The rete ovarii has long been overlooked as a leftover from embryonic development. But new research suggests this small structure may be doing more than scientists once thought. In mice, researchers found that it secretes proteins and transports fluid towards the ovary.

These findings, published in eLife in March 2025, offer a new perspective on a structure whose purpose has remained largely unexplored. They also raise questions about whether the rete ovarii plays a role in ovarian health and fertility, although its exact function is still unclear.

What Is the Rete Ovarii?

The rete ovarii is a network of small, tube-like structures connected to the ovary. Despite appearing in early anatomical references, it largely disappeared from modern textbooks as scientists regarded it as a functionless remnant.

Interest in the structure grew after developmental biologist Jennifer McKey noticed it while examining entire mouse ovaries under a microscope in 2022. Subsequent research investigated its anatomy and potential biological functions.

The team identified three regions that persist into adulthood: the intraovarian rete, the extraovarian rete, and the connecting rete. Together, they form a structure that could provide a pathway for communication between the ovary and its surrounding environment.

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How Could It Influence Fertility?

To investigate the structure's function, researchers injected dextran into the dilated tip of the extraovarian rete, the part of the structure outside the ovary. They observed fluid moving towards the ovary, suggesting that the rete ovarii may help transport fluid towards the organ.

The researchers also analysed proteins within the fluid. Their investigation identified thousands of proteins in the collected material, although many could have originated from surrounding cells or damaged tissue. After applying additional screening methods, they identified 15 candidate proteins likely to be secreted by the structure.

Some candidate proteins are involved in protein transport and cellular signalling. These findings suggest that the rete ovarii may participate in communication between the ovary and its surrounding environment, although its precise role remains unclear.

Researchers are particularly interested in whether this activity contributes to follicle development, egg maturation, or the maintenance of ovarian tissue. These processes are important for reproductive health, but further experiments are needed to establish whether the rete ovarii directly influences them.

Could This Explain Unexplained Infertility?

Infertility can result from several factors, including problems with ovulation, reproductive anatomy, hormonal regulation and egg quality. In some cases, investigations do not identify a clear cause.

The rete ovarii offers researchers another structure to investigate when studying ovarian function. If future studies establish how it communicates with ovarian tissue, scientists may gain a better understanding of biological processes involved in reproduction.

However, the findings do not show that dysfunction of the rete ovarii causes unexplained infertility, nor do they provide a new diagnostic test or treatment.

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