correlates these parameters to the live transport of the exact same vesicles in neurons16. This method entails precise mapping of IF-to-live cargo movement data. This is accomplished by growing hippocampal mouse neurons in microfluidic devices following established protocols17-19. These devices allow for the identification and correlation (&#8220;mapping&#8221;) of axons and single moving cargoes in fixed and live light microscopy modalities (Figure 1). Cultured neurons are transfected with fluorescently labeled cargo proteins whose transport is imaged at high spatial and temporal resolution to obtain detailed movement information that is plotted in kymographs. During the course of imaging, neurons are fixed with paraformaldehyde, and subsequently stained with antibodies against endogenous motor proteins. Fixed cargo and motor images are superimposed onto live movement kymographs to &#8220;map&#8221; (colocalize) them to the live cargo movement trajectories16. To correlate the live movement of cargoes with the association of motor proteins, colocalization is analyzed using a custom made MATLAB software package called &#8220;Motor Colocalization&#8221;16,20. Fluorescently labeled cargoes and motors generate diffraction-limited punctate features that can partially overlap. To resolve the position of overlapping puncta, the software first automatically fits Gaussian functions to each point spread function, representing individual fluorescent puncta, to determine their precise X-Y sub-pixel position coordinates and intensity amplitudes21-23. The positions of motors and cargoes are subsequently compared to each other to determine colocalization16,20. Therefore, this method more precisely assigns colocalization between fluorescent puncta as compared to other methods24.
The strength of this method is the ability to assess the colocalization of motors with individual cargo in fixed cells, for which live movement trajectories (e.g., the direction in which they were moving at the time of fixation) have been recorded. With this method, kinesins and dyneins were found to associate simultaneously to vesicles that carry the normal prion protein (PrPC-cellular), a neuronally enriched cargo that moves bidirectionally or remains stationary in axons16. This analysis allowed the formulation of a working model for the regulation of PrPC vesicle movement in which anterograde (kinesin) and retrograde (dynein) motors coordinate their activities in order to move the vesicles in either direction or to remain stationary while associated to the cargo. Another strength of this method is its potential broad applicability for characterizing colocalization/association of many fluorescently labeled cargoes that move in virtually any cell type, with any other protein(s) of interest. Thus, live/fixed correlation could potentially allow for the detection of transient protein-cargo interactions, as many individual fluorescently labeled moving particles can be analyzed over a desired period of time. Given the broad applicability and the type of questions that this method can address, this protocol will be of interest to a wide audience of cell biologists including those studying trafficking and transport in neurons or in other cell types.

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			<td>P5899-20mg</td>
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			<td height="21" style="height:21px;">D-MEM (Dulbecco&#8217;s Modified Eagle Medium) High Glucose, w/ L-Glutamine, w/o Sodium Pyruvate (1X)</td>
			<td>Life Technologies</td>
			<td>11965092</td>
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			<td>24020117</td>
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			<td height="21" style="height:21px;">DPBS (Dulbecco&#8217;s Phosphate Buffered Saline, no Magnesium, no Calcium (1X)</td>
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			<td>14190250</td>
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			<td height="21" style="height:21px;">Penicillin/Streptomycin (100X)</td>
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			<td>15140122</td>
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			<td height="21" style="height:21px;">Corning cellgro Water for Cell Culture&#160;</td>
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			<td height="21" style="height:21px;">Lipofectamine 2000</td>
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			<td height="21" style="height:21px;">Formaldehyde Solution 16% EM Grade</td>
			<td>Fisher Scientific</td>
			<td>50980487</td>
			<td>Caution: Harmful by inhalation, in contact with skin and if swallowed. Irritating to eyes, respiratory system and skin. Dispose according to official regulations.</td>
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			<td height="21" style="height:21px;">Sucrose</td>
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			<td>BP2818-100</td>
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			<td height="21" style="height:21px;">ProLong Gold antifade reagent</td>
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			<td height="21" style="height:21px;">Cover Glass 1 1/2. 24X40mm</td>
			<td>Corning</td>
			<td>2980-244</td>
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			<td height="21" style="height:21px;">Axis microfluidic device, 450 &#181;m</td>
			<td>Millipore</td>
			<td>AX450</td>
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			<td height="21" style="height:21px;">Adobe Photoshop</td>
			<td>Adobe</td>
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			<td height="21" style="height:21px;">60 mm cell culture dish</td>
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			<td height="21" style="height:21px;">150 mm cell culture dish</td>
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			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;"></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Antibodies Used:</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Anti-Kinesin light chain, V-17</td>
			<td>Santa Cruz&#160;</td>
			<td>sc-13362</td>
			<td>specificity verified using KLC1-/- neurons (Ref. 16 ), recommended dilution 1:100.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Anti Dynein Heavy Chain 1, R-325</td>
			<td>Santa Cruz&#160;</td>
			<td>sc-9115</td>
			<td>specificity verified using shRNA against DYN1HC1 (Ref. 16), recommended dilution 1:100</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Alexa Fluor 568 Donkey Anti-Rabbit IgG Antibody</td>
			<td>Life Technologies</td>
			<td>A10042</td>
			<td>&#160;recommended dilution 1:200.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Alexa Fluor 647 Donkey Anti-Rabbit IgG (H+L) Antibody</td>
			<td>Life Technologies</td>
			<td>A31573</td>
			<td>&#160;recommended dilution 1:200.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Alexa Fluor 568 Donkey Anti-Goat IgG (H+L) Antibody IgG Antibody</td>
			<td>Life Technologies</td>
			<td>A11057</td>
			<td>&#160;recommended dilution 1:200.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Alexa Fluor 647 Donkey Anti-Goat IgG (H+L) Antibody</td>
			<td>Life Technologies</td>
			<td>A21447</td>
			<td>&#160;recommended dilution 1:200.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;"></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;"></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Plugins and Macros</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">ImageJ</td>
			<td></td>
			<td></td>
			<td><a href="http://imagej.nih.gov/ij/index.html">&#160;http://imagej.nih.gov/ij/index.html.&#160;</a></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">ImageJ Kymoraph Plugin</td>
			<td></td>
			<td></td>
			<td><a href="http://www.embl.de/eamnet/html/body_kymograph.html">http://www.embl.de/eamnet/html/body_kymograph.html.</a></td>
		</tr>
	</tbody>
</table>

