Call it Human Biology 101: a man’s sperm encounters a woman’s egg, conception occurs, and nine months or so later, a baby is born. However, researchers may have just found a new way to create a baby without an egg, potentially opening the door for male couples to have a biological child and paving the way for new infertility treatments.
The study comes from Dr. Tony Perry and other scientists at the Department of Biology and Biochemistry at the University of Bath, the University of Regensburg, and the Fraunhofer Institute for Toxicology and Experimental Medicine in Germany. The researchers published their results September 13th in the journal Nature Communications. Although the prevailing wisdom is that sperm are too specialized to trigger development without an egg, the researchers challenged this idea by creating a mouse embryo using sperm and no egg.
The researchers started with parthenogenotes, which are embryos created by treating an egg cell with certain chemicals, containing one set of the mother’s chromosomes. Although these cells were created originally by tricking an oocyte, which is an egg cell, into dividing, they are not the same as egg cells and lack the ability to develop as a normal embryo. Usually these embryos die off within a few days because they need to have been fertilized with sperm to signal certain stages of development. In the current study, the researchers injected these embryos made of only egg-origin cells with sperm, after the cells had already divided. The sperm were able to re-program the non-viable egg cells to develop normally, producing baby mice with a 24 percent success rate, with 30 out of 104 embryos surviving. This is compared to the zero percent success rate if the egg-origin cells kept dividing on their own and died off. The baby mice had two sets of chromosomes, one set from the modified egg cells and one set from the sperm.
Scientists had thought that since sperm are so specialized, only an oocyte, an egg cell, could reprogram the sperm to allow an embryo to develop to term. However, the current research suggests that sperm can actually reprogram the non-egg cells to reach full-term development. Although the baby mice seem to be as healthy as their normally-conceived peers, their DNA has been affected by different epigenetic marks, which are signals to tell genes to switch on or off.
The research seems to overturn previous conceptions about reproduction, so to speak. It seems that sperm have the ability to create new life without an oocyte, opening up future possibilities in fertility treatments.
Since the sperm were able to reprogram the parthenogenotes, which could not reproduce on their own, the researchers speculate the same methods could one day create an embryo from skin cells. This could help breed endangered species even when only males are alive, such as in the case of the Galapagos tortoise Lonesome George. The research could also mean that even if a potential mother does not have viable oocytes, for example if they were destroyed during cancer treatments, scientists could one day create an embryo with her skin cells and her husband’s sperm. Another possible use of the technique is creating a biological child from two gay men, giving them both the opportunity to be a biological father, just like a heterosexual couple.
The researchers do caution that these possible uses of their research may be years away. Although the sperm were able to fertilize cells that were not exactly normal egg cells, those cells do differ from normal cells in the body such as skin cells. So, the same techniques used in this research would not necessarily work on skin cells. As well, the sperm fertilized cells that only had one set of chromosomes, while skin cells already have two sets of chromosomes. For the embryo to develop normally, it would need two sets of chromosomes total, not the three sets that would result from combining sperm with skin cells. Researchers would need to find a way to separate one set of chromosomes in the skin cells. Although this may be far in the future, the research does open up possibilities for future fertility treatments.
A woman may experience infertility after surgery, chemotherapy, or radiation therapy for cancer has damaged her eggs. A woman is born with her lifetime supply of eggs, so once those eggs are gone, she does not have the ability to produce her own biological child and must instead rely on egg donors. If scientists could develop a way to produce an embryo from a woman’s skin cells, it would allow her to have a biological child of her own, even if she has no eggs.