To begin, prepare drops of M2 IBMX Medium in a plastic tissue culture dish, and place the dish on a hot block at 37 degrees Celsius for at least 30 minutes before oocyte isolation. Dissect the ovaries of the euthanized mice and place them in a five milliliter round bottom tube with M2 IBMX. Transfer the ovaries to a plastic lid containing 1.5 milliliters of M2 IBMX.
Remove any peri-ovarian adipose tissue, or fallopian tube segments, and release the cumulus oocyte complexes by mechanical perforation of the ovaries with a 27-gauge needle. Transfer the cumulus oocyte complexes to a culture dish with drops of M2 IBMX. And remove the cumulus cells by repeated pipetting using a narrow bore glass pasture pipette.
Select the surrounded nucleus germinal vesicle or GV stage oocytes, and transfer them in a drop of M2 IBMX medium on hot block at 37 degrees Celsius protected from light. After inducing double strand breaks using etoposide, place the GV stage oocytes in drops of the genotoxic agent for one hour on the hot block in the dark. Add drops of M16 culture medium supplemented with 400 micromolar IBMX to the oocytes to keep them arrested for a prolonged period.
Place the oocytes in an incubator at 37 degrees Celsius and 5%carbon dioxide.
