by Amanda Morris, Northwestern University
Male
pheromones just might be the fountain of youth for aging female
animals' eggs, according to a new Northwestern University study.
In the new study, researchers used the tiny transparent roundworm C. elegans, a well-established model organism commonly used in biology research. Exposure of female roundworms to male pheromones slowed down the aging of the females' egg cells, resulting in healthier offspring.
Not
only did the exposure decrease embryonic death by more than twofold, it
also decreased chromosomal abnormalities in surviving offspring by more
than twofold. Under the microscope, egg cells also looked younger and
healthier, rather than tiny and misshapen, which is common with aging.
The
researchers believe this finding potentially could lead to
pharmacological interventions that would combat infertility issues in
humans by improving egg cell quality and delaying the onset of
reproductive aging.
"Reproductive
aging affects everyone," said Northwestern's Ilya Ruvinsky, who led the
study. "One of the first signs of biological aging is the decreased
quality of reproductive cells, which causes reduced fertility, increased
incidence of fetal defects including miscarriages, and eventually loss
of fertility. By all criteria we could think of, male pheromones made
the eggs better."
The paper was published this week (May 16) in the Proceedings of the National Academy of Sciences.
Ruvinsky
is a research associate professor of molecular biosciences at
Northwestern's Weinberg College of Arts and Sciences. Erin Aprison, a
research associate in Ruvinsky's laboratory, is the paper's first
author. Svetlana Dzitoyeva and David Angeles-Albores are paper
co-authors.
Shifting energy to reproduction
To conduct the study, the team aged female roundworms in the presence of a pheromone that
is normally produced by male roundworms. The researchers saw that egg
quality in females exposed to the pheromone was higher than in control
roundworms that did not encounter the pheromone.
Although
continuous exposure to male pheromones worked best, even shorter
exposure improved overall egg quality. Ruvinsky believes this result can
be explained by the animals' "shifting energy budgets."
Acting
outside the body, pheromones are chemicals that animals produce and
release to elicit social responses from other members of their species.
According to Ruvinsky, pheromones also inform animals about how to
budget their finite energy.
When
conditions are not conducive to reproduction, female animals will spend
resources and energy maintaining their overall body health, including
muscles, neurons, intestines and other nonreproductive organs. Sensing
male pheromones triggers downstream signaling from the nervous system to the rest of the body, causing the female animals to shift their energy and resources to increasing reproductive health instead. The result? Better eggs but faster decay of the body.
"The
pheromone tricks the female into sending help to her eggs and
shortchanging the rest of her body," Ruvinsky said. "It's not all or
nothing, but it's shifting the balance."
Salvaging recycled eggs
When
female roundworms spent more energy on reproduction, they produced more
egg cell precursors from stem cells. And, in a seemingly
counterproductive move, most of these cells actually died. But Ruvinsky
says this is not a mistake but a cleverly designed advantage.
"The majority of egg precursors die, and the spare parts are
recycled to build better eggs," he said. "We think that is essentially
what's happening. Production is increased. Most egg precursors die, and
their parts are salvaged and recycled into a few, higher-quality eggs."
Of
course, there are unfortunate trade-offs. When female roundworms
neglected the rest of their body to focus their energy on reproductive
health, they were more likely to experience early death. Ruvinsky said
this information, too, can advise future drug development for humans.
"The
pheromones that roundworms use are not found in humans," he said. "But
the neurons they activate are very similar. We are working to design
pharmacological interventions that manipulate these neurons to improve
fertility while reducing the negative side effects. It remains to be
seen, but it's definitely worth trying."
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