Dec. 2, 2009 -- Sperm genes may shorten the lifespan of males compared to females, at least in animals, according to Japanese researchers.
The researchers produced female mice by using genetic material from two mothers but no fathers -- and then found these mice, which they call bi-maternal or BM, lived substantially longer than those with the normal mix of genes from one male and one female parent.
The findings, though only in animals, are believed to be the first evidence that the sperm genome -- all its hereditary information -- may adversely affect the lifespan, says researcher Tomohiro Kono, PhD, professor of bioscience at Tokyo University of Agriculture and director of the university's research institute.
The study is published in the journal Human Reproduction.
Longevity Study Details
"We produced the BMs by manipulating one set of egg genes so they behaved more like sperm genes," Kono tells WebMD in an email interview. "Then, we transplanted the manipulated genetic material into a normal unfertilized egg and grew embryos. The embryos developed into adult female mice, bi-maternal."
The researchers then tracked 13 bi-maternal mice and 13 mice born through natural mating but genetically identical to the bi-maternal mice in other ways. The bi-maternal mice lived about a third longer, or 186 days more, than the other mice. The average lifespan of BM mice was 841.5 days, compared to 655.5 for the naturally mated mice.
The longest lifespan of any of the control mice was 996 days, but the longest life span for the BM mice was 1045 days. All but three of the MB mice lived more than 800 days.
Kono terms the differences in lifespan of the bi-maternal mice ''not dramatic but significant."
The body weight was lower in the bi-maternal mice compared with the typically-bred mice at 20 months after birth. And the bi-maternal mice had better immune systems.
Longevity: Why Women May Live Longer Than Men
Kono says the most likely reason for the longevity differences lies in the repression of a gene called Rasgrf1 in the bi-maternal mice. The gene typically is expressed from the paternally inherited chromosome. It's imprinted on chromosome 9 and associated with growth after birth. Imprinted genes are expressed or turned on depending on whether they are inherited from a mother or a father.
Kono says it's not clear whether Rasgrf1 is associated with mouse longevity but would be a strong candidate to be a responsible gene. Other genes that rely on being inherited from the father to be turned on may also explain the extended longevity of the bi-maternal mice, Kono says.
Longevity Study: Second Opinion
Despite the small sample size and other limitations, the study results warrant follow up, says Dietrich Stephan, PhD, a geneticist who is president and CEO of the Ignite Institute for Individualized Health, Herndon, Va., and reviewed the study for WebMD.
''This provocative study provides preliminary evidence that lifespan in mice can be extended based on whether the animal receives its full genetic complement from two female mice, as opposed to the natural situation of half of its genome from a mother and half from a father," Stephan says.