Fertility declines with age in most female mammals, but naked mole rats can develop new eggs as adults, enabling them to remain fertile throughout their lives
Unlike most mammals, female naked mole rats develop new eggs throughout their entire lives – a finding that could lead to improvements in human infertility research.
“This animal is the opportunity to think about and develop new techniques or potential targets for making new drugs, because their [reproductive] cells have the same program that we have in mice and humans, but they’re behaving differently,” says Miguel Angel Brieño-Enríquez at the University of Pittsburgh in Pennsylvania.
Native to East Africa, naked mole rats (Heterocephalus glaber) live for up to 37 years and form underground colonies with social structures similar to those of bees, including a single queen that produces offspring for her entire life. By contrast, mice only live for about four years and their fertility starts dropping when they are only 9 months old.
Curious about these differences in reproductive lifespans, Brieño-Enríquez and his colleagues looked at the ovaries of naked mole rats under a microscope when the animals were 1, 5, 8, 15, 28 and 90 days old. They used advanced staining and testing techniques to identify the different kinds of cells they saw. In particular, they were looking for germ cells that can divide and mature into oocytes – or eggs – through a process known as oogenesis.
In humans, mice and other mammals, oogenesis only occurs before birth and, in some species, shortly afterwards, leaving newborn females with a limited lifetime supply of eggs. Those eggs gradually die over time, leading to reduced fertility with age.
In the naked mole rats, though, Brieño-Enríquez and his colleagues found large numbers of germ cells at every stage of life they tested, with numbers steadily increasing throughout the first week of life. At 8 days old, the naked mole rats had an average of 1.5 million egg cells – 95 times more than 8-day-old mice, says Brieño-Enríquez.
The researchers then grew ovary sections of young animals in their laboratories and observed ongoing oogenesis. Combined with the team’s previous discovery of germ cells even in 10-year-old mole rats, the observations suggest that naked mole rats can continually replenish their egg supply.
Because any young female mole rat can become the colony’s next queen, the researchers then tested the worker females’ potential fertility by removing 3-year-old females from their colonies and placing them in individual cages with a male for four weeks. The animals became fertile like queens, says Brieño-Enríquez. Investigations under the microscope showed that worker females have germ cells in their ovaries, but oogenesis only begins when the worker transitions to a queen.
The study provides “very useful insight”, which will certainly be “a substantial contribution to the field”, says Scott Sills at the Center for Advanced Genetics in California. “If this could be transformed into a clinical application [for humans], then not only would it have a very meaningful role in infertility practice, but it would basically reset the whole paradigm for how we treat menopause,” he says. “Symptomatic menopause would no longer be hostage to [hormone] replacement therapy.”
But how exactly that information can translate into contributions to human medicine remains to be seen, says Aspasia Destouni at Aristotle University of Thessaloniki in Greece. “I see this as an exciting opportunity to manipulate a new model organism that has more accessible samples [for human reproduction research],” she says. “But we have to be cautious about the excitement level, because people might think that this is an answer to menopause… but clearly, they’re not there yet.”
Sign up to Wild Wild Life, a free monthly newsletter celebrating the diversity and science of animals, plants and Earth’s other weird and wonderful inhabitants
More on these topics: