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Investigating Mammalian Axon Regeneration: In Vivo Electroporation of Adult Mouse Dorsal Root Ganglion

Published: September 1st, 2018



1Department of Orthopaedic Surgery, Johns Hopkins University School of Medicine, 2The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine

Electroporation is an effective approach to deliver genes of interests into cells. By applying this approach in vivo on the neurons of adult mouse dorsal root ganglion (DRG), we describe a model to study axon regeneration in vivo.

Electroporation is an essential non-viral gene transfection approach to introduce DNA plasmids or small RNA molecules into cells. A sensory neuron in the dorsal root ganglion (DRGs) extends a single axon with two branches. One branch goes to the peripheral nerve (peripheral branch), and the other branch enters the spinal cord through the dorsal root (central branch). After the neural injury, the peripheral branch regenerates robustly whereas the central branch does not regenerate. Due to the high regenerative capacity, sensory axon regeneration has been widely used as a model system to study mammalian axon regeneration in both the peripheral nervous system (PNS) and the central nervous system (CNS). Here, we describe a previously established approach protocol to manipulate gene expression in mature sensory neurons in vivo via electroporation. Based on transfection with plasmids or small RNA oligos (siRNAs or microRNAs), the approach allows for both loss- and gain-of-function experiments to study the roles of genes-of-interests or microRNAs in regulation of axon regeneration in vivo. In addition, the manipulation of gene expression in vivo can be controlled both spatially and temporally within a relatively short time course. This model system provides a unique tool to investigate the molecular mechanisms by which mammalian axon regeneration is regulated in vivo.

Injuries in the nervous system caused by neural trauma or various neurodegenerative diseases usually result in defects in motor, sensory and cognitive functions. Recently, much effort has been devoted to regenerative potency re-establishment in adult neurons to restore the physiological functionsof injured neurons1,2,3. Sensory neurons in the DRG are a cluster of nerve cells that convey different sensory stimuli, such as pain, temperature, touch, or body posture, to the brain. Each of these neurons is pseudo-unipolar and contains a single axon that bifurcates with one branch ....

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All animal experiments were performed in accordance with the animal protocol approved by the Johns Hopkins Institutional Animal Care and Use Committee.

1. Materials and Reagents

  1. Animals
    1. Use six-week-old female CF1 mice weighing 30–35 g for the experiments.
      NOTE: The mice were group-housed (5 mice per cage) in individually ventilated sterilized cages with 1/4” corn cob bedding and 2” square nestlets for nesting. The cages were m.......

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To quantify the cytotoxicity of the current protocol and to validate that transfection rate of in vivo DRG electroporation is high enough, we injected and electroporated fluorescently-tagged microRNA or siRNA into L4 and L5 DRGs. The detached DRGs were processed through cryo-sectioning and immunohistochemistry (Figure 1A-B). When estimating the cell survival rate after injection and electroporation, the intact DRGs from L4 and L5 wer.......

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Several surgical steps require particular attention. The L4 and L5 DRGs (location of somas), which dominate the sciatic nerve, need to be correctly identified and injected with gene constructs. Otherwise, the GFP-labeling will be absent in sciatic nerve axons. The iliac crests can be viewed as useful anatomical landmarks to pinpoint L4 and L5 DRGs. In most mice, the facet joint between L5 and L6 vertebrae is proximate to iliac crests12. Alternatively, L3 DRG can be chosen instead of L5, especially.......

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The study was funded (awarded to F-Q.Z.) by NIH (R01NS064288, R01NS085176, R01GM111514, R01EY027347), the Craig H. Neilsen Foundation and the BrightFocus Foundation.


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Name Company Catalog Number Comments
ECM 830 Square wave electroporation system BTX Harvard Apparatus 45-0052 For in vivo electroporation
Tweezertrodes electrodes BTX Harvard Apparatus 45-0524 For in vivo electroporation, 1 mm flat
Picospritzer III Parker Instrumentation 1096 Intracellular Microinjection Dispense Systems
Glass Capillary Puller NARISHIGE PC-10
Borosilicate Glass Capillaries World Precision Instruments, Inc. 1902328
Stereo Dissection Microscope Leica M80
Microsurgery Rongeur F.S.T 16221-14
Microsurgery Forceps FST by DUMONT, Switzerland 11255-20 Only for sciatic nerve crush
Glass Capillary World Precision Instruments, Inc. TW100-4 10 cm, standard wall
Tape Fisherbrand 15-901-30 For fixing the mouse on the corkboard
2, 2, 2-Tribromoethanol (Avertin) Sigma-Aldrich T48402 Avertin stock solution
2-methyl-2-butanol Sigma-Aldrich 152463 Avertin stock solution
siRNA Fluorescent Universal Negative Control #1 Sigma-Aldrich SIC003 Non-target siRNA with fluorescence
microRNA Mimic Transfection Control with Dy547 Dharmacon CP-004500-01-05 Non-target microRNA with fluorescence
Plasmids preparation kit Invitrogen Purelink K210016 GFP-coding plasmid preparation
Fast Green Dye Millipore-Sigma F7252 For better visualization of the DRG outline during injection
Ketamine Putney, Inc NDC 26637-731-51 Anesthesia induction
Xylazine AnaSed NDC 59399-110-20 Anesthesia induction
Acetaminophen McNeil Consumer Healthcare NDC 50580-449-36 Post-surgical pain relief

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