Hated at home, loved in research: the fruit fly Drosophila is a favourite in many laboratories. Age researcher Mirka Uhlirova from the CECAD excellence cluster is one of the admirers and explains what makes this small model organism so special.
These critters, only two to three millimeters in size and with bright red eyes, swoop down on rotting fruit and leftover food. They do not eat the fruit itself, but prefer the yeasts that decompose it. Each female can lay up to 40 eggs a day, which can turn into new fruit flies within ten days - one reason why flies become a plague so quickly.
Professor Dr. Mirka Uhlirova looks at her pet with different eyes - the fruit fly with the Latin name Drosophila melanogaster. Uhlirova’s field is ageing research at the CECAD excellence cluster. She smiles when asked about the fruit fly: "Drosophila is an ideal organism for research. The animals have wings, legs, complex eyes and internal organs. The genome is completely decoded, we know the genes - and any change in the genome can be observed somewhere in the fly." Furthermore, the animals are very easy to keep. Anyone who has ever had the opportunity to visit a fly farm will immediately recall the smell again. The mash consists mainly of yeast and has a strong odour reminiscent of a brewery.
The breakthrough of the fruit fly as a research object began in 1910, when the American zoologist and geneticist Thomas Hunt Morgan set himself no lesser goal than to refute the theories of Charles Darwin. Unlike Darwin, he did not believe in the principle of natural selection and the assertion of the better adapted organism. Morgan bred Drosophila in complete darkness for countless generations and expected them to lose their instinct to be attracted to light. After these experiments failed, he exposed the flies to various stress factors such as heat or cold and hoped to be able to force mutations. His experiments failed - but ultimately won him the Nobel Prize for Physiology or Medicine in 1933. Morgan suddenly discovered Drosophila with white eyes during the experiment. This mutation, called white (w), was the first change in the genome related to sex, as Morgan was able to show in further experiments.
Fruit flies also suffer from insomnia, jetlag and alcoholism
"It's almost as if the fly was made to help the researchers," said Steve Jones, geneticist and Director of aging research at the Institute für Biology at University College London. In fact, fruit flies and humans share about 60 percent of their genes, 77 percent of the known genes für human diseases have a counterpart in flies. A long, long time ago there was a common ancestor. What it looked like is unclear - but the similarity remains. There are flies that suffer from insomnia, alcoholism can occur, and just like us these animals need time to adjust their "internal clocks" after a time change.
In her laboratory Mirka Uhlirova deals among other things with the human eye disease Retinitis pigmentosa. Three million people worldwide are affected, in Germany probably 30,000 to 40,000. The disease usually occurs in adolescence and begins with increasing night blindness. Gradually, the photoreceptors in the retina are destroyed. In the further process vision decreases further, resulting in tunnel vision and blindness.
To date, 45 genes are known that are related to the disease. If some of these genes are used in the fruit fly, Drosophila also develops an eye disease. Here, research is looking for ways to stop or reverse the disease.
The fruit fly even made it into space
In the meantime, Drosophila has already made it to the ISS space station. Not as a nuisance, but as an object of research in microgravity. Over several generations, the effects of weightlessness on muscle growth, the aging process and the immune system have been investigated. Similar to astronauts, it was found that Drosophila's body defences suffer from space conditions.
Fruit flies are also playing an increasingly important role in personalised medicine. Colorectal cancer is one of the most common cancers worldwide. Professor Ross Cagan (Director of the Center for Personalized Cancer Therapeutics, Icahn School of Medicine, Mount Sinai, New York) has started to decipher the genetic code of his patients' tumors and then uses parts of the genes in fruit flies. Subsequently, various chemotherapies are tested on the animals to find an individually effective drug that promises a higher probability of success. "That's the great thing about Drosophila," says Mirka Uhlirova. "There is hardly any other organism for which we have such a repertoire of tools to adapt it."
Six Nobel Prizes awarded for research on Drosophila
The versatility of Drosophila as a research object is also evident in the Nobel Prizes: a total of six Nobel Prizes are awarded for research based on the fruit fly. Among others, the German researcher Christiane Nüsslein-Volhard received the prize in 1995. At age of 75, she daily visits her office at the Max Planck Institute für Developmental Biology in Tübingen.
Although Uhlirova also appreciates Drosophila as a research object, she would rather be spared from them at home and makes traps. Her tip: a small bowl of red wine and a drop of detergent to reduce the surface tension of the water. But there's one thing she can't help: "I have to take a look into the animals' eyes. Who knows, maybe I'll suddenly see a white one instead of a red one."
And perhaps you, dear readers, will see the "plagues" with different eyes from now on.
1933: Thomas Hunt Morgan investigates the role of chromosomes
1946: Herrmann Joseph Muller uses X-rays to cause mutations
1995: Edward B. Lewis, Christiane Nüsslein-Volhard and Eric F. Wieschaus investigate the genetic control of embryonic development
2004: Richard Axel describes the olfactory receptors and the olfactory system
2011: Jules A. Hoffmann investigates the innate immune response
2017: Jeffrey C. Hall, Michael Rosbash and Michael W. Young discover the molecular mechanisms of circadian rhythm