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Honeybees throw light on diet and gene expression |
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Research leader Dr Ryszard Maleszka works in the lab |
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If only the ugly stepmother in Snow White had studied genetic science she might have learned there is an easier way to become queen, well that's if you are a bee. According to scientists at the Australian National University (ANU), becoming the queen bee may be determined by genetics and what is eaten. The truth is, every bee in a hive originally shares an identical genotype, but their growing 'environment' is cleverly crafted by the colony to generate desired outcomes.
Dr Ryszard Maleszka from the ANU's Research School of Biological Sciences said that for honeybees a diet rich in royal jelly causes a genetic switch in young larvae that determines whether they'll become a queen, or live a life of drudgery as a common worker bee.
"Previous research has identified that when a honeybee colony needs a queen, a hatchling is isolated and fed solely royal jelly, eventually becoming a queen," Ryszard explained.
However, the mechanism of how royal jelly modulates the genes of the honeybee to turn it into the queen has until now, been unknown.
"Our research has discovered for the first time that royal jelly decreases the expression of DNA methyltransferase (Dnmt3), an enzyme that drives a process called DNA methylation whereby small chemical tags are added to DNA," said Ryszard.
"Because these tags do not alter the sequence of the letters in the DNA code, but provide an effective way of controlling gene expression, this mechanism is called epigenetic, or 'above the genome' regulation. Epigenetic processes provide a way for environmental factors to affect gene activity. Nutrition, exposure to toxins, and other exogenetic mechanisms can all be potentially involved in epigenetic activity.
"When we silenced the expression of Dnmt3 in young honeybee larvae we found that these individuals developed into fertile queens, whereas the control group yielded workers with no functional ovaries. Thus, silencing Dnmt3-associated DNA methylation mimicked the royal jelly effect suggesting that the fate of young bees is determined by diet-induced epigenetic changes."
According to Ryszard, this is the first time that the process of DNA methylation has been associated with insect development.
"This molecular process is very common in vertebrates and studies in mammals, including humans, suggesting that environmental stimuli such as diet can alter the epigenetic state of the genome and affect gene expression by modifying DNA methylation," he said.
"In addition, strong epidemiological data reveal that cardiovascular and diabetes mortality in children can be influenced by the nutritional status of their parents and grandparents and it is believed that some forms of cancer resulting from smoking affect human DNA at the epigentic level.
"For example, identical twins are also not so identical, especially as they grow older and are exposed different environmental stimuli. Quite often one twin develops schizophrenia or even cancer. Such differences have nothing to do with the twins' identical DNA, but how genes express themselves as a result of chemical modifications in the genes over the years.
"This research will help us to find out more about how an environmental factor such as diet modifies how genes express themselves," Ryszard said.
"Now that we have observed the DNA methylation process in honeybees, which are a much simpler biological model than humans, we have the perfect opportunity to understand more about how this process works in humans."
The key to relating these findings to humans lie in the Dnmts enzyme family. There are three different types of Dnmts which are present in both honeybees and humans. This makes honeybees an ideal organism in which to investigate human diseases and genetics.
"Because all three Dnmt enzymes are shared by humans and honeybees but not by other invertebrate model animals, such findings establish the honeybees as a model to not only study the function of DNA methylation in insects but also for examining fundamental overlaps that may help in understanding the nutritional basis of genetic programming in humans," Ryszard said.
"An example could be to identify how diet can trigger DNA methylation and the development of diabetes in humans despite not having the 'diabetes gene' in their DNA sequence.
"In addition, other diseases such as obesity and heart disease may not have a genetic basis but when the right environmental factors as present, DNA methylation could trigger the development of the disease."
As for the evil step-mother in Snow White, a diet of royal jelly could either turn her into a beautiful queen or possibly bring on a nasty disease. But no doubt, as in all good fairy tales, good will triumph over evil!
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Royal jelly is a thick, creamy and highly concentrated source of proteins, essential amino acids, unusual fats, vitamins, hormones and other nutrients, and is produced by worker bee head glands. It commands premium prices rivalling imported caviar, and is used by some as a dietary supplement and fertility stimulant.
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A honeybee colony generally contains one breeding female, or 'queen'; seasonally up to a few thousand males, or 'drones'; and a large seasonally variable population of sterile female workers.
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Worker bees cooperate to find food and use a pattern of 'dancing' (known as the waggle dance and round dance) to communicate with each other.
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Honeybees perform the dances on return to the hive with the waggle dance indicating that food is further away, while the round dance (a short version of the waggle dance), indicates that food is nearby. Aristotle in 330 BC, described this behaviour in his Historia Animalium. It was thought to attract the attention of other bees. In 1973 Karl von Frisch received the Nobel Prize for decoding the bee dance language.
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There is only one queen per hive. The queen is the only bee with fully developed ovaries and can live for 3-5 years. She lays up to 2000 eggs per day. Fertilized eggs become female (worker bees) and unfertilized eggs become male (drone bees).
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