Artificial sperm with enough male genes to successfully fertilize eggs has been mass produced for the first time.
Scientists in China used the sperm, which does not have a tail and cannot swim, to produce what they call “half-cloned” mice. They say the technique could help speed up research on diseases, such as cancer, by producing large numbers of genetically modified animals.
However, they added it is still too early for the sperm to be used in humans as it still leads to 80 per cent of the offspring dying.
Professor Li Jinson, lead scientist on the project at the Shanghai Institute for Biological Sciences at the Chinese Academy of Sciences, told the South China Morning Post: “Our man-made sperm cells can be used to generate an army of half-cloned mice with ease and efficiency.”
“These half-cloned mice will fight on the frontline in battles against cancer and other genetic health issues. A 20 per cent rate for healthy breeds may be good enough for experimental animals, but not humans. If it is applied to human sperm it could lead to an 80 per cent death rate or defects at birth.”
While man-made sperm has been produced previously by scientists around the world they were previously grown from stem cells.
This method is controversial because it uses cells taken directly from embryos. Professor Li and his colleagues, whose research is published in the journal Cell Stem Cell, have been developing a technique that does not require the destruction of embryos. In 2012 they announced they had placed a sperm into an empty egg, which had had its nucleus and genetic material removed. This turned into an embryonic-like stem cell with functions similar to sperm but without a tail or the ability to swim. These could be used to grow large numbers of these artificial cells.
However, the technique was highly inefficient and eggs fertilised by these artificial sperm cells would only lead to healthy animals around two per cent of the time.
In their latest research, the scientists used a gene editing technique known as CRISPR-Cas9 to alter some of the genes within the artificial sperm. By turning off two genes – H19 and Gtl2 – thought to play a role in embryonic development, they found they could increase the efficiency of the process.
Put simply, they remove the nucleus from an egg, inject the head of a sperm into it and grow it into stem cells, then inject these cells into a healthy egg. And around 20 per cent of the offspring produced using this tweaked artificial sperm survive.
However, they cautioned that they are still investigating whether the editing would have an impact on future generations of animals. Professor Li also said any attempts to use the technique in humans would produce an “ethical crisis.” Instead they claim the technique could provide a way to produce genetically modified animals for studying disease in a laboratory. Writing in Cell Stem Cell, the researchers said: “We hope that the method we have developed will facilitate genetic analysis of development and modelling of diseases in mice.”