characterizing the composition of molecular motors on moving axonal cargo using "cargo mapping" analysis

Understanding the mechanisms by which molecular motors coordinate their activities to transport vesicular cargoes within neurons requires the quantitative analysis of motor/cargo associations at the single vesicle level. The goal of this protocol is to use quantitative fluorescence microscopy to correlate (&#8220;map&#8221;) the position and directionality of movement of live cargo to the composition and relative amounts of motors associated with the same cargo. &#8220;Cargo mapping&#8221; consists of live imaging of fluorescently labeled cargoes moving in axons cultured on microfluidic devices, followed by chemical fixation during recording of live movement, and subsequent immunofluorescence (IF) staining of the exact same axonal regions with antibodies against motors. Colocalization between cargoes and their associated motors is assessed by assigning sub-pixel position coordinates to motor and cargo channels, by fitting Gaussian functions to the diffraction-limited point spread functions representing individual fluorescent point sources. Fixed cargo and motor images are subsequently superimposed to plots of cargo movement, to &#8220;map&#8221; them to their tracked trajectories. The strength of this protocol is the combination of live and IF data to record both the transport of vesicular cargoes in live cells and to determine the motors associated to these exact same vesicles. This technique overcomes previous challenges that use biochemical methods to determine the average motor composition of purified heterogeneous bulk vesicle populations, as these methods do not reveal compositions on single moving cargoes. Furthermore, this protocol can be adapted for the analysis of other transport and/or trafficking pathways in other cell types to correlate the movement of individual intracellular structures with their protein composition. Limitations of this protocol are the relatively low throughput due to low transfection efficiencies of cultured primary neurons and a limited field of view available for high-resolution imaging. Future applications could include methods to increase the number of neurons expressing fluorescently labeled cargoes.

Figure 1 shows an overview of the microfluidic device used to grow hippocampal neurons (Figure 1A, B). Neurons are plated in reservoir 1. The size of the microchannels prevents the diffusion of cell bodies (soma) into the axonal compartment while the length of the channels prevents dendritic projections from crossing all the way to the axonal compartment. After ~2-3 days in culture, neurons start extending their axons across microchannels into the axonal compartment (Figure 1B, C...

Watch this Scientific Journal Video about Characterizing the Composition of Molecular Motors on Moving Axonal Cargo Using "Cargo Mapping" Analysis at JoVE.com

Characterizing the Composition of Molecular Motors on Moving Axonal Cargo Using "Cargo Mapping" Analysis

Intracellular transport of cargoes, such as vesicles or organelles, is carried out by molecular motor proteins that track on polarized microtubules. This protocol describes the correlation of the directionality of transport of individual cargo particles moving inside neurons, to the relative amount and type of associated motor proteins.

Understanding the mechanisms by which molecular motors coordinate their activities to transport vesicular cargoes within neurons requires the quantitative ...

Research

JoVE Journal

Neuroscience

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