This research was supported by the Intramural Research Program of the National Institute of Health (NIH), National Institute of Environmental Health Sciences (NIEHS). We are grateful to Dr. Robert Petrovich and Dr. Jason Williams for critical reading of the manuscript and helpful advice. We would also like to acknowledge and thank Dr. Bernd Gloss, the Knockout core, the Flow Cytometry Facility, the Fluorescence Microscopy and Imaging Center, and the Comparative Medicine Branch facilities of the NIEHS for their technical contributions. We would like to thank Mr. David Goulding from the Comparative Medicine Branch and Ms. Lois Wyrick of the Imaging Center at the NIEHS for providing us with photographs and illustrations.

All animal procedures and treatments used in this protocol were in compliance with the NIH/NIEHS animal care guidelines and were approved by the Animal Care and Use Committee (ACUC) at the NIH/NIEHS, Animal Protocol 2010-0004.
1. Preparations
<ol>
	<li>Prepare/purchase recombinant non-propagating lentiviruses carrying your gene of interest. In this study, lentivirus SBI511 expressing copepod green fluorescent protein (copGFP; abbreviated to GFP) from an elongation factor 1a promoter was used for transduction. Standard protocols2 were used to produce and titer lentiviruses at titers higher than 1e8 transducing units per mL (TU/mL). 
	NOTE: Use caution and bleach all material that have been in contact with lentiviruses. Refer to your institute&#39;s guidelines for safe use and handling of lentiviruses.</li>
	<li>Setup breeding pairs of desired mouse strain the day before harvesting embryos. In this experiment, C57BL/6J strain of mice was used. Female mice used for ovaries and oviduct collection were not treated with any hormones for superovulation.</li>
	<li>2&#8211;24 h prior to harvesting mouse fertilized eggs, prepare several Potassium Simplex Optimized Medium24 (KSOM) drop plates as follows: add a 50 &#956;L drop of KSOM medium to the middle of a 35 mm tissue culture-treated dish and cover with 2 mL of Dimethylpolysiloxane (DMPS5X) and place at 37 oC, 5% CO2, 5% O2 and 90% N2 to equilibrate. 
	NOTE: Use disposable sterile plates and discard following exposure to lentiviruses.</li>
	<li>Prepare 1x solution of hyaluronidase in M2 medium from stock solution (100x, 30 mg/mL, store at -20 &#176;C). 100x stock solution was prepared in water.</li>
	<li>24 h post laser-assisted transduction of mouse fertilized eggs, set up breeding pairs between vasectomized male and female mice to prepare pseudopregnant female mice.</li>
</ol>
2. Isolation of Mouse Fertilized Eggs
<ol>
	<li>16&#8211;24 h post mating, select female mice with vaginal plugs indicative of successful mating and humanely euthanize25. The mice used in this study were euthanized by cervical dislocation under deep CO2 or isoflurane inhalation.</li>
	<li>Isolate ovaries and oviducts according to standard protocols25.</li>
	<li>Transfer the ovaries and oviducts to a 35 mm dish containing M2 media.</li>
	<li>For each ovary, tear ampulla apart to release fertilized eggs surrounded by cumulus cells.</li>
	<li>Transfer fertilized eggs and cumulus cells to a 35 mm dish containing 1x hyaluronidase in M2 medium and incubate at room temperature for 3&#8211;5 min.</li>
	<li>Pipet fertilized eggs up and down to release the cumulus cells.</li>
	<li>Transfer fertilized eggs to a 35 mm dish containing M2 media and pipet up and down to wash off hyaluronidase.</li>
	<li>Transfer fertilized eggs to a 35 mm dish containing KSOM and pipet up and down to wash off the remaining M2 media and hyaluronidase.</li>
	<li>Transfer fertilized eggs to the prepared KSOM drop plates from step 1.3. 
	NOTE: Mouse fertilized eggs in KSOM must be kept in a tissue culture incubator at 37 &#176;C, 5% CO2, 5% O2 and 90% N2 to equilibrate. Removing plates from the incubator for longer than 15 min will result in damage to embryos.</li>
	<li>Allow fertilized eggs to recover for 2 h in the incubator before moving to the next step.</li>
</ol>
3. Perforation of Mouse Fertilized Eggs with XYClone Laser
<ol>
	<li>Setup and calibrate XYClone laser according to the manufacturer&#39;s recommendation. Other lasers, typically used for in vitro fertilization, can be substituted for XYClone laser to perforate fertilized eggs.
	<ol>
		<li>Attach the laser controller box wire to the laser apparatus on the microscope.</li>
		<li>Attach the laser controller box to the computer running the laser software via a USB port. 3.1.3. Plug in the laser controller and switch it on.</li>
		<li>Looking through the eyepiece, perforate a test sample (e.g. dry-erase markings on a glass slide).</li>
		<li>Use a small screw driver (included in the laser kit) to adjust the X and Y position of the laser to match the LED light visible through the microscope eyepiece and calibrate the laser.</li>
	</ol>
	</li>
	<li>Place a KSOM drop plate containing mouse fertilized eggs on the microscope stage. Do not keep the plate outside of the incubator for longer than 15 min.</li>
	<li>Look through the microscope eyepiece and ensure that the embryo&#39;s zona pellucida is in focus and the laser LED light is visible.</li>
	<li>Move the microscope stage to target the zona with the LED light/laser.</li>
	<li>Using the computer software set XYClone laser to 250 &#956;s.</li>
	<li>Adjust the LED light size to desired dimensions (setting 5 in this experiment).</li>
	<li>Perforate the zona of each fertilized egg thrice with the laser. The zona can be either pierced or thinned. Using the above settings, the laser will produce a hole with a diameter of 10 &#956;m (Figure 2). 
	NOTE: Aiming close to the polar body keeps laser away from the embryonic cell.</li>
	<li>Allow fertilized eggs to recover for 2 h in the tissue culture incubator before moving to the next step.</li>
</ol>
4. Transduction of Mouse Fertilized Eggs Following XYClone Laser Perforation
<ol>
	<li>Pipet 2 &#956;L of concentrated lentivirus (greater than 1e8 TU/mL titer) into the 50 &#956;L KSOM drop. Do not pipet up and down. Fertilized eggs readily attach to the pipet tip. Based on our experience, 1e5-5e5 transducing units of lentivirus in a volume less than 3 &#956;L is optimal for gene delivery.</li>
	<li>Allow fertilized eggs to develop into blastocyst for 4 days in the incubator. No need to change the media.</li>
</ol>
5. Non-surgical Transfer of Transduced Mouse Embryos to Pseudo-pregnant Mice
<ol>
	<li>Use pseudopregnant mice, 3.5 day after mating, prepared in step 1.5.</li>
	<li>Use Non-Surgical Embryo Transfer (NSET) device to implant mouse embryos into pseudopregnant mice.
	<ol>
		<li>Using a surgical or dissecting microscope, insert a vaginal speculum to visualize the cervix.</li>
		<li>Insert the Non-Surgical Embryo Transfer (NSET) device approximately 5 mm into the cervix and deposit embryos in a volume of approximately 2 &#956;L. 
		NOTE: A sterile NSET device is used for each transfer and discarded after the procedure. All reagents used in the manipulation of the embryos must be sterile.</li>
	</ol>
	</li>
	<li>Transfer 10&#8211;15 healthy blastocyst in 2 &#956;L volume of KSOM to each pseudopregnant mice.</li>
	<li>Continue to monitor and measure the weight gain in pseudopregnant mice in following days to determine whether the NSET was successful.</li>
	<li>Recover pups by allowing the pregnant mice to give birth naturally or performing a caesarean section 17 days after the embryo transfer26. A C-section is often necessary if very few embryos are present and they grow too large for natural birth.</li>
	<li>Collect tissue from pups for genotyping to determine the rate of transgenesis27.</li>
</ol>

