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MOUSE EMBRYO MADE WITHOUT FATHER |
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by BBC.com Scientists have made a female mouse egg grow into an adult without fertilising it with sperm, the journal Nature says. The egg had two sets of chromosomes belonging to the mother, rather than one from the mother and one from the father as in a fertilised embryo. The phenomenon, called parthenogenesis, never occurs naturally in mammals. Some researchers say the procedures may be applied to stem cell research, but the scientists who carried out the work say it would not yet work in humans. Mammal difference Tomohiro Kono and colleagues switched off a key gene in the donor egg which affected imprinting - a barrier to parthenogenesis in mammals. "Insects can reproduce by parthenogenesis. Even chickens can be made to reproduce by parthenogenesis. I wanted to find out why mammals are different," Dr Kono of Tokyo University of Agriculture, Japan, told BBC News Online. The team injected the genetic material from an immature mouse egg into a mature egg with its own set of chromosomes. They then "activated" the combined egg, prompting it to start growing as an embryo. By blocking expression of a gene called H19 in the immature mouse egg, the researchers increased the activity of another gene called Igf2. Igf2 manufactures a protein responsible for regulating growth in the developing foetus. These genes are said to be imprinted. This means that some genes are working in maternal DNA but switched off in paternal DNA, or vice versa - they are unequally expressed. The genetic manipulation carried out by the researchers gave the genes a more paternal character. As a result of this modification, two out of 598 knockout mice made it to full term. Low efficiency "The efficiency of this technique is rather low. So it's not a technique that can be readily adapted for practical purposes," Professor Azim Surani, an expert in imprinting at the University of Cambridge told BBC News Online. One of the surviving mice was used for testing, while another, which the researchers named Kaguya, was allowed to grow into an adult. "To me it is striking that a relatively simple genetic modification, where they took away the gene and its regulatory sequences, allowed these embryos to develop," Marisa Bartolomei, associate professor at the University of Pennsylvania, US, told BBC News Online. "Most of them still failed, but the significance is they did get two viable ones and they also got a significant proportion of them further (in development) than anyone has done before." Dr Kono said he did not think the same technique would work in humans. "This is a very complicated thing. So no. Impossible to do this experiment in a human. And I don't want to do it," he said. However, some researchers said that the procedures could - in theory - have applications in stem cell research. Dr Bartolomei suggested that making embryos without the need for fertilisation might allow researchers to circumvent political and ethical obstacles to using stem cells. Dr Kono also agrees that the technique could be suitable for creating stem cell lines. "I would expect that just because it's parthenogenetic, the public wouldn't discriminate between that and the more traditional way of doing it," said Dr William Colledge of the University of Cambridge. Professor Surani commented: "Parthenogenetic stem cells were made many years ago. This latest procedure is a very complicated one and it's not necessary for stem cell research."
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