The overall goal of this zygotic FRAP or zFRAP is to examine the association between zygotic chromatin looseness and embryonic development potential to term. This method can help answer key questions in the developmental biology field, such as embryonic development. The main advantage of this technique is that it allows the analyzed zygote to develop to full term without significant damage.
Visual demonstration of this method is critical as the zFRAP analysis steps are difficult to learn because the experimental condition setting and operation for this analysis are very complex. After preparing eGFP-H2B RNA according to the text protocol, use nuclease-free water to dilute it to 250 nanograms per microliter. In a 60-millimeter dish, place two to three drops each of PVP-HTF, five to six drops of Hepes-buffered CZB, and eGFP-H2B mRNA.
Then, use mineral oil to cover the drops. Using a pipette puller, pull borosilicate glass. After breaking the tip, use a microforge to bend the glass pipette to around 30 degrees.
Prior to microinjection, confirm that the plate heater on the stage of the micromanipulator is off to prevent killing the zygotes during mRNA injection. Then, using 10%PVP-HTF, wash and coat the inside of the injection needles. Next from the tips fill the glass capillaries with the diluted eGFP-H2B mRNA.
Collect the fertilized zygotes with a second polar body, and transfer 20 to 25 of them on to the chamber of the microscope stage. Then, with a holding pipette, hold the zygote and break the zona pellucida and the cytosolic membrane with a piezo drive. Inject about 10 picoliters of mRNA into the cytoplasm of each zygote.
Complete the injections within 10 minutes to prevent damage caused by culturing the zygotes outside of the incubator. 10 minutes after microinjection, wash the zygotes in at least three drops of CZB and culture them at 38 degrees Celsius until FRAP analysis. One hour prior to zFRAP analysis, turn on the laser and hot plate attached to the stage of the confocal microscope.
Set the temperature to 38 degrees Celsius. On a 60-millimeter glass-bottomed dish, pipette six to 10 microliters of Hepes-buffered CZB medium and cover it with mineral oil. Then, warm the dish on the heater until zygote collection.
To make it easy to find the zygote with the confocal microscope, it is important to put the drops throughout the center of the dish. Eight to 12 hours after insemination, collect five to 10 eGFP-H2B expressing zygotes and transfer them to a six to 10-microliter drop of pre-warmed Hepes-buffered CZB medium. To perform a precise quantitative analysis it is important to put the zygote toward the center of the Hepes-buffered CZB drops.
Set the bleaching and imaging conditions according to the manufacturer's instructions. For example, under Acquisition Setting, set the scanning speed to four microseconds per pixel and the size to five hundred and twelve. Increase the digital zoom to five, open the DyeList"and choose eGFP"Then, set the observation time to one point six seconds and the number of pictures to 12.
Next, start the Stimulus Setting"panel and on UseScanner"click Main"Set the scanning speed to 10 microseconds per pixel. Click Activation in Series"Set PreActivation"to three frames and activation time to five seconds. Then, click Focus x2"and click Stop"Under the stimulus setting panel click Clip Rect"Set the ROI to 40 by 40 pixels.
Click Time"and XY"Then, use an optical power meter to access the laser power. It is important to have the lights turned off when measuring the laser. After adjusting the laser gage to set the bleaching and imaging laser power, on the toolbar click Live"and then start Live Plot"Place the oil on the objective lens.
Set the chamber on the stage and then find the zygotes in the drops. After finding zygotes, determine the ROI position by clicking Focus x2"And then in the Live Plot"window adjust the HV power gage for the eGFP"channel fluorescence intensity to around 2, 000. To start the zFRAP analysis, click XY"After FRAP analysis, click Series Done"Obtain the FRAP analyzed data, then click on Save As"to save the file 2D View image"as a preferred named file.
Use Copy"ROI and Paste"ROI to prepare a reference region and to background respectively. Next, select ROI, REF, and BG, and then in the 2D View"image window, click Series Analysis"Obtain RoFRAP data and then in the Live Plot"window click the Save"button. Carry out data calculations according to the text protocol.
Eight to 12 hours after insemination, zygotes with two pronucleai showing the expression of eGFP-H2B"were collected and subjected to zFRAP analysis. After bleaching, the intensity of the eGFP-H2B fluorescent signal recovered slightly because of the inflow of eGFP-H2B into the ROI from the unbleached area in the nucleoplasm. Recovery curves reveal that male pronucleai recovered more quickly and with more mobile fractions than female pronucleai.
As demonstrated in these images and graph, after zFRAP analysis, washed and cultured zygotes in CZB medium developed to the blastocyst stage without significant damage. To analyze the full term development, embryos at the two-cell stage were transferred into the ovoducts of pseudo-pregnant mothers. As reported in this table, the birth rate of zFRAP analyzed embryos was slightly, but significantly lower than that of intact embryos but was the same as that of the no zFRAP control.
In addition, the pups derived from zFRAP analyzed zygotes seemed healthy and fully developed. While attempting this procedure, it's important to remember to wait for the other expansion. All budget objectorance to avoid focus drift.
After watching this video, you should have a good understanding on how to analyze chromatin looseness in zygotes.
