Name: utilizing combined methodologies to define the role of plasma membrane delivery during axon branching and neuronal morphogenesis
Uploaded: 2016-03-16T14:00:00
Description: Watch this Scientific Journal Video about Utilizing Combined Methodologies to Define the Role of Plasma Membrane Delivery During Axon Branching and Neuronal Morphogenesis at JoVE.com

This work was supported by the National Institutes of Health: RO1-GM108970 (SLG) and F31-NS087837 (CW).

Statement of research ethics: All experiments involving animals detailed herein are subject to the rules and regulations of the UNC Committee on Animal Care and to NIH standards for the care and use of laboratory animals.
1. Preparation and Plating of Dissociated Cortical Neurons
<ol>
	<li>Euthanize timed-pregnant females by CO2 inhalation followed by cervical dislocation. Remove whole brains from the skulls of embryonic day 15.5 (E15.5) mice and microdissect cort...

<ol>
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Axon branching is a fundamental neurodevelopmental process and underpins the vast neuroconnectivity of the mammalian nervous system. Understanding the mechanisms involved in localized plasma membrane expansion is integral to our understanding of both normal and pathological neurodevelopment. The use of a multipronged approach incorporating both population level and single cell level methodologies enhances reproducibility and increases spatial and temporal resolution without compromising population level analysis. At the ...

Recent estimates suggest that the human brain contains 1011 neurons with 1014 synaptic connections1, highlighting the importance of axon branching in vivo. Extracellular axon guidance cues such as netrin-1 guide axons to appropriate synaptic partners and stimulate axonal branching, thereby increasing synaptic capacity2-5. Netrin-1-dependent axonal arborization involves substantial plasma membrane expansion6, which we hypothesized requires delivery of additional membrane components via SNARE complex dependent exocytic vesicle fusion7. 
Investigating the role of SNARE-mediated exocytosis in netrin-1 dependent axon branching is complicated by several factors. First, the heterogeneity of cortical neurons increases the sample size required to identify significant effects, complicating single cell techniques like imaging. Second, although biochemical techniques permit observation of changes that occur at the population level, they lack the temporal and spatial resolution necessary to localize plasma membrane expansion to the axon in the time frame of axon branching. Lastly, although axon branches form over hours, the cellular changes that contribute to axonal extension may begin within minutes and occur on the order of seconds, thus extending the temporal scope for experimental consideration. 
We outline a multi-technique approach that addresses these diverse temporal and spatial scales of exocytosis and axon branching, and thus enhances our understanding of the fundamental cellular mechanisms. Utilizing these approaches provides evidence that supports a critical role for SNARE-mediated exocytosis in axon branching.

