The overall goal of this procedure is to effectively deliver solutions into the cytoplasm of livestock zygotes using a blunt-end needle with the aid of a laser. This method is used in research and in the animal trans-genesis field, since one is associated with a genome-editing tool, such as a CRISPR Cas9 system, it can create new cows to study gene function and transgenic animals in a very simple and reliable way. The main advantage of this technique is that it can be used to deliver any solution into a cytoplasm of large animal's zygotes.
With a handy person's injection efficiency minimalizes animal liver lomotil rates. First, prepare the injection micropipette by placing a borosilicate glass capillary into a micropipette puller and locking it into place. Use an appropriate program to pull the capillary so it results in a thin tip with a long taper.
Then, carefully remove the pulled pipettes from the device and place them onto a microforge in a horizontal position. Bring the pulled pipette and the microforge heater filament, with it's glass bead, into focus. Use the eyepiece reticle to measure the desired thickness, and move the pipette horizontally until the heater filament reaches the target inner diameter of five micrometers.
Adjust the heat to about 45%and gently bring the pipette down so it touches the filament. Then, briefly activate the heater. This will slightly melt the pipette so it adheres to the filament, and upon cooling, the pipette will break at the contact point, generating a straight cut.
Setting the right temperature is key in this step. Temperatures too high will bend the pipette, while temperatures too low will not be sufficient for cutting the pipette. Next, make an approximate 30 degree angle near the pipette tip by positioning the tip about 10 micrometers away from the heater filament.
Set the temperature to 60%and activate the heater so that the pipette bends over the filament to the desired angle. Using the settings shown here, pull a glass capillary that results in a micro-pipette having a thin tip with a long, even taper and parallel walls. Carefully remove the pulled pipette from the puller device and place it on the microforge holder in a horizontal position.
Use the eyepiece reticle to measure the pipette diameter and move the pipette until its diameter over the filament reaches 180 micrometers. Mark the glass capillary with a diamond-tipped pen and then gently press on the pulled tip to break the glass. This should result in a straight cut.
Next, move the pipette to a vertical position, with its tip close to the filament. Set the temperature of the microforge to 60%and fire-polish the tip of the pipette, using standard techniques until the inner diameter reaches the target size. Measure the inner diameter of the pipette, which should be 40 micrometers.
Using the same procedure as before, bend the tip to a 30 degree angle. Insert the holding pipette into the left micro-manipulator holder and the injection pipette into the right micro-manipulation holder. Then, fill the injection pipette with oil.
Use the micro-manipulator controls to bring the pipettes into the center of the microscope's field of view. Using 4X magnification, check that the micro-pipette tips are at the correct angle so that they are parallel to the bottom of the dish. Place a 50 microliter drop of 37 degree celsius SOF-HEPES solution, that is supplemented with 20%FBS onto the center of the lid of a 100 millimeter petri dish.
Then, place a one to two microliter drop of the solution to be injected close to the injection drop. Next, cover the drops and the injection plate using approximately 10 milliliters of mineral oil. Place the plate on the microscope stage and use a microdispenser to load about 20 to 30 zygotes in the upper side of the injection drop.
Using the 4X objective, load the solution to be injected into the injection pipette by applying negative pressure to the microinjector. Load a sufficient amount of solution to inject two to three zygotes and then move to the injection drop. Within the injection drop, move the holding pipette so the tip gets close to a zygote.
Apply negative pressure with the holding micro-injector so the zygote gets fixed to the holding pipette. Once the zygote is secure, change to a 20X objective. Check that the injection pipette is positioned on the embryo's mid-plane by gently touching the zygote on the site of injection.
If it is not on its mid-plane, the needle will tend to make the embryo rotate, instead of puncture. Next, use software to place the laser vertical in the zona pellucida where the hole will be made. Once correctly positioned, use the laser control window and click on the FIRE button.
Ensure that the size of the hole is large enough to create an opening in the zona pellucida for the needle to pass through without damaging the plasma membrane. Pass the injection needle through the hole in the zona pellucida and make contact with the plasma membrane. Continue pushing the pipette forward until the needle is 3/4 of the way into the embryo.
Observe the position of the meniscus at the solution oil interphase. This will be used to consistently control the injection volume. Apply negative pressure on the injection pipette to aspirate the plasma membrane and cytoplasm into the injection needle.
Continue until the movement of cytoplasm in the needle accelerates or when cytoplasm content, mixing with the injection solution, can be seen. These will indicate breakage of the plasma membrane. Inject back the cytoplasmic content, followed by the solution into the cytoplasm of the zygote, by applying positive pressure until the meniscus at the solution oil interphase has advanced one zygote's diameter equivalent past the starting point.
Then, change to a 4X objective, and move the injected embryo to the lower side of the injection drop. Release the embryo by applying positive pressure on the holding micro-injector. Collect the injected embryos using a micro-dispenser.
Wash the injected embryos by moving them through the three drops of SOF-HEPES and culture them, as described in the accompanying text protocol. Successful delivery of the solution is visible in the fluorescent image, where dexion red is used to track the site of injection and injection efficiency and accuracy. Here, the dye is homogeneously distributed in the cytoplasm, which is typical when using this technique.
This protocol has minimal lysis rates in bovine and ovine zygotes. Few of the injected embryos were lysed in cattle, or sheep as a result of microinjection. Also, there are no statistically significant differences in blastocyst development rates in the control versus injected groups for both bovine and ovine embryos.
Once mastered, this technique can be done at the rate of two embryos per minute. With a handy person injection efficiency, minimalizes animal blastocyst rates. After watching this video, you should understand how to perform laser-assisted intracytoplasmic micro-injection in livestock zygotes.
And also how to use positive and negative suction pressure to assure the rupture of the plasma membrane for an efficient delivery.