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E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laser-assisted+in+vitro+fertilization+facilitates+fertilization+of+vitrified-warmed+C57BL/6+mouse+oocytes+with+fresh+and+frozen-thawed+spermatozoa,+producing+live+pups.">Laser-assisted in vitro fertilization facilitates fertilization of vitrified-warmed C57BL/6 mouse oocytes with fresh and frozen-thawed spermatozoa, producing live pups.</a> PLoS One. 9 (3), e91892 (2014).</li><li>Tanaka, N., Takeuchi, T., Neri, Q. V., Sills, E. S., Palermo, G. 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The authors have nothing to disclose.

The ability of the lentiviruses to integrate into their host genome makes them an ideal vector for stable gene delivery. Lentiviral vectors can carry up to 8.5 kilobase pair (kbp) of genetic material that can accommodate cell-specific or inducible promoters, selection markers, or fluorescent moieties. Incorporated genomic material can replicate as part of their host genome and be regulated to express or deactivate at desired time points. These vectors allow for spatiotemporal control over gene expression at various stages of development and brand lentiviruses as powerful tools for gene delivery.
Laser-assisted lentiviral transgenesis is an effective and easy-to-use method for gene expression in vivo. This method can be used for in vivo protein production, expression of genetically encoded indicators, or functional studies. Compared to other methods, laser-assisted lentiviral gene delivery is as effective as pronuclear microinjection but requires no technical skills or costly microinjection workstations. The XYClone laser is small, portable, and can easily be shared among several laboratories.
Laser-assisted lentiviral gene delivery is stable and not transient, as in electroporation or photoporation of fertilized eggs. Transient gene delivery is more advantages for delivery of CRISPR-Cas9 components or recombinases since extended expression could lead to aberrant consequences. In this protocol, the integrase deficient lentiviruses (IDLVs) can be substituted for transient transduction of mouse fertilized eggs. IDLVs retain lentiviral infectivity but only retain a fraction (less than 8%) of integrative capability of lentiviruses29. Laser-assisted lentiviral transgenesis is an additional gene delivery option for users to evaluate based on their desired outcome.
The major disadvantage of lentiviral transduction is the random insertion of the delivered gene. Also, cells within the same embryo could host multiple lentiviral integrations that leads to mosaicism in the transgenic. Genotyping of the progeny and multiple rounds of planned breeding is necessary to establish a single locus transgenic animal. Similar breeding strategies are also employed in conventional transgenesis methods30.
A critical step in this protocol is the length of time spent on laser perforation. Mouse fertilized eggs cultured in KSOM cannot be kept outside of the incubator for longer than 15 min. A novice user should move the fertilized eggs to M2 medium, use Advanced KSOM Embryo Medium, or limit the number of embryos per plate. According to our result, 47% of transduced cultured mouse fertilized eggs develop into blastocysts23. Therefore, culturing 30-40 fertilized eggs per plate will ensure adequate number of transduced blastocysts in one plate for transfer into pseudopregnant mice.
Laser-assisted perforation of the mouse fertilized egg zona may also be applicable to the zona of other species and allow entry for other types of viruses or transfection reagents.