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			<td height="40" style="height:40px;width:179px;">6-well tissue culture treated plates</td>
			<td style="width:99px;">Olympus Plastics</td>
			<td style="width:76px;">25-105</td>
			<td style="width:187px;"></td>
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			<td height="141" style="height:141px;width:179px;">glass coverslips</td>
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			<td style="width:187px;">12CIR-1.5;must be nitric acid treated for 24 hours, rinsed in DI H2O 2X, and dried prior to use. Must be coated with 1mg/mL Poly-d-lysine and rinsed prior to plating cells</td>
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			<td height="41" style="height:41px;width:179px;">Amaxa nucleofection solution</td>
			<td style="width:99px;">Lonza</td>
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			<td style="width:187px;">100ml/transfection</td>
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			<td height="61" style="height:61px;width:179px;">Amaxa Nucleofector/electroporator</td>
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			<td height="81" style="height:81px;width:179px;">35mm Glass bottom live cell imaging dishes</td>
			<td style="width:99px;">Matek Corporation</td>
			<td style="width:76px;">p356-1.5-14-C</td>
			<td style="width:187px;">must be coated with 1mg/mL Poly-d-lysine and rinsed prior to plating cells</td>
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			<td height="41" style="height:41px;width:179px;">Olympus IX81-ZDC2 inverted microscope</td>
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			<td height="41" style="height:41px;width:179px;">100x 1.49 NA TIRF objective</td>
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			<td style="width:76px;"></td>
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			<td style="width:187px;">Used for scanning blots</td>
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			<td style="width:187px;">Used for scanning on the Odyssey Infrared system; Image studio lite used for offline analysis of blots</td>
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			<td height="61" style="height:61px;width:179px;">Metamorph for Olympus</td>
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			<td height="41" style="height:41px;width:179px;">40x 1.4 NA Plan Apochromat objective</td>
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			<td style="width:76px;"></td>
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			<td height="61" style="height:61px;width:179px;">Neurobasal media</td>
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			<td style="width:187px;">Base solution for both serum free and trypsin quenching media</td>
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			<td height="62" style="height:62px;width:179px;">Supplement B27</td>
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			<td style="width:187px;">500ml/50mLs Serum free media and Trypsin Quenching media</td>
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			<td height="21" style="height:21px;width:179px;">10X&#160; trypsin</td>
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			<td height="21" style="height:21px;width:179px;">HEPES</td>
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			<td height="61" style="height:61px;width:179px;">Dulbecco&#39;s Phosphate Buffered Saline (DPBS)+ Ca + Mg</td>
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			<td height="42" style="height:42px;width:179px;">Poly-D-Lysine</td>
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			<td style="width:187px;">Dissolved in sterile water at 1mg/mL</td>
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		<tr height="81">
			<td height="81" style="height:81px;width:179px;">Botulinum A toxin BoNTA</td>
			<td style="width:99px;">List Biological Laboratories</td>
			<td style="width:76px;">128-A</td>
			<td style="width:187px;"></td>
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		<tr height="41">
			<td height="41" style="height:41px;width:179px;">Rabbit polyclonal anti human VAMP2</td>
			<td style="width:99px;">Cell signaling</td>
			<td style="width:76px;">11829</td>
			<td style="width:187px;"></td>
		</tr>
		<tr height="61">
			<td height="61" style="height:61px;width:179px;">Mouse monoclonal anti rat Syntaxin1A</td>
			<td style="width:99px;">Santa Cruz Biotechnology</td>
			<td>sc-12736</td>
			<td style="width:187px;"></td>
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		<tr height="61">
			<td height="61" style="height:61px;width:179px;">Goat polyclonal anti human SNAP-25</td>
			<td style="width:99px;">Santa Cruz Biotechnology</td>
			<td>sc-7538</td>
			<td style="width:187px;"></td>
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			<td height="41" style="height:41px;width:179px;">Mouse monoclonal anti human &#946;III-tubulin&#160;</td>
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			<td height="81" style="height:81px;width:179px;">Alexa Fluor 568 and Alexa Fluor 488 phalloidin, or Alexa Fluor 647</td>
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			<td style="width:76px;"></td>
			<td style="width:187px;"></td>
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		<tr height="121">
			<td height="121" style="height:121px;width:179px;">LI-COR IR-dye secondary antibodies</td>
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			<td style="width:76px;">P/N 925-32212,P/N 925-68023, P/N 926-68022</td>
			<td style="width:187px;">800 donkey anti-mouse, 680 donkey anti rabbit, 680 donkey anti goat</td>
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		<tr height="61">
			<td height="61" style="height:61px;width:179px;">0.2um pore size nitrocellulose membrane</td>
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			<td style="width:76px;">9004-70-0</td>
			<td style="width:187px;"></td>
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			<td height="41" style="height:41px;width:179px;">Sucrose</td>
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		<tr height="41">
			<td height="41" style="height:41px;width:179px;">Paraformaldehyde</td>
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			<td style="width:76px;">O-4042-500</td>
			<td style="width:187px;"></td>
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			<td height="41" style="height:41px;width:179px;">Triton-X100</td>
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			<td height="41" style="height:41px;width:179px;">40% Bis-Acrylimide</td>
			<td style="width:99px;">Fisher scientific</td>
			<td style="width:76px;">BP1408-1</td>
			<td style="width:187px;"></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:179px;">Name</td>
			<td style="width:99px;">Company</td>
			<td style="width:76px;">Catalog Number</td>
			<td style="width:187px;">Comments</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:179px;">Alternative Validated Antibodies</td>
			<td style="width:99px;"></td>
			<td style="width:76px;"></td>
			<td style="width:187px;"></td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:179px;">Mouse Monoclonal Anti-Syntaxin HPC-1 clone</td>
			<td style="width:99px;">Sigma Aldrich</td>
			<td style="width:76px;">S0664</td>
			<td style="width:187px;"></td>
		</tr>
		<tr height="61">
			<td height="61" style="height:61px;width:179px;">&#160;Mouse Monoclonal Synaptobrevin 2 (VAMP2)</td>
			<td style="width:99px;">Synaptic Systems</td>
			<td style="width:76px;">104-211</td>
			<td style="width:187px;"></td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:179px;">Mouse Monoclonal SNAP25</td>
			<td style="width:99px;">Synaptic Systems</td>
			<td style="width:76px;">111-011</td>
			<td style="width:187px;"></td>
		</tr>
	</tbody>
</table>

