Researchers at the University of Pennsylvania School of Veterinary Medicine have derived uniparental embryonic stem cells - created from a single donor's eggs or two sperm - and, for the first time, successfully used them to repopulate a damaged organ with healthy cells in adult mice.
Their findings demonstrate that single-parent stem cells can proliferate normally in an adult organ and could provide a less controversial alternative to the therapeutic cloning of embryonic stem cells.
"Creating uniparental embryonic stem cells is actually much more efficient than generating embryonic stem cells by cloning," said K. John McLaughlin, an assistant professor in Penn's Department of Animal Biology and researcher at the Center for Animal Transgenesis and Germ Cell Research at Penn's New Bolton Center. "The fact that we are not destroying a viable embryo in the process also avoids certain ethical issues that currently surround embryonic stem cell science."
McLaughlin and his colleagues report their findings in the journal Genes & Development.
"While previous research has approached the possibility of using a woman's egg cells to create therapeutic stem cells, we discovered that we could actually repopulate an adult organ. To our surprise we also found that by using male-only derived embryonic stem cells, we could do the same," McLaughlin said. "In humans, this could provide a therapeutic route for both genders; members of either sex can use this technique to produce compatible stem cells, much like you might donate blood for your own use in advance of an operation."
Parthenogenesis, the act of creating an embryo without fertilization, is common in some plants, insects and animals, including the recent and celebrated case of the "virgin birth" of a komodo dragon in England. Humans and all other mammals, however, require two sets of chromosomes - one from each parent - to create a functioning embryo.According to McLaughlin, this is because mammalian embryos rely on a process called genomic imprinting, where cells will read certain genes from only one parent. Imprinting failures could lead to the death of an embryo and are frequently associated with some forms of cancer and other genetic disorders.
"There was considerable doubt that uniparental stem cells would work since the lack a balanced set of chromosomes from both parents would interfere with the natural outcomes of genomic imprinting," McLaughlin said. "It turns out that genomic imprinting may be more a concern for developing stages and not so much a factor in the routine function of adult tissue, which was the ultimate goal for deriving these stem cells."