This method provides detailed instructions for permeabilizing the zona pellucida of mouse fertilized eggs to make embryonic cells accessible for gene delivery by lentiviruses. Lentiviruses are designed by nature for efficient gene delivery to mammalian cells. They infect dividing and non-dividing cells and integrate the lentiviral genome into their host chromosomes1. The range of lentiviral host cells is readily expanded by pseudotyping the recombinant lentivirus with the vesicular stomatitis virus glycoprotein (VSV-G), due to the broad tropism of the VSV-G protein2. Following transduction, lentiviral genes are stably integrated and expressed as part of their host chromosomes creating an ideal tool for generating transgenic animals. If delivered to early stage embryonic cells, the lentiviral genome is replicated and expressed in the entire organism. Lentiviral transduction has led to the production of mice, rat, chicken, quail and pig3,4,5,6,7 among other species of transgenics. The typical method of lentiviral gene delivery, however, requires skilled technicians and specialized equipment to overcome the zona pellucida barrier that encapsulates the early stage embryos. The overall goal of this method is to describe how to permeabilize the zona using a laser to facilitate lentiviral gene delivery.
Mammalian eggs are surrounded by the zona pellucida which hardens following fertilization to protect the fertilized eggs against polyspermy and to limit environmental interactions8,9. The zona forms a barrier that keeps lentiviruses away from the embryonic cells until the embryos are hatched as a blastocyst. Cultured mouse fertilized eggs hatch after 4 days and must be implanted into pseudopregnant mice prior to hatching for normal development into pups. Therefore, for transduction, lentiviruses are microinjected before hatching from the zona into the perivitelline cavity, the space between the zona and the embryonic cells.
The zona pellucida is often removed for in vitro fertilization of human eggs to increase the fertilization rate10. However, chemical removal of mouse zona pellucida adversely affects mouse embryo development and is harmful to embryonic cells11,12. Other methods for gene delivery to mouse fertilized eggs overcome the zona pellucida barrier by direct microinjection of DNA into the cell nucleus13. Pronuclear microinjection is an efficient means of delivering genes to embryos. However, since each embryo is held in place individually for microinjection, the practice can be laborious and time consuming for a novice user.
Other methods such as electroporation and photoporation are useful for transient and short-term gene delivery to mouse fertilized eggs14,15,16. These methods are extensively used for delivering CRISPR-Cas9 components and recombinases. However, electroporation and photoporation delivery of genes cannot be used efficiently to create transgenics. Spermatozoa that are collected from punctured mouse epididymis can also be transduced by lentiviruses and used for in vitro fertilization to produce transgenic animals17,18,19,20.
In this protocol, the lentiviral gene delivery to mouse embryos is facilitated by permeabilizing the zona using a laser. The XYClone laser was developed as an aid for in vitro fertilization21 and cultivation of embryonic stem cells22. It is a small apparatus that is simple to setup and easy to use. Once installed on a microscope, it occupies the space of an objective lens and the accompanying software allows for aiming the laser while looking through the microscope eyepieces (see Protocol: section 3). Once the zona is perforated by the XYClone laser, lentiviruses can be introduced into the culture media for gene delivery23. Multiple lentiviruses could be used to simultaneously deliver several genes for chromosomal incorporation.
This protocol will describe how to isolate and culture mouse fertilized eggs, illustrates the use of laser for perforation of the zona pellucida, and demonstrates the transduction of mouse embryonic cells by lentiviruses.

