This work was supported by NIH grant NS042197 to MD. AJK was supported by grants T32GM008719 and F30NS068006.

1. Production of Microinjection Needles
<ol>
 <li>Pre-fabricated microinjection needles are available commercially (e.g. Femtotips from Eppendorf) and are useful if one is not performing a large number of microinjections. However, for those who wish to establish long-term capabilities for microinjecting, an alternative is to produce microinjection needles in the lab using thin wall borosilicate glass capillaries and a commercial needle puller. This also allows the shape of needles to be varied, which can be useful for different cell types.</li>
 <li>With the Narishige PC-10 Microinjection Needle Puller, attach all four weights and use a one-step pulling program (Step 1 setting) with the relative heat setting at 58.0 (No.2 heater). Be sure to place the heating element at the center of each capillary so that the two resulting needles are a similar length.</li>
 <li>Pull several capillaries (about 2 capillaries for each protein of interest). </li>
 <li>Store needles in a container while being sure not to damage the needle tip. Materials such as foam or Blu-Tack can be used in containers to hold microinjection needles.</li> 
</ol>
2. Preparation of Protein Mixtures for Injection
<ol>
 <li>Prepare a 10x microinjection buffer containing 1 M potassium chloride and 0.1 M potassium phosphate (KPi) buffer (equimolar mixture of K2HPO4 and KH2PO4) at a pH of 7.4. This buffer can be stored long-term at room temperature.</li>
 <li>To visualize the injection, a fluorescent dye like rhodamine-dextran needs to be added. Dilute the10x microinjection buffer in water and dissolve rhodamine-dextran powder to make a 5x microinjection buffer solution containing 20-40 mg/mL rhodamine dextran.</li>
 <li>Store this solution in the dark at 4&deg;C. It should be sufficient for up to 100 individual protein solution preparations. Other dyes, like fluorescein isothiocyanate-dextran can substitute. </li>
 <li>Prepare cytochrome c stocks by dissolving purified cytochrome c in water to a concentration of 20 mg/mL. Store cytochrome c at -80&deg;C for long-term storage and avoid freeze-thaw cycles by storing cytochrome c in small (~10 &mu;L) aliquots.</li>
 <li>Prepare a 10 &mu;L protein mixture for injection by combining 2 &mu;L 5x microinjection buffer containing rhodamine-dextran with 3 &mu;L water and 5 &mu;L cytochrome c for a final concentration of 10 mg/mL cytochrome c in 1x buffer (100 mM KCl, 10 mM KPi, 4-8 mg/mL rhodamine dextran). </li>
</ol>

