No, scientists have not figured out how to make “motherless babies,” nor have they gotten any closer to making an embryo without using an egg cell. A paper published yesterday in Nature Communications sparked a flurry of headlines about futuristic ways to get around the basic formula of “sperm + egg = embryo.” Many stories claimed researchers had moved closer to using a skin cell, for example, instead of an egg cell, to make a baby. That, they said, could make it possible for a gay couple to have a baby by fusing sperm from one man with the skin cell of another.
But those headlines and stories frequently left out a crucial detail: The researchers, led by Tony Perry, an embryologist at the University of Bath in the United Kingdom, most definitely needed egg cells—also called oocytes—to make the mouse pups they described. The egg cells they experimented on were past the typical “use by” date, in that they had been chemically prompted to start dividing. (Usually it is fertilization by sperm that provides that signal.) That meant that they had started to grow into parthenogenotes, an unusual type of early embryo. The cells in parthenogenotes contain only half as many chromosomes as usual—precisely because they start out as an egg that has not been fertilized. When scientists took one cell from a two-cell parthenogenote—roughly half a day after they had tricked the egg to start cell division—and then injected a sperm cell, the combination sometimes went on to develop into a mouse pup. Roughly a quarter of the parthenogenote cell plus sperm cell combinations produced pups, the authors report.
That is mildly interesting to people who study the nitty-gritty of cell division and fertilization—hence the widely reported comment that the work was a “technical tour de force,” obtained by the Science Media Centre (SMC) from Robin Lovell-Badge of the Francis Crick Institute in London and distributed to journalists (see below). But it has nothing to do with the idea of making an embryo without using an egg cell. As most introductory biology textbooks explain, what makes sperm and egg cells able to merge and make a new organism is that they each contain only half as many chromosomes as other cell types. The technical term for this is a haploid cell. (Cells with the usual number of chromosomes are diploid.) Skin cells are definitely not haploid, and no one has come close to figuring out how to make them so.
In addition, the egg cell contains powerful, as yet unknown factors that enable it to direct the first steps of embryo development. Those factors are what drive somatic cell nuclear transfer—better known as cloning—the process that famously led to the creation of Dolly the sheep from a (diploid) mammary gland cell. The new paper shows that enough of the egg cell magic is still present even after it has been tricked into dividing from one cell into two. But it does not reveal what any of those powerful factors are, nor does it suggest how they might be inserted into a skin cell.
For better or worse, egg cells are still irreplaceable.
So, without further ado, the recipe for transforming a modest developmental biology paper into a blockbuster story, as it played out yesterday in the media:
- Take one jargon-filled paper title: “Mice produced by mitotic reprogramming of sperm injected into haploid parthenogenotes”
- Distill its research into more accessible language. Text of Nature Communications press release: Mouse sperm injected into a modified, inactive embryo can generate healthy offspring, shows a paper in Nature Communications. And add a lively headline: “Mouse sperm generate viable offspring without fertilization in an egg“
- Enlist an organization to invite London writers to a press briefing with paper’s authors.
Headline of Science Media Centre press release: “Making embryos from a non-egg cell“
- Have same group distribute a laudatory quote from well-known and respected scientist:
“[It’s] a technical tour de force.”
- Bake for 24 hours and present without additional reporting. Headline in The Telegraph: “Motherless babies possible as scientists create live offspring without need for female egg,” and in The Guardian: “Skin cells might be used instead of eggs to make embryos, scientists say.”
Such headlines appear to have the London-based SMC second-guessing its decision to hold a press briefing on the work. Fiona Fox, SMC director, sent Science the following statement when asked whether it contributed to the hype:
Lovell-Badge says he, too, was dismayed by the press reaction. “I thought Tony’s paper was well-done technically,” he tells Science. But “it doesn’t get us closer to making haploid cells out of diploid ones … [and] it does not say that oocytes are not needed.”
With reporting by Science News Staff.