September 27th, 2022
Written by: Hannah Deutsch
“You’ve heard about some of these pet projects, they really don’t make a whole lot of sense and sometimes these dollars go to projects that have little or nothing to do with the public good. Things like fruit fly research in Paris, France. I kid you not.” -Sarah Palin (2008)
This comment raises an important question: how can we justify studying the fruit fly? Since the early 1900s studying the fruit fly has shaped our understanding of topics including genetics, radiation, development, smell, immune system, and sleep. And, we have barely scratched the surface for what the fruit fly can teach us.
What have we learned?
Studying the fruit fly (scientific name: Drosophila melanogaster) has led to discoveries that have had far-reaching, but often unknown impacts on science and society. Picture a scientific discovery like dropping a pebble into a pond of still water. The still water ripples as other scientists build off the initial discovery. By the end, the ripples dissipate and the origins of the knowledge may be unknown to the people benefitting from the knowledge. What follows is a brief overview of some discoveries made in the fruit fly that have had a significant impact.
Thomas Hunt Morgan is known as the father of fruit fly research. He used fruit flies to better understand genetics and heritability. Morgan was awarded the Nobel Prize in 1933 for his work confirming the chromosome theory of heredity. He found that genes are carried on chromosomes and those genes always exist in the same order – like beads on a string. He also discovered a concept called crossing over, a process that increases genetic diversity. Think of the beads on the string: crossing over is when you have two strings with slightly different sequences of beads, you then cut the strings in the same place, exchange the strands, and finally tie the new strands together. You end up with two unique strands of beads that are then passed down to offspring, resulting in offspring that have different genetic information than their parents. Thomas Hunt Morgan’s findings still lay the foundation for how scientists go about studying genetics and fruit flies.
There have been a total of six Nobel Prizes awarded for fruit fly research. In addition to the 1933 prize awarded to Thomas Hunt Morgan, in 1946, a prize was awarded for discovering that X-ray radiation results in genetic mutations. In 1995, for understanding how genes control how embryos develop. In 2011, for understanding how the immune system gets turned on. And finally in 2017, for discovering how our sleep/wake cycle is regulated.
These discoveries have impacted not only their specific fields, but also served as the foundation for breakthroughs in other fields. For instance, the 1946 prize for discovering that X-rays lead to genetic mutations resulted in the development of a methodology still used to this day: the forward genetic screen. In a forward genetic screen, scientists randomly mutate the genes of multiple animals, determine if any behave or look different, and ultimately isolate the gene responsible for those differences. This technique led to an explosion in understanding the functions of individual genes and was the basis for the technique used to discover the gene responsible for Cystic fibrosis1. For the world at large, understanding that radiation leads to mutations was critical to protecting us and our environment when using radioactive materials.
While we may not recognize that the pebble that led to all these discoveries was research done with fruit flies, the ripples have been invaluable.
What can we learn?
While we have learned a lot using the fruit fly, we have barely scratched the surface. Fruit flies are an ideal organism to gain more knowledge as they are both easy to use and there are a wide variety of fruit fly tools available to aid in discovery.
Ease of Study
Fruit flies are easy to care for and have striking similarities to humans on a genetic level. The simplicity of fruit fly care is due to the fact that the flies take up very little space, they produce a lot of offspring, and have a short life cycle (10-14 days from breeding to new adults). This enables scientists to house and produce thousands of flies in a small space very quickly. In addition to their practical simplicity, fruit flies are also genetically simple: they have only 4 chromosomes, while humans have 23. Additionally, fruit flies and humans have much in common genetically: we share approximately 60% of our DNA and 75% of human disease-causing genes2 with fruit flies. In humans, scientists run studies to find genetic mutations linked to disease, but end up with too many candidates, many of which are dead ends. Because flies reproduce so rapidly and in such large quantities, it is possible to screen lots of mutations quickly to identify which are worth pursuing. This screening process in flies has made research in diseases including Alzheimer’s Disease, Parkinson’s Disease, and Autism Spectrum Disorder both faster and easier.
Tools
Because fruit flies are so easy to study and people have been studying them for over a hundred years, there are many readily available resources of information and tools.
The massive amount of existing knowledge on fruit flies is incredibly valuable to scientists. The fully sequenced fly genome3 is publicly available and came before the fully sequenced human genome. Additionally, there are ongoing projects expanding on and summarizing what scientists know about the fruit fly including creating a map of every neuronal connection4. This map has already been finished in another model organism, the worm (C. elegans), and is a valuable tool as it allows scientists to know which neurons communicate directly with other neurons (read more about C. elegans here).
Genetic tools are some of the most powerful in fruit fly research. Genetic tools allow scientists to manipulate the fruit fly to test hypotheses about how genes impact behaviors and diseases. For instance, the most popular and well-known fruit fly genetic tool is called the GAL4-UAS system, which enables scientists to express a chosen gene in a group of cells they select. In practice, the GAL4-UAS system can be used to visualize cells, activate or inhibit neurons, or even visualize the activity of neurons as depicted in Video 1.
Since scientists are able to rely on existing knowledge and strong genetic tools when studying the fruit fly, they can ask more complex questions than in other organisms where this infrastructure is not as strong. This is why scientists feel confident that researching fruit flies still has a lot to teach us.
Why study the fruit fly?
When you drop a pebble into still water the ripples inevitably dissipate and the people that come after don’t see the evidence that you were there. This is often the case with science: people are unaware of the origins of the knowledge from which they are benefiting. This is what causes people to ask: why study the fruit fly? And now we know the answer: because those flies on the wall have already taught us a lot that has led to the advancement of science and society and they still have a lot to teach us.
Want to learn more about what we have learned from fruit flies? Read this!
References
3. Adams, M. D. et al. The genome sequence of Drosophila melanogaster. Science 287, 2185–2195 (2000).
4. Hulse, B. K. et al. A connectome of the Drosophila central complex reveals network motifs suitable for flexible navigation and context-dependent action selection. doi:10.1101/2020.12.08.413955.
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