3. Cytoplasmic Microinjection of Cytochrome c
<ol>
 <li>Just prior to microinjection, centrifuge the mixture of cytochrome c and microinjection buffer at 16,000 g for 10 minutes at 4&deg;C to separate any particulate matter which may clog microinjection needles.</li>
 <li>During centrifugation, turn on the microinjector to allow air pressure to build.</li>
 <li>Place a dish of cells on the center of the microscope stage and set the focus on the cells. To minimize the amount of time that the cells are kept outside the incubator, cells are typically returned to the incubator within 30 min.</li>
 <li>Pipette 0.5-1 &mu;L from the top surface of the protein mixture into the blunt end of the capillary. Be careful to not pipette any particles which have been centrifuged to the bottom of the tube. Within a minute, the protein mixture will distribute to the needle tip through capillary action. </li>
 <li>Attach the needle firmly to the capillary holder of the micromanipulator and position the needle so that its tip passes through the transmitted light of the microscope at approximately a 45&deg; angle.</li>
 <li>Adjust the position of the needle tip so that it is located directly in the center of the field of view. To center the needle, use the micromanipulator to move the needle while looking through the microscope eyepiece. The needle shadow should be visible. Adjust the needle so that its shadow is only seen in one half of the field of view, indicating that the needle tip is centered above the cells.</li>
 <li>Set the microinjector to the Continuous Flow mode and set the working pressure to 20 - 100 hPa. Each needle may require a different working pressure, and the working pressure will likely need adjustment during the microinjection procedure to maintain a steady flow.</li>
 <li>Lower the needle using the coarse knob to a position just above the cells. To do this, raise the focal plane of the microscope to a position just above the cells. Then lower the needle towards the cells using the coarse knob until the needle tip is in focus.</li>
 <li>Re-center the needle tip within the field of view and increase magnification by changing the microscope objective.</li>
 <li>Slowly lower the needle using the fine manipulator knob until the needle is just slightly above the focal plane of the cells.</li>
 <li>Check the flow of the protein mixture by looking at the red fluorescence of the rhodamine. The protein mixture should be exiting the needle as a thin, constant stream. Needles should be replaced and re-loaded if the needle is compromised or if the flow is far too strong. Sometimes, the tip of the glass capillary is closed and no flow is seen from the needle. If this occurs, replace the needle or carefully lower it to the bottom of the culture dish to gently rupture the tip of the needle.</li>
 <li>Position the needle tip so that it is pointing towards a cell at approximately a 45&deg; angle. Then with one smooth motion, lower the needle while moving it towards the cell. With a second smooth motion, immediately reverse the direction of the needle to remove it from the cell.</li>
 <li>A successfully injected cell will often slightly swell and can be confirmed by visualizing the red fluorescent rhodamine within the cell. Occasionally, a cell will be accidentally injected in the nucleus, which will be visible.</li>
 <li>Continue to inject cells by adjusting the microscope stage until about 50-100 cells are injected. When moving the microscope stage, be sure to raise the microinjection needle so that it clears the top of cells.</li>
</ol>
4. Representative Results: 
The cytoplasmic microinjection of cytochrome c mimics its release from mitochondria during apoptosis. Thus, as expected, fibroblasts rapidly undergo apoptosis upon cytosolic microinjection of bovine cytochrome c (Fig. 1A). To ensure that the injection procedure alone is not responsible for cell death, injection of yeast cytochrome c serves as an important control, since yeast cytochrome c is incapable of activating caspases12.
Interestingly, post-mitotic sympathetic neurons are remarkably resistant to cytosolic cytochrome c (Fig. 1B)8,13. Our lab has identified that the endogenous caspase inhibitor XIAP is a key inhibitor of caspase activation in neurons14. Thus, for neurons to die following cytochrome c injection, XIAP must first become inactivated. For example, microinjection of cytochrome c into xiap-/- sympathetic neurons is sufficient to allow caspase activation and apoptosis in these cells (Fig. 2).
<img src="/files/ftp_upload/2773/2773fig1.jpg" alt="Figure 1"/> 
Figure 1. Cytoplasmic microinjection of cytochrome c induces rapid death in fibroblasts, but not neurons. A) Wild-type MEFs or (B) postnatal day 5 wild-type sympathetic neurons were microinjected with bovine cytochrome c (10 mg/mL) together with rhodamine-dextran to mark injected cells. Images show the same field of cells immediately following injection (0 hr), or at the indicated times. Arrows indicate injected cells. Scale bar, 20 &mu;m.
<img src="/files/ftp_upload/2773/2773fig2.jpg" alt="Figure 2"/> 
Figure 2. XIAP-deficient neurons are susceptible to cytoplasmic cytochrome c microinjection. Postnatal day 5 sympathetic neurons from XIAP knockout mice were microinjected with bovine cytochrome c (10 mg/mL) together with rhodamine-dextran to mark injected cells. Images show the same field of cells immediately following injection (0 hr), or 5 hours after cytochrome c microinjection (5 hr). Scale bar, 20 &mu;m.

