Groundbreaking footage captures ovulation in action. Here’s why it’s important

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

Most of the breeding process is pretty simple, and if you don’t know the basics, you might be late for a very uncomfortable conversation with your parents. But what happens before the eggs begin their journey through the fallopian tubes remains mysterious, even to biologists. The eggs are tiny (only 0.005 inches (0.12 millimeters) in diameter), making them difficult to observe inside the body. Since they are released rapidly from one of two ovaries (with no way to predict which one), there has never been a clear view of an egg being released. Max Planck scientists have devised a method to observe this stage, an advance that could one day lead to new fertility treatments.

Every month one #egg is ovulated from #ovarybeginning the journey of reproduction. But how does ovulation occur?🥚

Our latest work in @NatureCellBio led by @LastChrisThomas And @Tabea_Marxdescribes the control of #ovulation using live imagery.https://t.co/EYjwLfdAdy (1/7) pic.twitter.com/69QcE673UL

– Schuh Lab (@SchuhLab) October 16, 2024

In all mammals, including humans, each egg is housed in a small, fluid-filled sac inside the ovaries called the 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 Natural cellular biology that while genetic studies, animal dissections and cultured samples have provided insight into this process, nothing compares to video footage for studying biological processes.

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

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

During the expansion process, cells inside the follicle, called cumulus cells, produce a chemical called hyaluronic acid that flows into the follicles. When biologists modified the tissues to prevent the production of hyaluronic acid, follicle growth was delayed and ovulation did not occur.

Once the follicle grew large enough, the muscle tissue within it began to contract. Eventually the surface of the follicle opened – thus, in a way, the famous scene of Stranger isn’t that far away as a metaphor for reproduction. In fact, the video of a popping follicle looks more like something from another alien-themed movie: Space Soldiersin which gigantic insects launched luminous projectiles from their butts.

“When the follicle ruptures, which happens during the third phase, the egg is released and ovulation is complete,” said Tabea Lilian Marx, a doctoral student at the institute, who also worked on the study. “The surface of the follicle swells outward and eventually ruptures, releasing follicular fluid, cumulus cells and, finally, the egg.”

In the study, the team expressed excitement about what their ovulation observation technique 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 treatments in the United States, this can only be a good thing.