It’s a big day for sperm science. Â In the journal Nature today, scientists from Japan describe how they were able to mature mouse sperm in a petri dish outside of the testis.
The sperm assembly line is a complicated series of steps that takes about two months from start to finish. Â Sperm start off as big, round immature cells called “spermatogonia” whose main job is to multiply. Â At some point, cells decide to turn into full-fledged sperm, becoming cells known as “spermatocytes”. Â A spermatocyte splits into halves, becoming a “spermatid” in a process called meiosis, which will allow its precious genetic cargo ultimatelyÂ to combine with its complementary other half waiting in an egg. Â The spermatid half cells finally transform their shape, growing propellers, outboard motors and egg-digesting caps in becoming “spermatozoa”.
Until now, scientists were unable to get immature sperm cells to grow outside the body into those exquisitely shaped torpedo half cells. Â That’s where Takuya Sato and fellow scientists have succeeded. Â By carefully controlling the conditions for the growing sperm’s bed, these scientists discovered how to make mature sperm outside the body.
The practical implications are enormous. Â Sperm can be frozen before chemotherapy to spare a man’s fertility, but only from an adult man already making mature sperm. Â We don’t yet have a similar way to preserve the future fertility of a boy who has yet to go through puberty, and this discovery may someday allow doctors to freeze a small piece of testis from a boy about to have chemotherapy and then mature his sperm in a petri dish later in his life. Â For men with “maturation arrest“, where the sperm assembly line stops midstream, it might be possible to grow their sperm to completion in a petri dish, and use the grown sperm in in-vitro fertilization.
The distance between Sato and his fellow scientists’ discovery and practical use is not small. Â Men are different than mice, and trying to shepherd science into the doctor’s office always brings unforeseen challenges. Â But this discovery is a big leap for sperm science.