<table>
	<tbody>
		<tr>
			<td>CD510B-1 plasmid</td>
			<td>System Biosciences</td>
			<td>CD510B-1</td>
			<td>used to package the lentivirus expressing EF1a-copGFP</td>
		</tr>
		<tr>
			<td>Dimethylpolysiloxane</td>
			<td>Sigma</td>
			<td>DMPS5X</td>
			<td>culturing embryos</td>
		</tr>
		<tr>
			<td>hyaluronidase</td>
			<td>Sigma</td>
			<td>H3506</td>
			<td>used to remove cumulus cells</td>
		</tr>
		<tr>
			<td>XYClone Laser</td>
			<td>Hamilton Thorne Biosciences</td>
			<td></td>
			<td>perforating mouse fertilized eggs</td>
		</tr>
		<tr>
			<td>Non-Surgical Embryo Transfer (NSET) Device</td>
			<td>ParaTechs</td>
			<td>60010</td>
			<td>NSET of embryos</td>
		</tr>
		<tr>
			<td>KSOM medium</td>
			<td>Millipore</td>
			<td>MR-020P-5F</td>
			<td>culturing embryos</td>
		</tr>
		<tr>
			<td>Composition of KSOM:</td>
			<td></td>
			<td></td>
			<td>mg/100mL</td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td></td>
			<td></td>
			<td>555</td>
		</tr>
		<tr>
			<td>KCl</td>
			<td></td>
			<td></td>
			<td>18.5</td>
		</tr>
		<tr>
			<td>KH2PO4</td>
			<td></td>
			<td></td>
			<td>4.75</td>
		</tr>
		<tr>
			<td>MgSO4 7H2O</td>
			<td></td>
			<td></td>
			<td>4.95</td>
		</tr>
		<tr>
			<td>CaCl2 2H2O</td>
			<td></td>
			<td></td>
			<td>25</td>
		</tr>
		<tr>
			<td>NaHCO3</td>
			<td></td>
			<td></td>
			<td>210</td>
		</tr>
		<tr>
			<td>Glucose</td>
			<td></td>
			<td></td>
			<td>3.6</td>
		</tr>
		<tr>
			<td>Na-Pyruvate</td>
			<td></td>
			<td></td>
			<td>2.2</td>
		</tr>
		<tr>
			<td>DL-Lactic Acid, sodium salt</td>
			<td></td>
			<td></td>
			<td>0.174mL</td>
		</tr>
		<tr>
			<td>10mM EDTA</td>
			<td></td>
			<td></td>
			<td>100&#181;L</td>
		</tr>
		<tr>
			<td>Streptomycin</td>
			<td></td>
			<td></td>
			<td>5</td>
		</tr>
		<tr>
			<td>Penicillin</td>
			<td></td>
			<td></td>
			<td>6.3</td>
		</tr>
		<tr>
			<td>0.5% phenol red</td>
			<td></td>
			<td></td>
			<td>0.1mL</td>
		</tr>
		<tr>
			<td>L-Glutamine</td>
			<td></td>
			<td></td>
			<td>14.6</td>
		</tr>
		<tr>
			<td>MEM Essential Amino Acids</td>
			<td></td>
			<td></td>
			<td>1mL</td>
		</tr>
		<tr>
			<td>MEM Non-essential AA</td>
			<td></td>
			<td></td>
			<td>0.5mL</td>
		</tr>
		<tr>
			<td>BSA</td>
			<td></td>
			<td></td>
			<td>100</td>
		</tr>
		<tr>
			<td>M2 medium</td>
			<td>Millipore</td>
			<td>MR-015-D</td>
			<td>culturing embryos</td>
		</tr>
		<tr>
			<td>Composition of M2:</td>
			<td></td>
			<td></td>
			<td>mg/100mL</td>
		</tr>
		<tr>
			<td>Calcium Chloride</td>
			<td></td>
			<td></td>
			<td>25.1</td>
		</tr>
		<tr>
			<td>Magnesium Sulfate (anhydrous)</td>
			<td></td>
			<td></td>
			<td>16.5</td>
		</tr>
		<tr>
			<td>Potassium Chloride</td>
			<td></td>
			<td></td>
			<td>35.6</td>
		</tr>
		<tr>
			<td>Potassium Phosphate, Monobasic</td>
			<td></td>
			<td></td>
			<td>16.2</td>
		</tr>
		<tr>
			<td>Sodium Bicarbonate</td>
			<td></td>
			<td></td>
			<td>35</td>
		</tr>
		<tr>
			<td>Sodium Chloride</td>
			<td></td>
			<td></td>
			<td>553.2</td>
		</tr>
		<tr>
			<td>Albumin, Bovine Fraction</td>
			<td></td>
			<td></td>
			<td>400</td>
		</tr>
		<tr>
			<td>D-Glucose</td>
			<td></td>
			<td></td>
			<td>100</td>
		</tr>
		<tr>
			<td>Na-HEPES</td>
			<td></td>
			<td></td>
			<td>54.3</td>
		</tr>
		<tr>
			<td>Phenol Red</td>
			<td></td>
			<td></td>
			<td>1.1</td>
		</tr>
		<tr>
			<td>Pyruvic Acid</td>
			<td></td>
			<td></td>
			<td>3.6</td>
		</tr>
		<tr>
			<td>DL-Lactic Acid</td>
			<td></td>
			<td></td>
			<td>295</td>
		</tr>
	</tbody>
</table>

laser-assisted lentiviral gene delivery to mouse fertilized eggs

Lentiviruses are efficient vectors for gene delivery to mammalian cells. Following transduction, the lentiviral genome is stably incorporated into the host chromosome and is passed on to progeny. Thus, they are ideal vectors for creation of stable cell lines, in vivo delivery of indicators, and transduction of single cell fertilized eggs to create transgenic animals. However, mouse fertilized eggs and early stage embryos are protected by the zona pellucida, a glycoprotein matrix that forms a barrier against lentiviral gene delivery. Lentiviruses are too large to penetrate the zona and are typically delivered by microinjection of viral particles into the perivitelline cavity, the space between the zona and the embryonic cells. The requirement for highly skilled technologists and specialized equipment has minimized the use of lentiviruses for gene delivery to mouse embryos. This article describes a protocol for permeabilizing the mouse fertilized eggs by perforating the zona with a laser. Laser-perforation does not result in any damage to embryos and allows lentiviruses to gain access to embryonic cells for gene delivery. Transduced embryos can develop into blastocyst in vitro, and if implanted in pseudopregnant mice, develop into transgenic pups. The laser used in this protocol is effective and easy to use. Genes delivered by lentiviruses stably incorporate into mouse embryonic cells and are germline transmittable. This is an alternative method for creation of transgenic mice that requires no micromanipulation and microinjection of fertilized eggs.

