Fly on the Wall

Making fly science approachable for everyone

Category: Fly Life

Fly Life: Fruit flies in the science classroom

Do you remember sitting in the science classroom in grade school, looking at pictures of pea plants to learn about inheritance? What if you could have tested Gregor Mendel’s theories of inheritance yourself (without watching plants grow)?

Well, you can! As it turns out, fruit flies are a great teaching resource for the science classroom. They are cheap, easy to maintain and store, and are well-understood, since they’ve been studied by researchers for over a century. These characteristics allow teachers to set up hands-on experiments for their students, and quickly adapt to students’ curiosity-driven questions.

Fruit flies can be used for teaching a variety of scientific concepts, from genetics to behavior, and the related experiments can be engaging, fun, and easy to understand. I want to talk about some of my favorite examples (some of which have gone from science fair projects to published peer-reviewed articles!).

Inheritance and Evolution

Punnet square for red- and white-eyed fliesAn example of a punnet square for mating a white-eyed and red-eyed fly. The white eye is caused by a sex-linked recessive genetic mutation. Male offspring have white eyes because they only have one copy of the gene (the mutation) from the white-eyed “mother”, while female offspring have a backup normal “red” copy inherited from the “father”.

Do you remember doing the punnet squares for Mendel’s pea plants? Punnet squares are diagrams used to predict what traits offspring will inherit from two different parents, and is the most common way to teach inheritance in the classroom. Fruit flies, with their short lifespan and quick generation time (offspring are available in only two weeks!), are perfect for a hands-on version of this experiment. Flies with different traits (such as red eyes and white eyes, or curly wings and straight wings) can be mated. While waiting for the next generation, students can predict what percentage of the offspring will have each trait. Two weeks later, they can sort the flies to test their predictions.

UNC’s The Wonderful Fruit Fly website is great for seeing how punnet square experiments can be performed with fruit flies.

Red- vs white-eyed fliesThe fly on the top has a mutation that causes white eyes. The fly on the bottom has normal red eyes. source

Another great example for an experiment was described in an article published in the journal Evolution. Because multiple generations of fruit flies can be studied in a matter of months, students can actually see evolution “in action”. In the published example, students added a single red-eyed fly to a large population of white-eyed flies. Flies with white eyes have poor eyesight and are less healthy than flies with red eyes. Over the course of the experiment, students watched as the healthier red-eye gene spread through the population, simulating the way a random advantageous mutation in nature can spread via natural selection.

This is only a couple of the dozens of interesting genetic experiments that can be performed in class. For more examples, the Tree of Life web project site is a great resource. 

Behavior and Health

Dyed food experimentFlies that eat dyed food have colored abdomens. Image modified from Isono and Morita, 2010.

Although fruit flies are most commonly associated with genetics experiments, they can also be used for behavioral experiments. One of my favorite examples is testing flies for food preference, in which students can give a group of flies a choice between two or more food sources, and count the number of flies that land on each. To make it even more interesting, the food can be dyed different colors. Once ingested, the dye is visible through the flies’ abdomens, allowing students to count how many flies have chosen each food based on color. Wouldn’t it be cool to see blue and purple flies under a microscope?!

Food preference experiments from middle school science fairs have actually made the news a couple of times over the past two years. In 2013, student Ria Chhabra developed an experiment to test whether organic food really is better than conventional food. She raised flies on each type, and found that flies raised with organic foods lived longer and healthier lives. The results were published in the peer-reviewed scientific journal PLoS One.

A similar story was released in 2014, when student Simon Kaschock-Marenda wondered whether fruit flies would like artificial sweeteners as much as normal sugar. He raised flies on sugar and several different sweeteners, including Truvia. His results, also published in PLoS One, showed that erythritol, the main ingredient of Truvia, was actually toxic to fruit flies.

These two heartwarming stories demonstrate how fruit flies can be used in the classroom to inspire students to pursue curiosity-driven science.

Want to start using flies in your classroom? There are many resources available online for experiment ideas, as well as “How-to” guides for setting up and maintaining a fly lab. One of the most comprehensive is the “How-to Fly Manual” from the researchers at the University of Manchester’s Fly Facility.  Another great resource is the “Drosophila Melanogaster in the classroom” blog, which details how to set up a classroom using fruit flies.  

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Many thanks to my friend Brittney for her help with resources and ideas for this post, gathered from her own volunteer experiences teaching fruit fly science to eager young minds.

I would also like to thank Dr. Andreas Prokop at the University of Manchester for some of the resources and inspiration for this post.  He and other fly researchers at the University of Manchester maintain an impressive array of lay information about fruit fly research and resources on their website (not just about how flies can be used in the classroom, but also how flies can be used to conduct high-quality research in disadvantaged regions and countries, where resources and funds may be limited).

