1 in 7 couples has trouble conceiving—and in 40–50% of cases, the problem is sperm-related, due to either low sperm count (oligospermia), abnormal sperm shape (teratospermia), or poor sperm motility (asthenozoospermia). But hopes for couples struggling with male infertility are on the rise, thanks to recent experiments traversing pretty much uncharted terrain. The breakthrough could justifiably be called a tour de force—and I don’t use that term lightly.

What is this piece of groundbreaking research?

A team of scientists led by Toshihiro Kobayashi of the Institute for Medical Science at Tokyo University immersed rat stem cells in what they describe as a ‘chemical soup’—turning them into sperm cells! They injected these back into the rats’ testes, then injected the mature sperm into eggs. Once the eggs were fertilised (becoming what we refer to as an embryo), they were implanted into  the females. The process is similar to ICSI, perhaps the most common treatment of male infertility in humans. Or in a nutshell, it’s rodent IVF—and the process has already produced several pups! As if that weren’t enough, the pups themselves were fertile—they went on to have pups of their own! That is huge. As any scientist knows, it’s crazy enough to be able to create a fully formed animal in a lab—but an animal that isn’t sterile, and one day will in fact be able to bear offspring of its own?! That’s insane.

It may beg the question of you, though: why the hullabaloo? Why have these experiments made such a splash across the front page of every fertility journal worldwide?

The implications for humans are unprecedented

Up until now, scientists in the lab have only been able to produce germ cells (cells that give rise to sperm and egg cells) in mice. What Kobayashi and his colleagues have shown is that the stem cells extracted from rat embryos can be successfully developed in the lab to produce germ cells, which in turn form sperm cells when implanted into rat testes. “Until recently, we didn’t know enough about how rat germ cells develop to adapt the mouse procedure for rats,” he said. “But now we understand more about what proteins and growth factors are needed to generate the rat germ cells.”

The research is making waves across the scientific community, and no wonder: it could spell the beginning of the end for many male fertility problems. Why? Because it may be possible to create sperm in a lab. Human sperm. ‘All’ that scientists would need to do would be to convert egg cells or men’s skin cells into stem cells, then follow the same process as Kobayashi et al. have adopted over in Tokyo to produce gametes (sex cells). The skin cells would be necessary because embryonic stem cells can’t be taken from men, so scientists wouldn’t be able to replicate the exact same approach to generating sperm when it comes to humans. So what’s their plan? The team are working toward artificial generation of rat egg cells, and hope to unearth the principles of sperm generation shared between rats and mice, which could inform the development of the sperm creation techniques in other mammals. Pigs, sure—but humans, too. Mice and rats are far more similar to each other than either is to humans, so the artificial production of human gametes could still be decades away. “Humans and nonhuman primates have different modes of germ cell development, and a much longer developmental timeline,” says Kotaro Sasaki of Pennsylvania University, “So extrapolating the result to other species might not necessarily be straightforward.” But either way, Kobayashi et al.’s research could unlock truly revolutionary insights into both how human germ cells develop, and why their maturation processes sometimes go awry and cause infertility.