Still needs an egg

Healthy mice have been created using sperm and cells that aren’t quite eggs for the first time. New Scientist questions whether this really brings us any closer to making babies with two biological fathers.

What happened in the experiment?

Toro Suzuki at the University of Bath, UK and his team combined sperm with non-egg cells to produce 30 mouse pups that then went on to have healthy offspring themselves. But there are a few caveats. To do this, they created 104 embryos, only 30 of which survived. And they didn’t use just any old cell – they generated special types of cell by exposing eggs to a certain chemical.

So they just used sperm and eggs?


Those were the starting points, yes. But instead of using eggs, they used cells that were made by tricking egg cells into dividing – eggs would never normally do this, until after they had been fertilised.

They then managed to fertilise these daughter cells with sperm cells, and found that these cells then divided. When this happened, some of the cells produced contained one set each of the mother and father’s chromosomes – just like a normal dividing embryo. In this way, some of the fertilized daughter cells generated multicellular embryos that went on to become mouse pups.

Isn’t using an egg cheating?

Team-member Tony Perry, at the University of Bath, UK, says that the key here is that the chemically-induced daughter cells are very different types of cell to the eggs that they came from. Unlike normal egg cells, they can divide to form new cells, which Perry says makes them more like other cells in the body, like skin.

What’s exciting about that?

It raises the possibility of so-called “two-dad babies” – children born using sperm from one man, and some kind of other cell derived from a second man. For a fertilised egg to divide and form an embryo, it also needs to reprogram the genes of the sperm. The cells used by Perry and colleagues were able to do this – the first time a cell other than a natural egg has achieved this.

Will this technique work with other cells?

Probably not – Perry himself says the prospect of using a man’s cells in this way are remote. “This is all very speculative and none of it is possible today, and may never be possible,” says Perry.

The problem is that the special cells they made by manipulating eggs are still very unlike normal body cells in a number of ways. These cells are much bigger than other cells, and it may prove impossible to reprogram their epigenetics to allow them to become embryos.

Another problem is that a man’s skin cell, for example, contains two sets of chromosomes, but sex cells need to contain only one set if they are to produce a healthy embryo. “On top of that there are a whole host of unknown unknowns,” says Perry.

So is this discovery useful in any way?

It’s unlikely to pave the way to embryos with two fathers any time soon, but the experiment has told us something particularly interesting: there is more than one path to a healthy embryo. When the team analysed genes activity as these embryos were developing, they found that the activity was different from what you would normally see in embryos made by eggs and sperm. Nevertheless, the embryos produced healthy pups. A better understanding of how this is possible could provide new insights and treatments for infertility, says Perry.

Journal reference: Nature Communications, DOI: 10.1038/ncomms12676

Read more: Human sperm grown in a lab for the first time, claims study