utilizing combined methodologies to define the role of plasma membrane delivery during axon branching and neuronal morphogenesis

During neural development, growing axons extend to multiple synaptic partners by elaborating axonal branches. Axon branching is promoted by extracellular guidance cues like netrin-1 and results in dramatic increases to the surface area of the axonal plasma membrane. Netrin-1-dependent axon branching likely involves temporal and spatial control of plasma membrane expansion, the components of which are supplied through exocytic vesicle fusion. These fusion events are preceded by formation of SNARE complexes, comprising a v-SNARE, such as VAMP2 (vesicle-associated membrane protein 2), and plasma membrane t-SNAREs, syntaxin-1 and SNAP25 (synaptosomal-associated protein 25). Detailed herein isa multi-pronged approach used to examine the role of SNARE mediated exocytosis in axon branching. The strength of the combined approach is data acquisition at a range of spatial and temporal resolutions, spanning from the dynamics of single vesicle fusion events in individual neurons to SNARE complex formation and axon branching in populations of cultured neurons. This protocol takes advantage of established biochemical approaches to assay levels of endogenous SNARE complexes and Total Internal Reflection Fluorescence (TIRF) microscopy of cortical neurons expressing VAMP2 tagged with a pH-sensitive GFP (VAMP2-pHlourin) to identify netrin-1 dependent changes in exocytic activity in individual neurons. To elucidate the timing of netrin-1-dependent branching, time-lapse differential interference contrast (DIC) microscopy of single neurons over the order of hours is utilized. Fixed cell immunofluorescence paired with botulinum neurotoxins that cleave SNARE machinery and block exocytosis demonstrates that netrin-1 dependent axon branching requires SNARE-mediated exocytic activity.

Utilizing in vitro biochemical techniques to assay the amount of SDS-resistant SNARE complexes in a population of neurons. Figure 1 shows the resulting western blot following completion of the SDS-resistant SNARE complex assay probed for SNAP-25, syntaxin1A and VAMP2.
TIRF microscopy at the basal cell membrane provides high resolution images of individual exocytic fusion events in single cells. ...

Watch this Scientific Journal Video about Utilizing Combined Methodologies to Define the Role of Plasma Membrane Delivery During Axon Branching and Neuronal Morphogenesis at JoVE.com

Utilizing Combined Methodologies to Define the Role of Plasma Membrane Delivery During Axon Branching and Neuronal Morphogenesis

Light microscopy techniques coupled with biochemical assays elucidate the involvement of SNARE-mediated exocytosis in netrin-dependent axon branching. This combination of techniques permits identification of molecular mechanisms controlling axon branching and cell shape change.

During neural development, growing axons extend to multiple synaptic partners by elaborating axonal branches. Axon branching is promoted by extracellular ...

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JoVE Journal

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