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	<li>Danial, N. N., Korsmeyer, S. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+death:+critical+control+points.">Cell death: critical control points.</a> Cell. 116, 205-219 (2004).</li><li>Wang, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+expanding+role+of+mitochondria+in+apoptosis.">The expanding role of mitochondria in apoptosis.</a> Genes Dev. 15, 2922-2933 (2001).</li><li>Hengartner, M. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+biochemistry+of+apoptosis.">The biochemistry of apoptosis.</a> Nature. 407, 770-776 (2000).</li><li>Fuentes-Prior, P., Salvesen, G. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+protein+structures+that+shape+caspase+activity,+specificity,+activation+and+inhibition.">The protein structures that shape caspase activity, specificity, activation and inhibition.</a> Biochem. J. 384, 201-232 (2004).</li><li>Tait, S. W., Green, D. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mitochondria+and+cell+death:+outer+membrane+permeabilization+and+beyond.">Mitochondria and cell death: outer membrane permeabilization and beyond.</a> Nat Rev Mol Cell Biol. 11, 621-632 (2010).</li><li>Brustugun, O. T., Fladmark, K. E., Doskeland, S. O., Orrenius, S., Zhivotovsky, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Apoptosis+induced+by+microinjection+of+cytochrome+c+is+caspase-dependent+and+is+inhibited+by+Bcl-2.">Apoptosis induced by microinjection of cytochrome c is caspase-dependent and is inhibited by Bcl-2.</a> Cell Death Differ. 5, 660-668 (1998).</li><li>Li, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell-specific+induction+of+apoptosis+by+microinjection+of+cytochrome+c.+Bcl-XL+has+activity+independent+of+cytochrome+c+release.">Cell-specific induction of apoptosis by microinjection of cytochrome c. Bcl-XL has activity independent of cytochrome c release.</a> J. Biol. Chem. 272, 30299-30305 (1997).</li><li>Deshmukh, M., Johnson, E. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evidence+of+a+novel+event+during+neuronal+death:+development+of+competence-to-die+in+response+to+cytoplasmic+cytochrome+c.">Evidence of a novel event during neuronal death: development of competence-to-die in response to cytoplasmic cytochrome c.</a> Neuron. 21, 695-705 (1998).</li><li>Vaughn, A. E., Deshmukh, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Glucose+metabolism+inhibits+apoptosis+in+neurons+and+cancer+cells+by+redox+inactivation+of+cytochrome+c.">Glucose metabolism inhibits apoptosis in neurons and cancer cells by redox inactivation of cytochrome c.</a> Nat. Cell Biol. 10, 1477-1483 (2008).</li><li>Yang, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prevention+of+apoptosis+by+Bcl-2:+release+of+cytochrome+c+from+mitochondria+blocked.">Prevention of apoptosis by Bcl-2: release of cytochrome c from mitochondria blocked.</a> Science. 275, 1129-1132 (1997).</li><li>Gonzales, D. H., Neupert, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biogenesis+of+mitochondrial+c-type+cytochromes.">Biogenesis of mitochondrial c-type cytochromes.</a> J Bioenerg Biomembr. 22, 753-768 (1990).</li><li>Ellerby, 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=Establishment+of+a+cell-free+system+of+neuronal+apoptosis+-+comparison+of+premitochondrial,+mitochondrial,+and+postmitochondrial+phases.">Establishment of a cell-free system of neuronal apoptosis - comparison of premitochondrial, mitochondrial, and postmitochondrial phases.</a> J. Neurosci. 17, 6165-6178 (1997).</li><li>Neame, S. J., Rubin, L. L., Philpott, K. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Blocking+cytochrome+c+activity+within+intact+neurons+inhibits+apoptosis.">Blocking cytochrome c activity within intact neurons inhibits apoptosis.</a> J. Cell Biol. 142, 1583-1593 (1998).</li><li>Potts, P. R., Singh, S., Knezek, M., Thompson, C. 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All experimental procedures on animals were approved by the Institutional Animal Care and Use Committee at the University of North Carolina.

The microinjection of cytochrome c directly into the cytoplasm of cells is a unique and powerful tool which allows for studies of the post-mitochondrial regulation of apoptosis. Importantly, this technique allows for the direct activation of apoptosis downstream of mitochondria without the use of agents which cause cellular or mitochondrial damage. 
While this protocol has focused on microinjection of cytochrome c for studies on apoptosis, the general principles of protein ...

<table border="1">
	<tbody>
 <tr>
 	<th>Name of the reagent</th>
 <th>Company</th>
 <th>Catalogue number</th>
 <th>Comments</th>
 </tr>
 <tr>
 	<td>DM IRE2 Inverted Microscope</td>
 <td>Leica</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 	<td>PC-10 Microinjection Needle Puller</td>
 <td>Narishige</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 	<td>MWO-202 Micromanipulator</td>
 <td>Narishige</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 	<td>FemtoJet Microinjector</td>
 <td>Eppendorf</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 	<td>Thin-wall Boroscilicate Capillary Glass with Microfilament</td>
 <td>A-M Systems</td>
 <td>615000</td>
 <td>4 inch length, 1.00 mm outer diameter, 0.75 mm inner diameter</td>
 </tr>
 <tr>
 	<td>Rhodamine B isothiocyanate-Dextran</td>
 <td>Sigma-Aldrich</td>
 <td>R9379</td>
 <td>Average molecular weight ~70,000 Da</td>
 </tr>
 <tr>
 	<td>Bovine Cytochrome c Protein</td>
 <td>Sigma-Aldrich</td>
 <td>C3131</td>
 <td>&nbsp;</td>
 </tr>
 