Development of isolated/transduced mouse fertilized eggs can be checked under the microscope daily (Figure 1). Healthy embryos develop into blastocyst within 3&#8211;4 days. In this protocol, 60&#8211;70% of untreated embryos develop into blastocyst23. Out of 114 laser-perforated transduced embryos, 54 developed into blastocyst (rate of 47%) and 46 blastocysts expressed GFP (46/54=85%)23.
The mouse embryos were laser-perforated on the day of harvest. The optimal setting for the laser treatment was 3 holes per fertilized egg and 250 ms. The laser should be aimed to thin the zona instead of creating a hole (Figure 2). This allows the developing embryos to benefit from an intact encapsulating zona pellucida while becoming permissive to lentiviral transduction. In these experiments, mouse embryos were transduced with a recombinant lentivirus that expressed copepod GFP (abbreviated GFP) from an elongation factor 1a promoter. For transduction, 2 uL of lentivirus was introduced into the culture media. Increasing the amount of virus, directly affected the number of transduced embryos that expressed GFP while adversely affecting embryo development into blastocyst23. Viral volumes larger than 10% of KSOM drop volume would also adversely affect blastocyst formation (e.g. greater than 5 &#956;L of virus in a 50 &#956;L KSOM drop).
To validate the viability, transduced mouse embryos were non-surgically transferred to pseudopregnant mice. Six separate NSET events, transferring a total of 58 blastocyst, resulted in 9 GFP transgenic pups out of total of 12, yielding 75% rate of transgenesis 23. The NSET protocol is reported to yield 30-35% live births28 compared to 21% yield that were observed in our experiments (12/58). The lentiviral treatment may have played a role in embryo development and contributed to the low embryo transfer rate. Pups with multiple lentiviral integrations and high expression of GFP were visually green under a blue LED lamp (465-470 nm) (Figure 3). The number of incorporated GFP copies ranged from 0-6 copies and was determined by performing qualitative PCR on isolated chromosomal DNA from pup tissue23.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/58327/58327fig1.jpg" /> 
Figure 1: Development of Transduced Mouse Fertilized Eggs in Culture. The C57BL/6J mouse fertilized eggs were monitored on Day 0 (harvested fertilized egg), Day 1 (two-cell), Day 2 (8-16 cells), Day 3 (morula), and Day 4 (blastocyst). Embryos were transduced with a lentivirus carrying a GFP gene. Presence of Fluorescence in transduced embryos became evident by Day 2-3. <a href="https://www.jove.com/files/ftp_upload/58327/58327fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/58327/58327fig2.jpg" /> 
Figure 2: Laser-Treatment of Mouse Fertilized Eggs. Examples of perforating the zona to produce a hole vs thinning of the zona.
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/58327/58327fig3.jpg" /> 
Figure 3: Transgenic Mice Expressing GFP. Dark Reader (DR Spot Lamp, DRSL-9S) was used to visualize GFP positive pups in a dark environment. Non-transgenic control pups were added to the group for contrast. Resulting pups (red arrows) were genotyped and contained from 0-6 copies of the lentiviral gene/GFP.

Watch this Scientific Journal Video about Laser-assisted Lentiviral Gene Delivery to Mouse Fertilized Eggs at JoVE.com

Laser-assisted Lentiviral Gene Delivery to Mouse Fertilized Eggs | Biology | Video

Laser-assisted Lentiviral Gene Delivery to Mouse Fertilized Eggs

Mouse fertilized eggs and early stage embryos are protected by the zona pellucida, a glycoprotein matrix that forms a barrier against gene delivery. This article describes a protocol for perforating the zona with a laser to transduce embryonic cells with lentiviral vectors and to create transgenic mice.

Lentiviruses are efficient vectors for gene delivery to mammalian cells. Following transduction, the lentiviral genome is stably incorporated into the ...

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7.5K Views.  National Institute of Environmental Health Sciences. Mouse fertilized eggs and early stage embryos are protected by the zona pellucida, a glycoprotein matrix that forms a barrier against gene delivery. This article describes a protocol for perforating the zona with a laser to transduce embryonic cells with lentiviral vectors and to create transgenic mice.

Video: Laser-assisted Lentiviral Gene Delivery to Mouse Fertilized Eggs

Windowing Chicken Eggs for Developmental Studies

The study of development has been greatly aided by the use of the chick embryo as an experimental model.  The ease of accessibility of the embryo has allowed for experiments to map cell fates using several approaches, including chick quail chimeras and focal dye labeling.  In addition, it allows for molecular perturbations of several types, including placement of protein-coated beads and introduction of plasmid DNA using in ovo electroporation.  These experiments have yielded important data on the development of the central and peripheral nervous systems.  For many of these studies, it is necessary to open the eggshell and reclose it without perturbing the embryo's growth.  The embryo can be examined at successive developmental stages by re-opening the eggshell.  While there are several excellent methods for opening chicken eggs, in this article we demonstrate one method that has been optimized for long survival times.  In this method, the egg rests on its side and a small window is cut in the shell.  After the experimental procedure, the shell is used to cover the egg for the duration of its development.  Clear plastic tape overlying the eggshell protects the embryo and helps retain hydration during the remainder of the incubation period.  This method has been used beginning at two days of incubation and has allowed survival through mature embryonic ages.

