This method can help answer key questions in the ovary research field about follicle development, follicle atresia and operation. The main advantage of this technique is that we can reproduce the ovarian phenomena under controlled culture conditions for the observation in real time. To prepare the ovaries from a four week old Institute of Cancer Research mouse for culture:Use scissors and tweezers to trim the surrounding tissue from the ovaries under a stereo microscope, and place the cleaned ovaries into a dish of fresh culture medium.
When all of the ovaries have been trimmed, transfer the individual ovaries onto a piece of filter paper moistened with 37 degrees Celsius PBS, and use a microtome blade to slice each ovary into four pieces. Transfer the slices into a 3.5 centimeter dish of 37 degrees Celsius culture medium, and use a micropipette to add an about 0.5 micrometer droplet of culture medium onto one cell culture insert per ovarian tissue section. In a second 3.5 centimeter glass bottom cell culture dish containing one millimeter of medium:Using tweezers, transfer one tissue specimen into each droplet and place the plate in a cell culture incubator.
Replace the supernatant in the dish with fresh 37 degrees Celsius culture medium every two days and treat the ovaries with 100 milliunits per milliliter of FSH and LH for 12 hours every fourth day. Begin imaging the cultured ovaries every 24 hours after one day of culture to allow sufficient follicle growth between imaging sessions;capturing images at 30 minute intervals using a time-lapse imaging system under the appropriate experimental conditions. To analyze ovarian follicle development:Open the images in ImageJ and open the analyze menu to select set scale.
Enter the side lengths of the captured images and the corresponding numbers of pixels in the known distance and distance in pixels fields, respectively. Then, use the free-hand tool to outline the follicles and click measure. During a three week ovarian tissue slice culture period, most antral and secondary follicles are degenerated by follicle atresia, and some are ovulated.
Some follicles develop in groups during each LH surge cycle. While the timing of ovulation and the number of ovulated oocytes differs between mouse ovaries, ovulation from cultured ovaries predominantly occurs within 48 hours of each LH surge. Note that not all ovulated oocytes release first polar bodies after ovulation.
Primordial and primary follicles are present simultaneously in postnatal day four mouse ovaries. Whereas, only primordial follicles are present in postnatal day zero ovaries. However, primary follicles become detectable in cultured postnatal day zero ovaries after 30 to 40 hours of culture as demonstrated.
Primordial and primary follicles can also be distinguished in the cultured ovaries isolated from mCherry transgenic animals by the mCherry positive nuclei of granulosa cells;allowing the tracking of the follicle stages in the ovary slice cultures. I hope that this technique paves the way for researchers in the field of reproductive technology to explore new techniques for fertility treatment.