 </tbody>
</table>

activation of apoptosis by cytoplasmic microinjection of cytochrome c

Apoptosis, or programmed cell death, is a conserved and highly regulated pathway by which cells die1. Apoptosis can be triggered when cells encounter a wide range of cytotoxic stresses. These insults initiate signaling cascades that ultimately cause the release of cytochrome c from the mitochondrial intermembrane space to the cytoplasm2. The release of cytochrome c from mitochondria is a key event that triggers the rapid activation of caspases, the key cellular proteases which ultimately execute cell death3-4.
The pathway of apoptosis is regulated at points upstream and downstream of cytochrome c release from mitochondria5. In order to study the post-mitochondrial regulation of caspase activation, many investigators have turned to direct cytoplasmic microinjection of holocytochrome c (heme-attached) protein into cells6-9. Cytochrome c is normally localized to the mitochondria where attachment of a heme group is necessary to enable it to activate apoptosis10-11. Therefore, to directly activate caspases, it is necessary to inject the holocytochrome c protein instead of its cDNA, because while the expression of cytochrome c from cDNA constructs will result in mitochondrial targeting and heme attachment, it will be sequestered from cytosolic caspases. Thus, the direct cytosolic microinjection of purified heme-attached cytochrome c protein is a useful tool to mimic mitochondrial cytochrome c release and apoptosis without the use of toxic insults which cause cellular and mitochondrial damage.
In this article, we describe a method for the microinjection of cytochrome c protein into cells, using mouse embryonic fibroblasts (MEFs) and primary sympathetic neurons as examples. While this protocol focuses on the injection of cytochrome c for investigations of apoptosis, the techniques shown here can also be easily adapted for microinjection of other proteins of interest.

Watch this Scientific Journal Video about Activation of Apoptosis by Cytoplasmic Microinjection of Cytochrome c at JoVE.com

Activation of Apoptosis by Cytoplasmic Microinjection of Cytochrome c

In this protocol, we describe the direct cytoplasmic microinjection of cytochrome c protein into fibroblasts and primary sympathetic neurons. This technique allows for the introduction of cytochrome c protein into the cytoplasm of cells and mimics the release of cytochrome c from mitochondria, which occurs during apoptosis.

Activation of Apoptosis by Cytoplasmic Microinjection of Cytochrome c

Apoptosis, or programmed cell death, is a conserved and highly regulated pathway by which cells die1.  Apoptosis can be triggered when cells encounter a ...

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17.3K Views.  University of North Carolina. In this protocol, we describe the direct cytoplasmic microinjection of cytochrome c protein into fibroblasts and primary sympathetic neurons. This technique allows for the introduction of cytochrome c protein into the cytoplasm of cells and mimics the release of cytochrome c from mitochondria, which occurs during apoptosis.

Video: Activation of Apoptosis by Cytoplasmic Microinjection of Cytochrome c

Interview: Glycolipid Antigen Presentation by CD1d and the Therapeutic Potential of NKT cell Activation

Natural Killer T cells (NKT) are critical determinants of the immune response to cancer, regulation of autioimmune disease, clearance of infectious agents, and the development of artheriosclerotic plaques.   In this interview, Mitch Kronenberg discusses his laboratory's efforts to understand the mechanism through which NKT cells are activated by glycolipid antigens.  Central to these studies is CD1d - the antigen presenting molecule that presents glycolipids to NKT cells.  The advent of CD1d tetramer technology, a technique developed by the Kronenberg lab, is critical for the sorting and identification of subsets of specific glycolipid-reactive T cells.  Mitch explains how glycolipid agonists are being used as therapeutic agents to activate NKT cells in cancer patients and how CD1d tetramers can be used to assess the state of the NKT cell population in vivo following glycolipid agonist therapy.  Current status of ongoing clinical trials using these agonists are discussed as well as Mitch's prediction for areas in the field of immunology that will have emerging importance in the near future.

Natural Killer T cells (NKT) are critical determinants of the immune response to cancer, regulation of autioimmunity, clearance of infection, and the development of artheriosclerotic plaques. In this interview, Mitch Kronenberg discusses his laboratory's efforts to understand the mechanism through which NKT cells are activated by glycolipid antigens.

Natural Killer T cells (NKT) are critical determinants of the immune response to cancer, regulation of autioimmune disease, clearance of infectious ...

