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Japanese researchers report online today in Human Reproduction that mice genetically engineered to carry genes from two females lived nearly 30% longer than mice who carry genes from one female and one male. Females of many mammalian species, including humans, typically live longer than males, although the reason for increased female longevity is unclear.
Manabu Kawahara of Saga University and Tomohiro Kono of the Tokyo University of Agriculture created 13 "bi-maternal" mice by taking an egg from a newborn mouse, manipulating the genes to behave as if they came from sperm, and transplanting that genetic material into unfertilized mouse egg taken from another female. The resulting embryo was then implanted into a surrogate to grow until birth. 13 mice were also obtained through normal breeding methods as a control group.
The control and bi-maternal mice lived in identical, sterile environments. The bi-maternal mice weighed approximately one-third less than the control mice and were significantly smaller in appearance. The bi-maternal mice also lived 842 days on average, 186 days longer than the control group average. The difference in longevity is not likely from genetic causes, as all the mice were very closely genetically related. The authors believe that epigenetic factors associated with sperm, which cause chemical modifications of genes, may account for the difference. They have identified one gene responsible for postnatal growth, Ras-GRF1, that is less active in the bi-maternal mice, although a number of genes are likely responsible for the discrepancies between the two groups.
This result is consistent with male mammals evolving larger bodies to increase their chances of reproducing at the cost of shorter life span and females tendency to conserve resources and energy for the delivering and raising off-spring. "The experiment is simple, and the results are clear, and the difference in longevity is just amazing," says Hiroyuki Sasaki, geneticist and molecular biologist at Japan's National Institute of Genetics. "What's really significant is that this shows the importance of epigenetics." [Human Reproduction, Science]
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