Researchers from Shanghai Jiao Tong University have succeeded in growing mice from only paternal DNA. The embryos were created by the merging of two sperm cells, instead of a sperm and an egg. Usually such embryos with parents of one gender die very quickly, but the Chinese discovered a way to bypass that. Their studies appeared on Monday In the scientific journal Pnas.
Animals with only fathers do not exist in nature. Sometimes it happens that mother animals get young with only their own genetic material. This phenomenon is called Parthenogenesis and occurs with certain insects, fish, reptiles and amphibians. The egg is not fertilized, but still grows into an embryo with two sets of chromosomes. Normally one such set comes from the father and one of the mother. In fact, there is something going wrong with Parthenogenesis: the cell mechanism that normally stops that development from one parent does not do his work. For the genetic diversity – and therefore the resilience – of posterity, it is usually better if there are two different parents. But sometimes Parthenogenesis is evolutionary, for example in the absence of partners.
On and off of genes
That controlling cell mechanism is based on so-called epigenetics: the on and off of specific genes. This happens thanks to certain molecular groups that may or may not ‘join’ the DNA, so that a gene can or cannot be read. The epigenetics sends, among other things, which cells grow to which tissues.
“In earlier studies we have already succeeded in growing from two haploid stem cells – stem cells, each with only one set of DNA – embryos and even adult mice,” says Bart Gadella, researcher in veterinary medicine at Utrecht University. He specializes in reproductive biology, and was not involved in current research. “The new thing about the Chinese study is that DNA was used from sperm cells of two different mouse men.”
Also new is that the Chinese have successfully taken over the so -called ‘epigenetic control’ of the melted cells, Gadella continues. The Chinese have identified seven regions that together ensure that possibly melted male – or female – gender cells do not grow into an embryo. They have epigenetically modified those regions with the CRISPR-Cas cutting and sticking technique, so that embryos could grow with only fathers.
Three-parenting
“But note: here is actually three-parentembryos,” Gadella notes. “The researchers first removed the Celkern DNA from egg cells of female mice. Then they injected the DNA of two sperm heads of two different male mice.” But in the mitochondria, the ‘energy factories’ of the egg, there was still mitochondrial DNA of the parent mouse.
A total of 259 in this way fertilized egg cells were then placed in the womb of eighteen female mice. Sixteen of them were actually pregnant and three living male boy were born from this, one of which died quickly. The remaining two ‘androgenic’ (only born of fathers) mice grew up, grew up and then even got healthy offspring.
“Making such androgenic mice is very inefficient,” Gadella notes. “This is more about finding out how the epigenetics sends the male and female sex cells, and why two male or two female sex cells normally do not lead to descendants.”
In people and in other animals there are all kinds of epigenetic abnormalities that can occur in the early embryo and that may be the basis of infertility or miscarriage. Gadella: “By gaining more insights into what is taking place in the epigenom, and being able to recover with such” epigenoom editing, “we may eventually develop treatments against certain forms of infertility.”
The scientific value now lies mainly in gathering knowledge, and not in producing animals – or people – with only fathers. “If this technique is already allowed in humans in the future, then you could use it to conceive children with genetic properties of two fathers,” said Gadella. “The mitochondria and the egg-without-cell core are from a mother. And a surrogate mother will also be needed. But this technique will first have to become more efficient and absolutely safer before we can start thinking that direction at all.”