The hard-working precursor cells that produce sperm just can’t catch a break. Since men make sperm throughout their lives, these cells have to divide again and again, sending one copy of themselves off to become sperm cells each time. DNA doesn’t always copy itself perfectly, so over the years, genetic errors pile up. And now a new study has quantified just how many mutations sperm will accumulate—and pass on to any offspring—for fathers of various ages. Scientists think that these mutations may be partly to blame for the fact that children with older fathers tend to have higher rates of bipolar disorder, schizophrenia, and autism.
The researchers chose to examine the sperm of crickets, because, as with humans, you can get samples of it without having the male come into contact with a female first.
What’s the News: You might already know that sperm, which can survive for only a few hours when exposed to the outside world, can live for several days in women after ejaculation. But did you know that an ant queen can fertilize her eggs with sperm she’s stored for up to 30 years? And that organisms as diverse as birds, reptiles, and insects can hang onto sperm and keep it fresh for days, weeks, or months?
Scientists studying this ability have been trying to figure out how females do it, and in a recent paper, researchers put forth evidence showing that the ladies may be arresting the aging process, by slowing down sperms’ metabolism.
What’s the News: In the squid world, the body size of male spear squid determines the mating strategies they use. Small male squid, which have no chance of physically competing with their larger rivals, must try to get with the females of the species on the sly. Now, researchers in Tokyo have learned that this difference in mating behavior has resulted in the evolution of divergent sperm types, though perhaps not in the way you’d think: diminutive male squid actually produce larger sperm than big male squid.
What’s the News: Researchers at Kyoto University in Japan have created fully functioning sperm from mouse embryonic stem cells. The sperm cells were able to fertilize mouse eggs in vitro, and when the scientists implanted the embryos into surrogate mothers, the mice gave birth to healthy offspring. The research, published in the journal Cell, may someday help treat infertility in humans.
What’s the News: What if the egg is fine and the sperm is dandy, but you still can’t seem to have a baby? Couples who are having trouble conceiving can testify to the frustration of learning that there’s no clear reason for their infertility. Now, however, scientists have found a genetic mutation that makes outwardly normal sperm much less fertile, potentially explaining many such cases and suggesting new routes to conception.
What’s the News: For the first time in medical history, scientists have successfully grown mouse sperm in a laboratory. As Northwestern University cell biologist Erwin Goldberg told New Scientist, “People have been trying to do this for years.” It’s hoped that being able to grow sperm outside the testes will lead to improved fertility treatments for men.
How the Heck:
Not So Fast:
Next Up: This technique still needs to be proved in humans, and if it is, it could have wide-ranging effects. For example, in the future, doctors might be able to extract testicular tissue from young boys—who haven’t yet developed mature sperm—and then grow sperm in the lab. Or for infertile men, doctors could extract germ cells, produce sperm, and then find out what’s wrong with them.
Reference: “In vitro production of functional sperm in cultured neonatal mouse testes” Takuya Sato et al. doi:10.1038/nature09850
Image: Wikimedia Commons / Bobjgalindo
A new study of 218 Chinese men found that even low levels of the controversial plastics chemical bisphenol A (BPA) can lower sperm quality and count.
For the study, which was published in the journal Fertility and Sterility, researchers noted the participants’ sperm quality and urine BPA levels over five years. When compared to participants without detectable levels of the chemical, men with BPA in their urine were three times more likely to have low quality sperm.
“This adds additional human evidence that BPA is bad,” said [the study's first author] De-Kun Li…. “The general public should probably try to avoid exposure to BPA as much as they can.” [Washington Post]
That’s a tough order, because BPA is all over the place. It’s found in everything from sports equipment to medical devices to the plastic lining in canned foods.
Li’s previous studies have shown sexual effects of high levels of BPA, including inducing impotence in male factory workers exposed to it. Those studies were done with men exposed to about 50 times as much BPA as the average U.S. man, so the results might not apply to your average Joe.
Dear male reader: Just so you know, your sperm isn’t that different from a sea anemone’s.
Sperm is so vital, a new study in PLoS Genetics found, that one of the genes responsible for it hasn’t changed in 600 million years. Insects, humans, marine invertebrates, other mammals, even fish—the males of all these creatures share a common sperm gene that dates back to before all those animals diverged all those millions of years ago, according to the team led by Eugene Xu.
From an evolutionary point of view, that longevity is simply stunning.
“It’s really surprising because sperm production gets pounded by natural selection,” Xu said. “It tends to change due to strong selective pressures for sperm-specific genes to evolve. There is extra pressure to be a super male to improve reproductive success. This is the one sex-specific element that didn’t change across species. This must be so important that it can’t change” [MSNBC].
We mentioned on Monday that Bill Gates was giving $300,000 to a geoengineering scheme that would shoot seawater skyward to seed clouds. But the billionaire doesn’t just wanted to save the planet and stop the AIDS crisis—he would also like to improve your sex life.
The Bill & Melinda Gates Foundation funded 78 promising but offbeat projects this week, one of those gifts being $100,000 to James Tsuruta and Paul Dayton of the University of North Carolina to pursue their idea of using ultrasound as a temporary and reversible male contraceptive.
Ultrasound produces a mild heating that appears to disable sperm cells and deplete the supply of stem cells that are required to replenish sperm reserves in the testes. Post-treatment images of the rat testes showed the tubules inside the testes completely lacking in sperm with almost no immature stem cells [The Times].
In leafcutter ants and honeybees, it’s survival of the fittest sperm. Biologist Boris Baer, for a study out this week in Science, investigated these two species because of their peculiar sexual practices: In one day, the queen acquires all the sperm she’ll need to fertilize her eggs over the course of her lifetime. But in the race to be the top genetics-spreader, the males have evolved a dirty trick. Their seminal fluids actually do battle within the female’s reproductive tract.
To test out the idea, Baer and colleagues exposed the sperm of the bee and ant males to their own seminal fluid, and also to that of other males of the same species. The seminal fluid killed more than 50 per cent of the rival sperm within 15 minutes. “The males seemed to use the seminal fluid to harm the sperm,” says Baer [New Scientist]. When the team studied other organisms whose lifestyle didn’t depend on this kind of polyandry, they didn’t see the same effect.