Fatherless mice born
Dr. Kirsty Horsey
Progress Educational Trust
23 April 2004
A mouse 'conceived' from the egg cells of two female parents, with no input from a male sperm cell, has grown into a normal, healthy adult. The Japanese scientists who created the mouse - called Kaguya - believe that this is the first time a mammal has been created in this way. The scientists, from the Tokyo University of Agriculture, created the mouse by combining the DNA from one female mouse egg cell with that of another, having first caused one of the eggs to 'metamorphosise into a surrogate sperm'. Essentially, this means the mouse has two mothers and no father, say the scientists, who published their work in the journal Nature.
The process whereby an egg cell is triggered to develop without having been fertilised by a sperm is known as parthenogenesis. In sexual reproduction, an egg provides only half the chromosomes needed to form an embryo, whereas in parthenogenesis the egg duplicates its own chromosomes to form the full complement. Mammals never normally reproduce in this way, although some reptiles, amphibians, fish, insects and, occasionally, chickens can do so naturally. In 2001, American biotech company Advanced Cell Technology (ACT) caused controversy when it announced that it had created the world's first parthenogenetic embryos, using chemicals to trigger development in an egg cell. And in September 2003, US scientists used parthenogenesis to derive embryonic stem cells from an unfertilised monkey egg.
Mammalian parthenogenetic embryos do not normally survive and develop further because of a process called imprinting - the switching off of certain genes during early embryo development, according to whether they were inherited from the father or mother. But in the new research, the scientists used an immature egg taken from a genetically altered mouse, with changes affecting two imprinted genes called H19 and Igf2. This, they said, gave the modified egg similar genetic qualities to a sperm. They then combined the genetic material of this egg with an egg taken from an 'ordinary' lab mouse. When they analysed the genes in the resulting pups, they found that the mice all appeared to be 'genetically relatively normal'. The researchers conclude that imprinting is the only thing that prevents parthenogenetic reproduction in mice, but surprisingly, manipulating just two imprinted key genes can overcome this natural barrier.
Remaining problems with imprinting could explain why it took the scientists who produced the 'fatherless mouse' nearly 460 attempts to produce only ten live mouse pups, and why only one of the pups, Kaguya, survived to adulthood. It is certainly the reason why the research team and other scientists have said that the method should not be used for reproduction in humans, although it may be a potential way of creating embryonic stem cells without the need to destroy fertilised embryos. Tomohiro Kono, leader of the research team, said 'this is a very complicated thing. So no. Impossible to do this experiment in a human. And I don't want to do it'. Kaguya is now 14 months old and has reproduced naturally; Kono described her as 'very healthy'.
© Copyright Progress Educational Trust
Reproduced with permission from BioNews, an email and online sources of news, information and comment on assisted reproduction and genetics.
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