Healthy Offspring Created Without Female Egg
The achievement in mice, could pave the way for new fertility treatments, including a way for gay men to conceive children.
In a scientific first, full term development of healthy babies has just been achieved in mice by injecting mouse sperm into non-egg cells, according to new research that has future implications for breeding endangered species and for human fertility treatments, including those that could allow gay male couples to have their own biological children.
The discovery, reported in the journal Nature Communications, challenges two centuries of dogma -- originating at around 1827, when early embryologists first observed mammal eggs -- claiming that only an egg cell is capable of reprogramming sperm to permit the development of a mammal embryo.
Ironically, the new research that could empower men builds on a phenomenon known as parthenogenesis, aka "virgin birth," which has been documented in a number of species, such as certain fish, reptiles, insects and amphibians, but not in mammals. When such births occur, an embryo develops from an unfertilized egg cell, allowing females to reproduce without males.
Previously, scientists were able to "trick" mammal eggs into developing into embryos without fertilization, but the resulting embryos -- called parthenogenotes -- died after a few days in the lab because key processes requiring input from sperm did not happen.
For the recent study, scientists overcame this problem by developing a method of injecting mouse parthenogenotes (which consist of mitotic cells, meaning cells that divide to form two identical cells) with sperm (which is a differentiated, or specialized, cell). The outcome resulted in healthy baby mice, with a success rate of about 24 percent.
"This work shows for the first time that a mitotic cell can completely reprogram a differentiated cell, with the outcome being the birth of live young," senior author Anthony Perry, a molecular embryologist at the University of Bath, told Discovery News. "Yes, the cells are special -- a parthenogenote and a sperm -- but imagine if any mitotic cell could reprogram a sperm in the same way. Then there would be no need for eggs."
"This could revolutionize reproduction," he added. "It would pave the way for gay men to have children; enable oncofertility (fertility among cancer survivors); allow older women, and others with insufficient eggs, to conceive; allow males to self-fertilize, and females (to self-fertilize too) when combined with other technologies," and more, including easier breeding of endangered species "if eggs are difficult to obtain."
For now, mammal males -- including men -- still need females for reproduction and vice versa because, even for this research, the parthenogenetic mice embryos were produced from eggs contributed by females, and females carried the pregnancies to term.
Many unknowns still exist. It's not clear how sperm are able to be reprogrammed to allow for embryonic development with an egg cell, much less without one, as for the new process.
WATCH:What Exactly Happens When Sperm Meets Egg?
What is clear, however, is that the argument that parthenogenotes are more morally acceptable sources of embryonic stem cells is flawed.
As Perry explained, "it has been argued that since parthenogenotes cannot develop to term, they could be a preferred source of embryonic stem cells on ethical grounds, as no embryo is being destroyed that might otherwise have been able to develop to term. Our findings suggest that this assumption may not always be correct."
Yet another challenge to traditional thought concerns the DNA of the baby mice that were born as a result of the new technique.
The DNA of these young mice started out with different epigenetic signatures -- heritable changes in gene expression that do not involve changes to the underlying DNA sequence -- compared with babies born as a result of normal fertilization. This suggests that different epigenetic pathways can lead to the same developmental destination, something not previously shown by scientists.
Commenting on the new findings, Paul Colville-Nash of the Medical Research Council in the U.K., said, "This is an exciting piece of research, which may help us to understand more about how human life begins and what controls the viability of embryos, mechanisms which may be important in fertility."
Both he and Perry think that the research's implications for treating infertility are definitely foreseeable, but are some months, and maybe even years, away.
"The possibilities are in the future," Perry said, "but I think that when they happen, they will be traced back to the work that we have just described."