Artificial tail-less sperm is the best test-tube sex cell yet

They can’t swim. But artificial mouse cells that resemble nearly mature sperm are the best test-tube sperm cells yet, meeting the elusive gold standard set in 2014.

The cells resemble spermatids, the round cells that mature to form the familiar tailed sperm. Generated from embryonic stem cells, Jiahao Sha of Nanjing Medical University in China and his team have shown that, when injected using a method used in some forms of IVF, these cells can fertilise mouse eggs, and go on to produce pups that themselves grow up to be fertile.

These artificial spermatids are the first in vitro sex cells to meet a set of criteria defined by three fertility and reproduction researchers in 2014. The guidelines were intended to add rigour to the race to artificially generate sperm-like cells, an endeavour that is heating up worldwide.

Unlike many other efforts, Sha’s cells successfully undergo the meiotic cell divisions that are crucial for making genetically correct sex cells. Until now, researchers have struggled to prove that they have pushed cells through an important but complicated dividing process that leaves cells with only half of the father’s chromosomes. “We think our work is the first to monitor and examine all requirements for successful meiosis,” says Sha.

But Sha’s team haven’t won the race yet. They generated their spermatids from stem cells taken from mouse embryos. While embryonic stem cells are easily available in laboratory mice studies, they cannot be taken from infertile adult men, meaning this particular technique couldn’t be used as a fertility treatment.