ESHRE logoHere’s one interesting piece of news. From our early days what we have probably known is the mix of genes from both the mother and the father for procreation. However a new research by experts in Japan found that female mice on an average lived longer than males when the paternal genes were left out. It suggests that female mice produced from genetic material of two mothers alone lived considerably longer.

The researchers reveal that their findings indicate a shorter lifespan for mice that were developed using the normal mix of maternal and paternal genes. On the contrary female mice created by using genetic material from two mothers but no father appear to live significantly longer. This offers the first evidence that sperm genes may be damaging to the lifespan in mammals.

Investigators discovered that mice developed from two female genomes namely bi-maternal (BM) mice lived 186 days longer than the control mice. The normal combination of a male and female genome was used to create the control mice. The mice used in this analysis were claimed to have an average lifespan of around 600-700 days.

The distinct research was conducted by Professor Tomohiro Kono (PhD), from the Department of Bioscience, 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). They are of the opinion that a gene on chromosome 9 related with post-natal growth could possible be the reason for the dissimilarity in longevity.

Prof Kono commented, “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.”

Prof Kono and Dr Kawahara set out to analyze the lifespan of mice produced without sperm to gain more information about the difference. Non-growing oocytes (eggs) from day-old mice were collected and their genetic material was manipulated for this purpose. The genes were tuned to behave like sperm genes, following which they were transplanted into the fully grown, unfertilized oocytes of adult mice that had their nuclei removed (enucleated oocytes).

Later these reconstructed oocytes progressed into embryos after which they were moved into surrogate mother mice. Bi-maternal mice having genetic material from two mothers, but no father were the outcome of this.
For control mice, natural mating that was genetically identical to the BM mice was used. They were developed in a normal manner with genes from male and female mice.

Between October 2005 and March 2006, 13 BM mice and 13 control mice were born. The researchers found that the average lifespan of BM mice was 841.5 days versus 655.5 days of the control mice. 996 days was apparently the longest time that any of the control mice lived. All but one of them appeared to have died by 800 days. The longest time alive for the BM mice on the other hand was 1045 days. All but three of them supposedly lived for more than 800 days.

The weight of the mice was checked at 49 days and 600 days around i.e. 20 months after birth. The researchers discovered that the BM mice were significantly lighter and smaller as compared to the control mice. Along with considerable surge in one type of white blood cell, eosinophil, the immune system of the BM mice was also better. Infection-free environments, with free access to food were provided to both sets of mice. This ruled out the possibility of external environmental factor playing a part in the difference in life spans.

“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,” mentioned Prof Kono.

The researcher concluded that the study could give an answer to the basic questions like if longevity in mammals was controlled by the genome composition of only one or both parents. It could also explain why women may be at an advantage over men as far as lifespan is considered.

The research is published online reproductive medicine journal Human Reproduction.