Generation of Stable Transgenic C. elegans Using Microinjection

Transgenic Caenorhabditis elegans can be readily created via microinjection of a DNA plasmid solution into the gonad 1. The plasmid DNA rearranges to form extrachromosomal concatamers that are stably inherited, though not with the same efficiency as actual chromosomes 2. A gene of interest is co-injected with an obvious phenotypic marker, such as rol-6 or GFP, to allow selection of transgenic animals under a dissecting microscope. The exogenous gene may be expressed from its native promoter for cellular localization studies. Alternatively, the transgene can be driven by a different tissue-specific promoter to assess the role of the gene product in that particular cell or tissue. This technique efficiently drives gene expression in all tissues of C. elegans except for the germline or early embryo 3. Creation of transgenic animals is widely utilized for a range of experimental paradigms. This video demonstrates the microinjection procedure to generate transgenic worms. Furthermore, selection and maintenance of stable transgenic C. elegans lines is described.

This video demonstrates the technique of microinjection into the gonad of C. elegans to create transgenic animals.

Transgenic Caenorhabditis elegans can be readily created via microinjection of a DNA plasmid solution into the gonad 1.  The plasmid DNA rearranges to ...

Microinjection of Xenopus Laevis Oocytes

Microinjection of Xenopus laevis oocytes followed by thin-sectioning electron microscopy (EM) is an excellent system for studying nucleocytoplasmic transport. Because of its large nucleus and high density of nuclear pore complexes (NPCs), nuclear transport can be easily visualized in the Xenopus oocyte. Much insight into the mechanisms of nuclear import and export has been gained through use of this system (reviewed by Pant&eacute;, 2006). In addition, we have used microinjection of Xenopus oocytes to dissect the nuclear import pathways of several viruses that replicate in the host nucleus. 
Here we demonstrate the cytoplasmic microinjection of Xenopus oocytes with a nuclear import substrate. We also show preparation of the injected oocytes for visualization by thin-sectioning EM, including dissection, dehydration, and embedding of the oocytes into an epoxy embedding resin. Finally, we provide representative results for oocytes that have been microinjected with the capsid of the baculovirus Autographa californica nucleopolyhedrovirus (AcMNPV) or the parvovirus Minute Virus of Mice (MVM), and discuss potential applications of the technique.

Here we demonstrate cytoplasmic microinjection of Xenopus laevis oocytes with a nuclear import substrate, as well as preparation of the injected oocytes for visualization by thin-sectioning electron microscopy.

Microinjection of Xenopus laevis oocytes followed by thin-sectioning electron microscopy (EM) is an excellent system for studying nucleocytoplasmic ...

Generation of Transgenic C. elegans by Biolistic Transformation

The number of laboratories using the free living nematode C. elegans is rapidly growing. The popularity of this biological model is attributed to a rapid generation time and short life span, easy and inexpensive maintenance, fully sequenced genome, and array of RNAi resources and mutant animals. Additionally, analysis of the C. elegans genome revealed a great similarity between worms and higher vertebrates, which suggests that research in worms could be an important adjunct to studies performed in whole mice or cultured cells. A powerful and important part of worm research is the ability to use transgenic animals to study gene localization and function. Transgenic animals can be created either via microinjection of the worm germline or through the use of biolistic bombardment. Bombardment is a newer technique and is less familiar to a number of labs. Here we describe a simple protocol to generate transgenic worms by biolistic bombardment with gold particles using the Bio-Rad PDS-1000 system. Compared with DNA microinjection into hermaphrodite germline, this protocol has the advantage of not requiring special skills from the operator with regards to identifying worm anatomy or performing microinjection. Further multiple transgenic lines are usually obtained from a single bombardment. Also in contrast to microinjection, biolistic bombardment produces transgenic animals with both extrachromosomal arrays and integrated transgenes. The ability to obtain integrated transgenic lines can avoid the use of mutagenic protocols to integrate foreign DNA. In conclusion, biolistic bombardment can be an attractive method for the generation of transgenic animals, especially for investigators not interested in investing the time and effort needed to become skilled at microinjection.

Generation of Transgenic C. elegans by Biolistic Transformation

Transgenic worms are commonly used in C. elegans research. Described is a simple, yet effective, protocol to introduce transgenes into worms using biolistic bombardment with DNA-coated gold particles. The effort involved and results of bombardment compare favorably with microinjection for the generation of transgenic animals.

The number of laboratories using the free living nematode C. elegans is rapidly growing. The popularity of this biological model is attributed to a rapid ...

