Why females live longer than males: is it due to the father's sperm?

Dec 01, 2009

Researchers in Japan have found that female mice produced by using genetic material from two mothers but no father live significantly longer than mice with the normal mix of maternal and paternal genes. Their findings provide the first evidence that sperm genes may have a detrimental effect on lifespan in mammals.

The research, which is published online today in the journal, found that mice created from two female genomes (bi-maternal (BM) mice) lived an average of 186 days longer than control mice created from the normal combination of a male and female genome. The average lifespan for the type of mice used in the study is between about 600-700 days, meaning that the BM mice lived approximately a third longer than normal.

Professor Tomohiro Kono (PhD), from the Department of , Tokyo University of Agriculture, and Director of the Nodai Research Institute (Tokyo, Japan), and Dr Manabu Kawahara (PhD), associate professor at the Laboratory of Animal Resource Development, Faculty of Agriculture, Saga University (Japan), carried out the research. They believe the reason for the difference in longevity could relate to a gene on chromosome 9 associated with post-natal growth.

Prof Kono said: "We have known for some time that women tend to live longer than men in almost all countries worldwide, and that these sex-related differences in longevity also occur in many other mammalian species. However, the reason for this difference was unclear and, in particular, it was not known whether longevity in mammals was controlled by the genome composition of only one or both parents."

To answer this question, Prof Kono and Dr Kawahara set out to study the of mice produced without sperm. To do this, they collected non-growing oocytes (eggs) from day-old mice, manipulated the in these eggs so that the genes behaved like sperm genes, and then transplanted this manipulated genetic material into the fully grown, unfertilised oocytes of adult mice that had their nuclei removed (enucleated oocytes). These reconstructed oocytes developed into embryos, which were transferred into surrogate mother mice. The mice that were born as a result were bi-maternal, having genetic material from two mothers, but no father.

The researchers created control mice through natural mating that were genetically identical to the BM mice, apart from the fact that they were created in the normal way with genes from male and female mice.

There were 13 BM mice and 13 control mice born between October 2005 and March 2006, and Prof Kono found that the average lifespan was 186 days longer in the BM mice than in the controls (841.5 days versus 655.5 days). The longest time that any of the control mice lived was 996 days, with all but one of them dying by 800 days, while the longest time alive for the BM mice was 1045 days, with all but three of them living for more than 800 days. The researchers checked the weight of the mice at 49 days and 600 days (around 20 months after birth) and found that the BM mice were significantly lighter and smaller than the control mice. The BM mice also seemed to have better immune systems, with a significant increase in one type of white blood cell, eosinophil.

Both sets of mice were kept in the same, infection-free environments, with free access to food, making it unlikely that some external environmental factor was the cause of the difference in life spans.

Prof Kono said: "We believe that the most likely reason for the differences in longevity relates to the repression of a gene called Rasgrf1 in the BM mice. This gene normally expresses from the paternally inherited chromosome and is an imprinted gene on chromosome 9 associated with post-natal growth. Thus far, it's not clear whether Rasgrf1 is definitively associated with mouse longevity, but it is one of the strong candidates for a responsible gene. Furthermore, we cannot eliminate the possibility that other, unknown genes that rely on their paternal inheritance to function normally may be responsible for the extended longevity of the BM mice."

Imprinted genes are genes that are turned on, or "expressed", according to whether they are inherited from the mother or the father.

The researchers write: "Our results are consistent with models based on sex-specific selection of reproductive strategies, e.g. male individuals maximizing fitness by an intense investment in reproduction by way of a larger body size in order to achieve more breeding opportunities, resulting in shorter longevity…. In contrast, female individuals usually do not engage in such costly male behaviours and instead tend to optimize their reproductive output by conserving energy for delivery, providing for offspring, foraging and predator avoidance. Our results further suggested sex differences in longevity originating at the genome level, implying that the sperm genome has a detrimental effect on longevity in mammals."

Prof Kono concluded: "The study may give an answer to the fundamental questions: that is, whether longevity in mammals is controlled by the genome composition of only one or both parents, and just maybe, why women are at an advantage over men with regard to the lifespan."