The ease of accessibility of the embryo has allowed for experiments to map cell fates using several approaches, including chick quail chimeras and focal dye labeling. In this article we demonstrate one egg preparation method that has been optimized for long survival times.

The study of development has been greatly aided by the use of the chick embryo as an experimental model.  The ease of accessibility of the embryo has ...

Obtaining Eggs from Xenopus laevis Females

The eggs of Xenopus laevis intact, lysed, and/or fractionated are useful for a wide variety of experiments. This protocol shows how to induce egg laying, collect and dejelly the eggs, and sort the eggs to remove any damaged eggs.

The eggs of Xenopus laevis intact, lysed, and/or fractionated are useful for a wide variety of experiments. This protocol shows how to induce egg laying, collect and dejelly the eggs, and sort the eggs to remove any damaged eggs.

The eggs of Xenopus laevis intact, lysed, and/or fractionated are useful for a wide variety of experiments. This protocol shows how to induce egg laying, ...

Using the Gene Pulser MXcell Electroporation System to Transfect Primary Cells with High Efficiency

It is becoming increasingly apparent that electroporation is the most effective way to introduce plasmid DNA or siRNA into primary cells. The Gene Pulser MXcell electroporation system and Gene Pulser electroporation buffer (Bio-Rad) were specifically developed to easily transfect nucleic acids into mammalian cells and difficult-to-transfect cells, such as primary and stem cells. We will demonstrate how to perform a simple experiment to quickly identify the best electroporation conditions. We will demonstrate how to run several samples through a range of electroporation conditions so that an experiment can be conducted at the same time as optimization is performed. We will also show how optimal conditions identified using 96-well electroporation plates can be used with standard electroporation cuvettes, facilitating the switch from electroporation plates to electroporation cuvettes while maintaining the same electroporation efficiency. In the video, we will also discuss some of the key factors that can lead to the success or failure of electroporation experiments.

This procedure shows how to use the Gene Pulser MXcell electroporation system to rapidly and easily identify the best electroporation conditions for mouse embryonic fibroblasts (MEFs) or other primary cells. Considerations for troubleshooting are also discussed in the associated video.

It is becoming increasingly apparent that electroporation is the most effective way to introduce plasmid DNA or siRNA into primary cells. The Gene Pulser ...

Using an Automated Cell Counter to Simplify Gene Expression Studies: siRNA Knockdown of IL-4 Dependent Gene Expression in Namalwa Cells

The use of siRNA mediated gene knockdown is continuing to be an important tool in studies of gene expression.  siRNA studies are being conducted not only to study the effects of downregulating single genes, but also to interrogate signaling pathways and other complex interaction networks.  These pathway analyses require both the use of relevant cellular models and methods that cause less perturbation to the cellular physiology.  Electroporation is increasingly being used as an effective way to introduce siRNA and other nucleic acids into difficult to transfect cell lines and primary cells without altering the signaling pathway under investigation. There are multiple critical steps to a successful siRNA experiment, and there are ways to simplify the work while improving the data quality at several experimental stages.  To help you get started with your siRNA mediated gene knockdown project, we will demonstrate how to perform a pathway study complete from collecting and counting the cells prior to electroporation through post transfection real-time PCR gene expression analysis.  The following study investigates the role of the transcriptional activator STAT6 in IL-4 dependent gene expression of CCL17 in a Burkitt lymphoma cell line (Namalwa).  The techniques demonstrated are useful for a wide range of siRNA-based experiments on both adherent and suspension cells.  We will also show how to streamline cell counting with the TC10 automated cell counter, how to electroporate multiple samples simultaneously using the MXcell electroporation system, and how to simultaneously assess RNA quality and quantity with the Experion automated electrophoresis system.

This procedure describes a quick and easy workflow to introduce siRNA into difficult to transfect cell lines and follow gene expression by real-time PCR. Use of an automated cell counter, multi-well electroporation plate, and automated electrophoresis station provide quick and reliable results without the need for expensive robotic handling.

The use of siRNA mediated gene knockdown is continuing to be an important tool in studies of gene expression.  siRNA studies are being conducted not only ...

In vivo Imaging and Therapeutic Treatments in an Orthotopic Mouse Model of Ovarian Cancer

Human cancer and response to therapy is better represented in orthotopic animal models. This paper describes the development of an orthotopic mouse model of ovarian cancer, treatment of cancer via oral delivery of drugs, and monitoring of tumor cell behavior in response to drug treatment in real time using in vivo imaging system. In this orthotopic model, ovarian tumor cells expressing luciferase are applied topically by injecting them directly into the mouse bursa where each ovary is enclosed. Upon injection of D-luciferin, a substrate of firefly luciferase, luciferase-expressing cells generate bioluminescence signals. This signal is detected by the in vivo imaging system and allows for a non-invasive means of monitoring tumor growth, distribution, and regression in individual animals. Drug administration via oral gavage allows for a maximum dosing volume of 10 mL/kg body weight to be delivered directly to the stomach and closely resembles delivery of drugs in clinical treatments. Therefore, techniques described here, development of an orthotopic mouse model of ovarian cancer, oral delivery of drugs, and in vivo imaging, are useful for better understanding of human ovarian cancer and treatment and will improve targeting this disease.