Analysis of mRNA Nuclear Export Kinetics in Mammalian Cells by Microinjection

In eukaryotes, messenger RNA (mRNA) is transcribed in the nucleus and must be exported into the cytoplasm to access the translation machinery. Although the nuclear export of mRNA has been studied extensively in Xenopus oocytes1 and genetically tractable organisms such as yeast2 and the Drosophila derived S2 cell line3, few studies had been conducted in mammalian cells. Furthermore the kinetics of mRNA export in mammalian somatic cells could only be inferred indirectly4,5. In order to measure the nuclear export kinetics of mRNA in mammalian tissue culture cells, we have developed an assay that employs the power of microinjection coupled with fluorescent in situ hybridization (FISH). These assays have been used to demonstrate that in mammalian cells, the majority of mRNAs are exported in a splicing dependent manner6,7, or in manner that requires specific RNA sequences such as the signal sequence coding region (SSCR) 6. In this assay, cells are microinjected with either in vitro synthesized mRNA or plasmid DNA containing the gene of interest. The microinjected cells are incubated for various time points then fixed and the sub-cellular localization of RNA is assessed using FISH. In contrast to transfection, where transcription occurs several hours after the addition of nucleic acids, microinjection of DNA or mRNA allows for rapid expression and allows for the generation of precise kinetic data.

Here we describe an assay that employs the power of microinjection coupled with fluorescent in situ hybridization in order to accurately measure the nuclear export kinetics of mRNA in mammalian somatic cells.

In eukaryotes, messenger RNA (mRNA) is transcribed in the nucleus and must be exported into the cytoplasm to access the translation machinery. Although ...

Analyzing the Function of Small GTPases by Microinjection of Plasmids into Polarized Epithelial Cells

Epithelial cells polarize their plasma membrane into biochemically and functionally distinct apical and basolateral domains where the apical domain faces the 'free' surfaces and the basolateral membrane is in contact with the substrate and neighboring cells. Both membrane domains are separated by tight junctions, which form a diffusion barrier. Apical-basolateral polarization can be recapitulated successfully in culture when epithelial cells such as Madin-Darby Canine Kidney (MDCK) cells are seeded at high density on polycarbonate filters and cultured for several days 1 2. Establishment and maintenance of cell polarity is regulated by an array of small GTPases of the Ras superfamily such as RalA, Cdc42, Rab8, Rab10 and Rab13 3 4 5 6 7. Like all GTPases these proteins cycle between an inactive GDP-bound state and an active GTP-bound state. Specific mutations in the nucleotide binding regions interfere with this cycling 8. For example, Rab13T22N is permanently locked in the GDP-form and thus dubbed 'dominant negative', whereas Rab13Q67L can no longer hydrolyze GTP and is thus locked in a 'dominant active' state 7. To analyze their function in cells both dominant negative and dominant active alleles of GTPases are typically expressed at high levels to interfere with the function of the endogenous proteins 9. An elegant way to achieve high levels of overexpression in a short amount of time is to introduce the plasmids encoding the relevant proteins directly into the nuclei of polarized cells grown on filter supports using microinjection technique. This is often combined with the co-injection of reporter plasmids that encode plasma membrane receptors that are specifically sorted to the apical or basolateral domain. A cargo frequently used to analyze cargo sorting to the basolateral domain is a temperature sensitive allele of the vesicular stomatitis virus glycoprotein (VSVGts045) 10. This protein cannot fold properly at 39&deg;C and will thus be retained in the endoplasmic reticulum (ER) while the regulatory protein of interest is assembled in the cytosol. A shift to 31&deg;C will then allow VSVGts045 to fold properly, leave the ER and travel to the plasma membrane 11. This chase is typically performed in the presence of cycloheximide to prevent further protein synthesis leading to cleaner results. Here we describe in detail the procedure of microinjecting plasmids into polarized cells and subsequent incubations including temperature shifts that allow a comprehensive analysis of regulatory proteins involved in basolateral sorting.

This article details the procedures involved in overexpression and analysis of small GTPases in polarized epithelial cells using microinjection technique.

Epithelial cells polarize their plasma membrane into biochemically and functionally distinct apical and basolateral domains where the apical domain faces ...