More information: Longevity in without a father. Human Reproduction journal. doi:10/1093/humrep/dep400

Source: European Society for Human Reproduction and Embryology (news : web)

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User comments : 12

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ArtflDgr
not rated yet Dec 01, 2009
and with socialisms constant ideal of procrustean equality, what would be the solution to such inequity?
Ponchorain
Dec 02, 2009
This comment has been removed by a moderator.
Objectivist
not rated yet Dec 02, 2009
Yes longer lives... but: http://www.youtub...T4Om6JT4
danlgarmstrong
1 / 5 (1) Dec 02, 2009
Wow - I'm not suprised that women have this genetic advantage. But there is another breakthrough totally glossed over - THE GENETIC MATERIAL CAME FROM TWO MOTHERS! Lesbian couples can have kids together! Should'nt be too long before this is offered.
danman5000
not rated yet Dec 02, 2009
The researchers created control mice through natural mating that were genetically identical to the BM mice, apart from the fact that they were created in the normal way with genes from male and female mice.

How can one born from normal male+female genes be genetically identical to one from two females? Unless maybe there were pairs of male+female identical twins?

Another question: Were the BM mice only females? Seems like you couldn't have male offspring from parents with no Y chromosome. That might put a damper on danlgamrstrong's plan above (though they probably hate men anyway so maybe not).
danlgarmstrong
not rated yet Dec 02, 2009
I think that 'genetically identical' mice are special research lines with little or no genetic variation between generations. By definition, identical twins are of one sex, they cannot be a mix. Fraternal twins come from two eggs.

If the lesbian couple wanted a male baby, it might be possible to transplant a Y chromosome for an X. Probably wont happen much, even though lesbians dont necessarily hate men (they just love each other). Turns out that human reproduction is a bit more complicated than that of mice, so it might still be a wait, though I did read something on ScienceDaily about turning skin cells into eggs and sperm.
Objectivist
not rated yet Dec 02, 2009
@danlgarmstrong:

It has already been known and tested for quite some time that this is possible.

@danman500:

That is interesting, and I too wondered about the gender of the test subjects. This seems rather important since the whole article begins by explaining that females tend to live longer than males.

Still if this method only produces female offspring it poses yet another important question: whould you be able to breed a strain of long living mice this way? And afterwards would a single male-female fertilization cancel aquired effects?
CarolinaScotsman
not rated yet Dec 02, 2009
I would point out that the reason women live longer than men is the fact that we men have to live with them, but I suppose that's too simple.
danlgarmstrong
not rated yet Dec 02, 2009
Prof Kono said:We believe that the most likely reason for the differences in longevity relates to the repression of a gene called Rasgrf1 in the BM mice. This gene normally expresses from the paternally inherited chromosome


It sounds like something inherited from males prevents the expression of the Rasgrf1 gene. They still need to identify exactly what that is, so they still need to continue the study.

The study indicates that the artificial 'breeding' of 2 female mice DOES create long lived children. It would be an interesting follow up to check the longevity of those children mated with male mice.

Bswitz
5 / 5 (1) Dec 02, 2009
Male/female procreation yields faster replication and thereby faster evolution. Not to mention an evolutionary stable strategy of competition for mates. Of course now we don't need those advantages, but it is important to note where they derived from.
melajara
not rated yet Dec 02, 2009
Assuming that the BM mice are only females, now another missing information is to know if the CONTROL mice are only females. This condition is mandatory to correlate longevity with gene expression on COMPARABLE (ie same gender) mice.

On the other hand, if the BM mice are a mix of males and females (I doubt it;-) the control group should have exactly the same ratio of males vs females.

Ok, issue solved from reading the original article, available here http://www.oxford...p400.pdf
both groups are comprised of 13 FEMALES :)

For people interested in those type of research especially for their implications for human life extension, have a look at the Mprize here http://www.methus...ion.org/
Truth
not rated yet Dec 02, 2009
I highly agree with Bswitz. Natural evolution generated the male/female combination for a reason, most likey because such a combo has a much higher survival and advancement factor. Otherwise, we'd all be unisex. The vast majority of the advanced living organisms on this planet use the male/female strategy. I believe we seriously need to monitor the long-term results of derailing this time-tested method. We could be shooting ourselves in the foot.
danlgarmstrong
not rated yet Dec 03, 2009
I believe we seriously need to monitor the long-term results of derailing this time-tested method. We could be shooting ourselves in the foot.


I find it odd that many people seem to think that the future will converge on one type of human. I think that technology will provide MANY choices, and people being people we will investigate them all. Long term - there will be a species explosion all steming from the human race. Alternative sexualities will certainly be a part of that.

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