A little-known structure in the female reproductive system, long dismissed as useless, may actually play a critical role in ovarian development and fertility, according to a new study in mice.
The structure, known as the rete ovarii (RO), was first discovered in humans over a century ago. It was thought to be a vestigial organ—an evolutionary leftover with no real function in modern anatomy. However, new research published on March 19 in the journal eLife challenges that assumption.
Using advanced imaging and molecular techniques, researchers revealed that the rete ovarii is far from redundant. In fact, it may be a vital player in ovarian function, and by extension, female fertility.
“The female reproductive tract is often thought to consist of the vulva, vagina, cervix, uterus, oviduct, and ovaries,” the authors wrote. “We suggest that the RO be added to this list and investigated as an additional component of female reproductive function.”
What Is the Rete Ovarii?
The RO is a horseshoe-shaped network of microscopic tubes located beneath the ovary, near the area where blood vessels and nerves enter. Despite its presence in many mammals—including cows, cats, pigs, and monkeys—it was historically overlooked due to the limits of 19th-century science.
“When this structure was first discovered in the late 1800s, it was assumed to have no purpose because its function wasn’t obvious,” explained Adam Taylor, a professor of anatomy at Lancaster University, who was not involved in the study.
Now, using modern tools such as microscopy, imaging, and molecular analysis, researchers have uncovered its complex structure and function.
Key Findings from the Study
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The RO is composed of three distinct regions:
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Intraovarian rete (IOR): Located within the ovary.
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Extraovarian rete (EOR): A network of convoluted tubes ending in a bulb-like structure.
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Connecting rete (CR): A transitional area between the IOR and EOR.
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These regions develop during fetal life and persist into adulthood.
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Using mass spectrometry, researchers found the EOR produces thousands of proteins. One key protein, IGFBP2 (insulin-like growth factor-binding protein 2), may help regulate insulin-like growth factors involved in follicle development—crucial for egg maturation and hormone production.
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In another test, fluorescent dye was tracked moving through the EOR, suggesting that fluid is actively transported toward the ovary, possibly helping regulate its environment.
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The cells in the RO also express hormone receptors for estrogen and progesterone—two major reproductive hormones that regulate the menstrual cycle and support fertility.
Implications for Human Reproductive Health
Although the study was conducted in mice, the scientists believe the findings could be relevant to humans. Humans and mice share similar sex-organ development pathways, and the RO exists across many mammalian species.
This discovery could reshape how scientists view the female reproductive system—and potentially open up new avenues for understanding infertility and ovarian disorders.
Source: Science Daily