Visualization of Mitochondrial Respiratory Function using Cytochrome C Oxidase / Succinate Dehydrogenase (COX/SDH) Double-labeling Histochemistry

Mitochondrial DNA (mtDNA) defects are an important cause of disease and may underlie aging and aging-related alterations 1,2. The mitochondrial theory of aging suggests a role for mtDNA mutations, which can alter bioenergetics homeostasis and cellular function, in the aging process 3. A wealth of evidence has been compiled in support of this theory 1,4, an example being the mtDNA mutator mouse 5; however, the precise role of mtDNA damage in aging is not entirely understood 6,7.
Observing the activity of respiratory enzymes is a straightforward approach for investigating mitochondrial dysfunction. Complex IV, or cytochrome c oxidase (COX), is essential for mitochondrial function. The catalytic subunits of COX are encoded by mtDNA and are essential for assembly of the complex (Figure 1). Thus, proper synthesis and function are largely based on mtDNA integrity 2. Although other respiratory complexes could be investigated, Complexes IV and II are the most amenable to histochemical examination 8,9. Complex II, or succinate dehydrogenase (SDH), is entirely encoded by nuclear DNA (Figure 1), and its activity is typically not affected by impaired mtDNA, although an increase might indicate mitochondrial biogenesis 10-12. The impaired mtDNA observed in mitochondrial diseases, aging, and age-related diseases often leads to the presence of cells with low or absent COX activity 2,12-14. Although COX and SDH activities can be investigated individually, the sequential double-labeling method 15,16 has proved to be advantageous in locating cells with mitochondrial dysfunction 12,17-21.
Many of the optimal constitutions of the assay have been determined, such as substrate concentration, electron acceptors/donors, intermediate electron carriers, influence of pH, and reaction time 9,22,23. 3,3'-diaminobenzidine (DAB) is an effective and reliable electron donor 22. In cells with functioning COX, the brown indamine polymer product will localize in mitochondrial cristae and saturate cells 22. Those cells with dysfunctional COX will therefore not be saturated by the DAB product, allowing for the visualization of SDH activity by reduction of nitroblue tetrazolium (NBT), an electron acceptor, to a blue formazan end product 9,24. Cytochrome c and sodium succinate substrates are added to normalize endogenous levels between control and diseased/mutant tissues 9. Catalase is added as a precaution to avoid possible contaminating reactions from peroxidase activity 9,22. Phenazine methosulfate (PMS), an intermediate electron carrier, is used in conjunction with sodium azide, a respiratory chain inhibitor, to increase the formation of the final reaction products 9,25. Despite this information, some critical details affecting the result of this seemly straightforward assay, in addition to specificity controls and advances in the technique, have not yet been presented.

Visualization of Mitochondrial Respiratory Function using Cytochrome C Oxidase / Succinate Dehydrogenase COX/SDH Double-labeling Histochemistry

The cytochrome c oxidase/sodium dehydrogenase (COX/SDH) double-labeling method allows for direct visualization of mitochondrial respiratory enzyme deficiencies in fresh-frozen tissue sections. This is a straightforward histochemical technique and is useful in investigating mitochondrial diseases, aging, and aging-related disorders.

Mitochondrial DNA (mtDNA) defects are an important cause of disease and may underlie aging and aging-related alterations 1,2. The mitochondrial theory of ...

Synthesis of an In vivo MRI-detectable Apoptosis Probe

Cellular apoptosis is a prominent feature of many diseases, and this programmed cell death typically occurs before clinical manifestations of disease are evident. A means to detect apoptosis in its earliest, reversible stages would afford a pre-clinical 'window' during which preventive or therapeutic measures could be taken to protect the heart from permanent damage. We present herein a simple and robust method to conjugate human Annexin V (ANX), which avidly binds to cells in the earliest, reversible stages of apoptosis, to superparamagnetic iron oxide (SPIO) nanoparticles, which serve as an MRI-detectable contrast agent. The conjugation method begins with an oxidation of the SPIO nanoparticles, which oxidizes carboxyl groups on the polysaccharide shell of SPIO. Purified ANX protein is then added in the setting of a sodium borate solution to facilitate covalent interaction of ANX with SPIO in a reducing buffer. A final reduction step with sodium borohydride is performed to complete the reduction, and then the reaction is quenched. Unconjugated ANX is removed from the mix by microcentrifuge filtration. The size and purity of the ANX-SPIO product is verified by dynamic light scattering (DLS). This method does not require addition to, or modification of, the polysaccharide SPIO shell, as opposed to cross-linked iron oxide particle conjugation methods or biotin-labeled nanoparticles. As a result, this method represents a simple, robust approach that may be extended to conjugation of other proteins of interest.

