Biologists discover men hurt mutant mtDNA which support the hypothesis of the curse mother -
There is new evidence that the "curse of the mother" - the possibility that mothers can transmit genes to their children hurt their son, but not their daughters. - which is true in animals
such a possibility arises because there are two independent parts of the genome in eukaryotic cells, which are found in plants and animals, and the two are locked in a "race to the molecular arms centered on the conflict" that impacts human health and welfare. the portion of the genome of the lion is located in the cell nucleus. But there is also a secondary part far smaller located in the mitochondria.
According to the generally accepted theory, mitochondria are bacteria in the independent origin who developed ability to use highly toxic oxygen molecules as a source of powerful energy. Eukaryotes lacked this ability, so some of them have found a way to swallow the ancestor of mitochondria without digest - convert to a "endosymbiont," an organism that lives in the body of another organism. Unlike the nuclear genome, which is constructed from a combination of genetic material father and mother, the mitochondrial genome is transmitted exclusively by the mother. Consequently, the male descendants are an evolutionary dead end. While natural selection removes active mutations in mitochondrial DNA (mtDNA) that weaken women, there is no direct mechanism to remove those that weaken men :. A situation that leads to the curse of the mother
Although natural selection removes active mutations in mitochondrial DNA (mtDNA) that weaken women, there is no direct mechanism for removing those weaken men :. the situation makes the curse of the mother can
Now, a team of biologists at Vanderbilt University and Fred Hutchinson Cancer Research Center in Seattle discovered a mutant mtDNA in the fly Drosophila melanogaster that justifies the curse the assumption of the mother animals. It reduces the fertility of male offspring as they age, but have no observable effect on the siblings of women
"in the 20 years since this possibility has been recognized, some mitochondrial mutants have been reported which have deleterious effects on male offspring, "said Maulik Patel, assistant professor of biological sciences at Vanderbilt who led the study," but none convincingly showed that the mutants lacked negative effects on women. Our study is the first to examine in detail the possible effects of mutant males-harm mtDNA on women and we were lucky to find such a mutant which has a negative impact on male offspring without, as far as we can assessing the potential adverse effects on siblings of women. "
discovery is described in a paper published online Aug. 2 in the journal eLife .
the "mothers curse" is one of the most bizarre consequences of natural selection. According to the theory of evolution, mitochondrial DNA (mtDNA) and nuclear DNA are locked in an endless competition. as is accumulated beneficial mutations, then the other is forced to adapt. This is known as the "Red Queen hypothesis. "The name is derived from a statement by the Red Queen in Lewis Carroll's Through the Looking-Glass". ... You have to run, you can do, to keep in the same place "
In plants, which have far more mitochondrial genomes that contain more genes, striking examples of men mitochondria -nuire have already been discovered. the mitochondrial genome in animals is much smaller, however, making it much more difficult to detect mutations by men hurt like.
the experience that ultimately discovered mtDNA mutant male-harm was something of a tour de force took more than four years to complete. the scientists set up 18 independent lines of fruit flies, each consisting of 300 women and 100 men. in 12 these virgin females lines were collected every generation and mated with males of the original strain. the researchers did this for 35 generations (about 70 weeks). in the other six lines females were allowed to mate with the brothers males and sisters of their choice. Throughout this period, researchers flies fitness monitored to determine whether the men were injured.
"Ganesh Miriyala, Aimee Littleton and I spent a year and a half" flies reversal "with no idea whether we would end up with something meaningful," said Patel. Miriyala and Littleton were technicians research at the Hutchinson Center.
Fortunately, when they were made, the researchers found that a single point mutant mtDNA was taken on one of the lines. This produced a single amino acid change in the chemical structure of a subunit of an enzyme called cytochrome C oxidase. the researchers determined that the mutation causes sperm production and motility of male sperm prematurely abandon as they age, but does not appear to have other effects on men or women.
"We were not looking specifically for mutants that affect fertility," said Patel, "but, in retrospect, it is logical . mutants that affect men but not women should be affecting the tissues that are different in men and women. "
Their findings are consistent with a hypothesis that has been advanced to explain an association between a human mtDNA mutant and reduced sperm motility. This mtDNA mutations can be an important factor for male subfertility incurable, known to affect 7-10 percent of men
the researchers also found that the mutant enzyme was sensitive to temperature. Placing the temperature in their cages of four degrees Celsius caused the holders of men become almost completely barren. This allowed scientists to perform an additional experiment to test a second prediction of the curse of the hypothesis of the mother :. That the nuclear genome should develop mechanisms for the physical restoration of men by suppressing the activity of the male-harm mutant mtDNA
They mated females with mtDNA mutant with men a number of different fruit fly strains collected from a number of different places in the world. Then they dosed the fertility of male offspring and were surprised to discover that the nuclear genomes of most of the strains were able to completely restore male fertility.
"The strategy that we used in this study, as well as progress in methods of manipulating mitochondrial genomes, provides us with exciting new opportunities to explore the" dark side "of one of the symbioses oldest and largest in the world. we hope that this will lead to ways of treating mitochondrial diseases, only some of which currently can be treated, and which are inherited from a newborn on 0 and manifest in about one adult in 5000, "said Patel.
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