In vivo Imaging and Therapeutic Treatments in an Orthotopic Mouse Model of Ovarian Cancer

Orthotopic animal models of ovarian cancer replicate better human disease and therefore enhance our understanding of cancer progression and tumor response to therapy. A mouse model receives an intrabursal injection of luciferase-expressing ovarian tumor cells. Treatment is administered via oral gavage. Tumor growth is monitored by in vivo imaging system.

Human cancer and response to therapy is better represented in orthotopic animal models.  This paper describes the development of an orthotopic mouse model ...

Isolation and Culture of Cells from the Nephrogenic Zone of the Embryonic Mouse Kidney

Embryonic development of the kidney has been extensively studied both as a model for epithelial-mesenchymal interaction in organogenesis and to gain understanding of the origins of congenital kidney disease. More recently, the possibility of steering na&iuml;ve embryonic stem cells toward nephrogenic fates has been explored in the emerging field of regenerative medicine. Genetic studies in the mouse have identified several pathways required for kidney development, and a global catalog of gene transcription in the organ has recently been generated <a href="http://www.gudmap.org/">http://www.gudmap.org/</a>, providing numerous candidate regulators of essential developmental functions. Organogenesis of the rodent kidney can be studied in organ culture, and many reports have used this approach to analyze outcomes of either applying candidate proteins or knocking down the expression of candidate genes using siRNA or morpholinos. However, the applicability of organ culture to the study of signaling that regulates stem/progenitor cell differentiation versus renewal in the developing kidney is limited as cultured organs contain a compact extracellular matrix limiting diffusion of macromolecules and virus particles. To study the cell signaling events that influence the stem/progenitor cell niche in the kidney we have developed a primary cell system that establishes the nephrogenic zone or progenitor cell niche of the developing kidney ex vivo in isolation from the epithelial inducer of differentiation. Using limited enzymatic digestion, nephrogenic zone cells can be selectively liberated from developing kidneys at E17.5. Following filtration, these cells can be cultured as an irregular monolayer using optimized conditions. Marker gene analysis demonstrates that these cultures contain a distribution of cell types characteristic of the nephrogenic zone in vivo, and that they maintain appropriate marker gene expression during the culture period. These cells are highly accessible to small molecule and recombinant protein treatment, and importantly also to viral transduction, which greatly facilitates the study of candidate stem/progenitor cell regulator effects. Basic cell biological parameters such as proliferation and cell death as well as changes in expression of molecular markers characteristic of nephron stem/progenitor cells in vivo can be successfully used as experimental outcomes. Ongoing work in our laboratory using this novel primary cell technique aims to uncover basic mechanisms governing the regulation of self-renewal versus differentiation in nephron stem/progenitor cells.

In this report we describe a method for the isolation and culture of the progenitor cell niche from the embryonic mouse kidney that can be used to study signaling pathways regulating stem/progenitor cells of the developing kidney. These cultured cells are highly accessible to small molecule and recombinant protein treatment, and importantly also to viral transduction, which allows efficient manipulation of candidate pathways.

Embryonic development of the kidney has been extensively studied both as a model for epithelial-mesenchymal interaction in organogenesis and  to gain ...

Using SecM Arrest Sequence as a Tool to Isolate Ribosome Bound Polypeptides

Extensive research has provided ample evidences suggesting that protein folding in the cell is a co-translational process1-5. However, the exact pathway that polypeptide chain follows during co-translational folding to achieve its functional form is still an enigma. In order to understand this process and to determine the exact conformation of the co-translational folding intermediates, it is essential to develop techniques that allow the isolation of RNCs carrying nascent chains of predetermined sizes to allow their further structural analysis.
SecM (secretion monitor) is a 170 amino acid E. coli protein that regulates expression of the downstream SecA (secretion driving) ATPase in the secM-secA operon6. Nakatogawa and Ito originally found that a 17 amino acid long sequence (150-FSTPVWISQAQGIRAGP-166) in the C-terminal region of the SecM protein is sufficient and necessary to cause stalling of SecM elongation at Gly165, thereby producing peptidyl-glycyl-tRNA stably bound to the ribosomal P-site7-9. More importantly, it was found that this 17 amino acid long sequence can be fused to the C-terminus of virtually any full-length and/or truncated protein thus allowing the production of RNCs carrying nascent chains of predetermined sizes7. Thus, when fused or inserted into the target protein, SecM stalling sequence produces arrest of the polypeptide chain elongation and generates stable RNCs both in vivo in E. coli cells and in vitro in a cell-free system. Sucrose gradient centrifugation is further utilized to isolate RNCs.
The isolated RNCs can be used to analyze structural and functional features of the co-translational folding intermediates. Recently, this technique has been successfully used to gain insights into the structure of several ribosome bound nascent chains10,11. Here we describe the isolation of bovine Gamma-B Crystallin RNCs fused to SecM and generated in an in vitro translation system.

