Naked mole-rats are an anomaly in more ways than one, and the author of a new study on the creature, which manages to outlive all other rodents, explains why: "They almost never get cancer, they don't feel pain like other mammals, they live in underground colonies, and only the queen can have babies." That baby part is what Miguel Brieño-Enríquez was compelled to investigate: Unlike most other mammals, naked mole-rats "never stop having babies," he explained, but scientists were at a loss as to why—until now. In a study published Tuesday in Nature Communications, Brieño-Enríquez and his team explain that a limitless supply of egg cells is a driver.
As LiveScience explains, "The findings challenge the belief that mammals have a limited reserve of egg cells, established before or shortly after birth, and not replenished thereafter." That limited reserve is the case for humans, mice, and most female mammals. As a press release explains, those egg cells are produced in utero through a process known as oogenesis. That limited supply of egg cells dwindles over time: Some are released during ovulation but the majority simply die. But naked mole-rat females are born with zero.
It turns out they produce a huge amount of them as pups, and continue to. A comparison with mice provides context: The two are about the same size, but mice begin to experience a drop in fertility by nine months; naked mole-rats retain their fertility for lives that can stretch longer than 30 years. At 8 days old, a naked mole-rat female has an average 1.5 million egg cells; that's 95 times what an 8-day-old female mouse has. And there could be potential implications for human health. "Their [reproductive] cells have the same program that we have in ... humans, but they’re behaving differently," Brieño-Enríquez tells New Scientist.
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A female naked mole-rat isn't born a queen, but rises to the position via competition upon a queen's death. To mimic that scenario, the researchers took 3-year-old females from their colony to trigger reproductive activation and found the egg precursor cells in their ovaries only began dividing following a transition to queen. "If we can figure out how they’re able to do this, we might be able to develop new drug targets or techniques to help human health," said Brieño-Enríquez. "Even though humans are living longer, menopause still happens at the same age. We hope to use what we are learning from the naked mole-rat to protect ovary function"—a goal that's about more than fertility, as ovary health "influences cancer risk, heart health, and even lifespan," per the release. (More discoveries stories.)
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