Synthesis of an In vivo MRI-detectable Apoptosis Probe

Early detection of apoptosis may identify at-risk cell populations in a variety of diseases. Here we demonstrate a method to link an early apoptosis-detection protein (Annexin V) to a MRI-detectable iron oxide nanoparticle (SPIO). This method may be extended to other proteins of interest to generate MRI-detectable molecular imaging probes.

Cellular apoptosis is a prominent feature of many diseases, and this programmed cell death typically occurs before clinical manifestations of disease are ...

Single-molecule Imaging of Gene Regulation In vivo Using Cotranslational Activation by Cleavage (CoTrAC)

We describe a fluorescence microscopy method, Co-Translational Activation by Cleavage (CoTrAC) to image the production of protein molecules in live cells with single-molecule precision without perturbing the protein's functionality. This method makes it possible to count the numbers of protein molecules produced in one cell during sequential, five-minute time windows. It requires a fluorescence microscope with laser excitation power density of ~0.5 to 1 kW/cm2, which is sufficiently sensitive to detect single fluorescent protein molecules in live cells. The fluorescent reporter used in this method consists of three parts: a membrane targeting sequence, a fast-maturing, yellow fluorescent protein and a protease recognition sequence. The reporter is translationally fused to the N-terminus of a protein of interest. Cells are grown on a temperature-controlled microscope stage. Every five minutes, fluorescent molecules within cells are imaged (and later counted by analyzing fluorescence images) and subsequently photobleached so that only newly translated proteins are counted in the next measurement.
Fluorescence images resulting from this method can be analyzed by detecting fluorescent spots in each image, assigning them to individual cells and then assigning cells to cell lineages. The number of proteins produced within a time window in a given cell is calculated by dividing the integrated fluorescence intensity of spots by the average intensity of single fluorescent molecules. We used this method to measure expression levels in the range of 0-45 molecules in single 5 min time windows. This method enabled us to measure noise in the expression of the &lambda; repressor CI, and has many other potential applications in systems biology.

Single-molecule Imaging of Gene Regulation In vivo Using Cotranslational Activation by Cleavage CoTrAC

We describe a fluorescence microscopy method, Co-Translational Activation by Cleavage (CoTrAC), to image the production of protein molecules in live cells with single-molecule precision without perturbing the protein's functionality. This method has been used to follow the stochastic expression dynamics of a transcription factor, the &lambda; repressor CI 1.

We describe a fluorescence microscopy method, Co-Translational Activation by Cleavage (CoTrAC) to image the production of protein molecules in live cells ...

Analysis of Apoptosis in Zebrafish Embryos by Whole-mount Immunofluorescence to Detect Activated Caspase 3

Whole-mount immunofluorescence to detect activated Caspase 3 (Casp3 assay) is useful to identify cells undergoing either intrinsic or extrinsic apoptosis in zebrafish embryos. The whole-mount analysis provides spatial information in regard to tissue specificity of apoptosing cells, although sectioning and/or colabeling is ultimately required to pinpoint the exact cell types undergoing apoptosis. The whole-mount Casp3 assay is optimized for analysis of fixed embryos between the 4-cell stage and 32 hr-post-fertilization and is useful for a number of applications, including analysis of zebrafish mutants and morphants, overexpression of mutant and wild-type mRNAs, and exposure to chemicals. Compared to acridine orange staining, which can identify apoptotic cells in live embryos in a matter of hours, Casp3 and TUNEL assays take considerably longer to complete (2-4 days). However, because of the dynamic nature of apoptotic cell formation and clearance, analysis of fixed embryos ensures accurate comparison of apoptotic cells across multiple samples at specific time points. We have also found the Casp3 assay to be superior to analysis of apoptotic cells by the whole-mount TUNEL assay in regard to cost and reliability. Overall, the Casp3 assay represents a robust, highly reproducible assay in which to analyze apoptotic cells in early zebrafish embryos.

Certain genetic perturbations or exposure to toxins can disrupt normal developmental processes leading to death of specific cell types. The analysis of activated Caspase 3 by whole-mount immunofluorescence in zebrafish embryos reveals stage- and tissue-specific localization of cells specifically undergoing apoptosis.

Whole-mount immunofluorescence to detect activated Caspase 3 (Casp3 assay) is useful to identify cells undergoing either intrinsic or extrinsic apoptosis ...