We describe here a technique that is now routinely used to isolate stably bound ribosome nascent chain complexes (RNCs). This technique takes advantage of the discovery that a 17 amino acid long SecM "arrest sequence" can halt translation elongation in a prokaryotic (E. coli) system, when inserted into (or fused to the C-terminus) of virtually any protein.

Extensive research has provided ample evidences suggesting that protein folding in the cell is a co-translational process1-5. However, the exact pathway ...

Intraductal Injection for Localized Drug Delivery to the Mouse Mammary Gland

Herein we describe a protocol to deliver various reagents to the mouse mammary gland via intraductal injections. Localized drug delivery and knock-down of genes within the mammary epithelium has been difficult to achieve due to the lack of appropriate targeting molecules that are independent of developmental stages such as pregnancy and lactation. Herein, we describe a technique for localized delivery of reagents to the mammary gland at any stage in adulthood via intraductal injection into the nipples of mice. The injections can be performed on live mice, under anesthesia, and allow for a non-invasive and localized drug delivery to the mammary gland. Furthermore, the injections can be repeated over several months without damaging the nipple. Vital dyes such as Evans Blue are very helpful to learn the technique. Upon intraductal injection of the blue dye, the entire ductal tree becomes visible to the eye. Furthermore, fluorescently labeled reagents also allow for visualization and distribution within the mammary gland. This technique is adaptable for a variety of compounds including siRNA, chemotherapeutic agents, and small molecules.

A protocol for the non-invasive intraductal delivery of aqueous reagents to the mouse mammary gland is described. The method takes advantage of localized injection into the nipples of mammary glands targeting mammary ducts specifically. This technique is adaptable for a variety of compounds including siRNA, chemotherapeutic agents and small molecules.

Herein we describe a protocol to deliver various reagents to the mouse mammary gland via intraductal injections. Localized drug delivery and knock-down of ...

Transient Expression of Proteins by Hydrodynamic Gene Delivery in Mice

Efficient expression of transgenes in vivo is of critical importance in studying gene function and developing treatments for diseases. Over the past years, hydrodynamic gene delivery (HGD) has emerged as a simple, fast, safe and effective method for delivering transgenes into rodents. This technique relies on the force generated by the rapid injection of a large volume of physiological solution to increase the permeability of cell membranes of perfused organs and thus deliver DNA into cells. One of the main advantages of HGD is the ability to introduce transgenes into mammalian cells using naked plasmid DNA (pDNA). Introducing an exogenous gene using a plasmid is minimally laborious, highly efficient and, contrary to viral carriers, remarkably safe. HGD was initially used to deliver genes into mice, it is now used to deliver a wide range of substances, including oligonucleotides, artificial chromosomes, RNA, proteins and small molecules into mice, rats and, to a limited degree, other animals. This protocol describes HGD in mice and focuses on three key aspects of the method that are critical to performing the procedure successfully: correct insertion of the needle into the vein, the volume of injection and the speed of delivery. Examples are given to show the application of this method to the transient expression of two genes that encode secreted, primate-specific proteins, apolipoprotein L-I (APOL-I) and haptoglobin-related protein (HPR).

In vivo transfection of naked DNA by hydrodynamic gene delivery introduces genes into the tissue of an animal with minimal inflammatory response. Sufficient amounts of gene product are generated such that gene function and regulation as well as protein structure and function can be analyzed.

Efficient expression of transgenes in vivo is of critical importance in studying gene function and developing treatments for diseases. Over the past ...

Phage-mediated Delivery of Targeted sRNA Constructs to Knock Down Gene Expression in E. coli

RNA-mediated knockdowns are widely used to control gene expression. This versatile family of techniques makes use of short RNA (sRNA) that can be synthesized with any sequence and designed to complement any gene targeted for silencing. Because sRNA constructs can be introduced to many cell types directly or using a variety of vectors, gene expression can be repressed in living cells without laborious genetic modification. The most common RNA knockdown technology, RNA interference (RNAi), makes use of the endogenous RNA-induced silencing complex (RISC) to mediate sequence recognition and cleavage of the target mRNA. Applications of this technique are therefore limited to RISC-expressing organisms, primarily eukaryotes. Recently, a new generation of RNA biotechnologists have developed alternative mechanisms for controlling gene expression through RNA, and so made possible RNA-mediated gene knockdowns in bacteria. Here we describe a method for silencing gene expression in E. coli that functionally resembles RNAi. In this system a synthetic phagemid is designed to express sRNA, which may designed to target any sequence. The expression construct is delivered to a population of E. coli cells with non-lytic M13 phage, after which it is able to stably replicate as a plasmid. Antisense recognition and silencing of the target mRNA is mediated by the Hfq protein, endogenous to E. coli. This protocol includes methods for designing the antisense sRNA, constructing the phagemid vector, packaging the phagemid into M13 bacteriophage, preparing a live cell population for infection, and performing the infection itself. The fluorescent protein mKate2 and the antibiotic resistance gene chloramphenicol acetyltransferase (CAT) are targeted to generate representative data and to quantify knockdown effectiveness.

Phage-mediated Delivery of Targeted sRNA Constructs to Knock Down Gene Expression in E. coli

We describe a method to knock down gene expression in a growing population of E. coli cells using sequence-targeted sRNA expression cassettes delivered by an M13 phagemid vector.