Men, your semen know how heavy you are. A new study reveals that sperm carry chemical tags on their DNA as their owner is skinny or obese. The results suggest that men may be able to provide information on the availability of food in their environment down to their offspring, which could affect the chances of being overweight for their child.
The new data are preliminary but provocative, says Wolf Reik, who studies epigenetics the Babraham Institute in Cambridge, UK, but was not involved in this work. It is the first time anyone has identified changes in these chemical tags called-epigenetic changes in sperm of obese men, he said. But the small number of subjects, he notes, and these studies are always complicated by genetic differences between subjects. It is also notoriously difficult to show exactly how epigenetic changes in sperm or eggs affect the development.
The observations correspond with evidence from a number of studies that have shown that the body weight of parents has long-term effects on the offspring. Mothers who were pregnant during a famine in 1944 in the Netherlands, for example, were more likely to have children and grandchildren-prone to heart disease, diabetes and obesity. Female mice that are malnourished during pregnancy and give birth to puppies that are more likely to develop diabetes and their male offspring have epigenetic changes in sperm. The offspring of these men are also prone to diabetes. Male rats are overfed, when mated with healthy females also had descendants who were prone to developing diabetes. Connections sense of evolution, because it could be an advantage to report the next generation if food is abundant or scarce.
Romain Barres, who studies the genetics of metabolism at the University of Copenhagen, wanted to see if this was evidence of epigenetic changes in human sperm. He and his colleagues collected semen samples from 13 men who were "lean", with a median body mass index (BMI) of 23 and 10 men who were obese, with a median BMI of 32. (A man who is 180 cm and weighs 75 kg has a BMI of 23. Someone of the same height with a BMI of 32 weighs 104 kilograms-229 pounds.) They then examined various epigenetic markers in sperm.
The reasons of a type of molecule that influences epigenetic inheritance, called Small Non-coding RNA, differed between the two groups, such as methylation patterns in sperm DNA in both groups, reports the team today in the Cell Metabolism . Gene methylation, also called imprinting, to determine whether a gene is activated or deactivated. The researchers found more than 9,000 genes that were more or less likely to be methylated according to the subject was thin or obese. Most genes were linked to the development of the brain control of appetite and metabolism.
Changes in genes related to the development and functioning of the brain are particularly intriguing, said Barres. "Brain function is a very important variable in terms of obesity." He also noted that other studies have shown that obese men have a higher risk of having children with disorders of the spectrum of autism. the methylation differences between thin and obese groups were consistent with those found in a recent study of methylation changes in the sperm of fathers who had more than one child with an autism spectrum disorder.
to see if losing weight would affect sperm epigenetic markers, the researchers collected semen samples from six men who were about to undergo surgery for gastric bypass surgery. They then collected samples of a week after the surgery, and a year later. They found differences in DNA methylation genes in 1509 just a week after surgery, suggesting that epigenetic changes can occur quickly. "This means that it is very dynamic," said Barres. A year later, when the weight of men was stabilized, the team found changes in genes 3910. Approximately 40% of these genes were also found to be modified in the study comparing obese and thin men.
Gilean McVean, who studies statistical genetics at the University of Oxford University in the UK, said much stronger data is necessary to argue that nutritional signals are transmitted by epigenetics. obese men were lean and very probably different epigenetic patterns in all tissues throughout the body, he said, including semen. "What differences in sperm have functional consequences for children, "he wrote in an email," is an entirely different matter "
Fixed, December 3, 3:37 p.m.. history has been updated to correct the name of the journal publishing the document. It is Cell Metabolism not Molecular Cell .
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