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Innovative images capture ovulation in action. Here’s why it matters

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Innovative images capture ovulation in action. Here’s why it matters

The advancement of science is a funny thing. We may know a lot about alpaca sex, but when it comes to how human babies are made, there are still gaps in our knowledge. Now, biologists at the Max Planck Institute for Multidisciplinary Studies have filled in a big blank about one of the earliest phases of the reproductive cycle.

Most of the playback process is pretty straightforward, and if you don’t know the basics, you might be in for a very awkward conversation with your parents. But what happens before the eggs begin their journey down the fallopian tubes has been a mystery, even to biologists. The eggs are small, only 0.12 millimeters (0.005 in) in diameter, making them difficult to see inside the body. Because they are released quickly from one of the two ovaries (with no way to predict which), there has never been a clear view of the release of an egg. Max Planck scientists devised a method to witness this stage, a breakthrough that could one day lead to new fertility treatments.

In all mammals, including humans, each egg is housed in a small fluid-filled sac inside the ovaries called an ovarian follicle. During a fertile cycle, more than 30 eggs mature, but only the most developed follicles rupture and release the egg. Biologists noted in the journal Nature Cell Biology that while genetic studies, animal dissections, and cultured samples have provided insight into this process, nothing compares to video imaging for studying biological processes.

To finally see how an egg is released from its follicle, the researchers took ovarian tissue from some mice that had been genetically modified to produce eggs that were easy to see on camera. They placed the tissue samples in dishes with powerful camera lenses and induced ovulation by exposing the ovarian cells to two key hormones involved in reproduction and development.

What they witnessed was a multi-step process involving an interplay of muscle contractions and the release of very specific chemicals, ultimately producing an egg. “We can distinguish three phases,” said Melina Schuh, director of the Max Planck Institute, who worked on the study, in a statement. “The follicle expands, contracts and finally releases the egg.”

During the expansion process, cells inside the follicle, called cumulus cells, produced a chemical called hyaluronic acid that flowed into the follicles. When the biologists altered the tissue to prevent hyaluronic acid from being produced, follicle growth was stunted and ovulation did not occur.

Once the follicle had grown large enough, the muscle tissue inside it began to contract. Finally, the surface of the follicle was opened, so, in a way, the famous scene alien it’s not that far off as a metaphor for reproduction. In fact, the video of a follicle bursting looks more like another alien-themed movie: Starship Troopersin which gigantic insects launched glowing projectiles from their butts.

“When the follicle ruptures, which happens in the third phase, the egg is released and ovulation is complete,” said Tabea Lilian Marx, a doctoral student at the institute who also work in the studio. “The surface of the follicle bulges outward and eventually ruptures, releasing the follicular fluid, the cumulus cells, and eventually the egg.”

In the study, the team expressed excitement about what their technique for observing ovulation could mean for the study of fertility. Future research could focus on what happens when ovarian follicles are exposed to different chemicals and drugs. Given the precarious state of fertility treatment in the United States, this can only be a good thing.

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