 

Fly Life: Watching fruit flies sleep

Did you know that fruit flies sleep? There are actually a lot of similarities between sleep in fruit flies and sleep in humans and other mammals. For example…

Caffeinated flyImage modified from Colwell, 2007
  • Like us, fruit flies get most of their sleep at night, and they also have an afternoon slump (although unlike us, they actually give in to their sleep desires instead of running for coffee).
  • Their sleep is affected by the same drugs: caffeine, cocaine, and modafinil (an alertness drug) keep them awake, while antihistamines (allergy medication) make them drowsy just like us.
  • They sleep more at higher temperatures (think of lazy summer days)
  • If they get a bad night’s sleep, they’ll try to sleep more the next day to make up for it. In fact, sleep deprivation even affects their memory performance (have you ever noticed that your memory isn’t so great after a bad night’s sleep?)

And the comparisons don’t stop there. Over the years, fruit flies have proven to be a great animal model for studying sleep, and researchers have used them to improve our understanding of why sleep is important. In fact, earlier this year a group of researchers found that young flies need sleep for normal brain development.

But, how do fly researchers actually study sleep in these tiny flies?

DAM system

The most common method is called the Drosophila Activity Monitoring (DAM) system. Flies are loaded into individual tubes (Figures A-C) and placed in a DAM machine (Figure D). An infrared beam (marked as a red line in Figure D) crosses each fly tube, and the machine notes when the beam is blocked by the fly. If the beam isn’t broken for five or more minutes (meaning the fly hasn’t moved), it’s counted as sleep. Using this method, researchers can analyze how long a fly sleeps, how many times it goes to sleep and wakes back up (called sleep bouts) and the duration of each sleep bout.

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DAM system in incubatorClick here for a larger version of the picture

To conduct the sleep experiment, the machines are hooked up to a computer and placed in an incubator, which controls the humidity, temperature, and lights. The light cycle is usually set to lights-on for 12 hours (day) and then lights-off for 12 hours (night), and experiments often run for several days or even weeks. In this picture, a newer version of DAM machines is shown (one is circled in red).

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Sleepless dataSleepless mutants sleep much less than normal (control) flies. Image modified from Koh et al, 2008

This system allows researchers to study the sleep habits of dozens of flies at once, and it’s relatively quick and easy (compared to studying sleep in mammals). So what’s an example of a real sleep experiment? In 2008, the Seghal lab used this system to find sleep-related genes. They ran a genetic screen in which they exposed a population of flies to toxic chemicals that caused random mutations in their DNA. Then, they tested the flies to see if any had sleep abnormalities. They found that flies with a mutation in one gene (which they aptly named sleepless) slept about 80% less! Isn’t it crazy that a single gene can affect such a complex behavior so dramatically?

Sleepless dataA common way to display fly sleep habits over the day and night period for one day. The amount of sleep within 30 minute intervals (y axis) is plotted for the time of day (x axis). Note that Sleepless mutants (open circles) sleep much less than control flies (filled circles). The bar at the bottom indicates time: white = day, black = night. Image modified from Koh et al, 2008

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In another experiment that same year, the Guo lab was interested in finding out how sleep affects memory. They tested the sleeping habits of a fly mutant called amnesiac, which can’t form long-term memories. They found that amnesiac mutants had very fragmented sleep (meaning that they woke up a lot during the night). The fact that the same gene is involved in both sleep and memory provides a link that researchers can use for future studies about how these behaviors are connected.

Tracker setupA schematic of the Tracker setup. Image modified from Gilestro, 2012

Although studies have shown that the DAM system is relatively accurate for measuring fly sleep, more sophisticated methods have recently been developed for tracking fly movement. These systems (sometimes called the “Tracker” program) rely on cameras and sensitive tracking software to measure movement at a much higher resolution. As use of the Tracker program becomes more widespread, I have no doubt that we will gain yet more insights into how and why we sleep.

 
 

References:

  • Potdar S. (2013). Lessons From Sleeping Flies: Insights from Drosophila melanogaster on the Neuronal Circuitry and Importance of Sleep , Journal of Neurogenetics, 27 (1-2) 23-42. DOI: http://dx.doi.org/10.3109/01677063.2013.791692
  • Koh K., M. N. Wu, Z. Yue, C. J. Smith & A. Sehgal (2008). Identification of SLEEPLESS, a Sleep-Promoting Factor, Science, 321 (5887) 372-376. DOI: http://dx.doi.org/10.1126/science.1155942
  • Liu W., Beika Lu & Aike Guo (2008). amnesiac regulates sleep onset and maintenance in Drosophila melanogaster, Biochemical and Biophysical Research Communications, 372 (4) 798-803. DOI: http://dx.doi.org/10.1016/j.bbrc.2008.05.119
  • Donelson N., Kim E.Z., Slawson J.B., Vecsey C.G., Huber R. & Griffith L.C. (2012). High-resolution positional tracking for long-term analysis of Drosophila sleep and locomotion using the “tracker” program., PloS one, PMID: http://www.ncbi.nlm.nih.gov/pubmed/22615954
  • Gilestro G.F. (2012). Video tracking and analysis of sleep in Drosophila melanogaster, Nature Protocols, 7 (5) 995-1007. DOI: http://dx.doi.org/10.1038/nprot.2012.041

Fly Life: Fruit flies at SFN 2014

Every year, over 30,000 neuroscientists gather at the Society for Neuroscience annual meeting to present their latest research and catch up with long-lost colleagues. This year’s meeting took place November 15-19th at the Walter E. Washington Convention Center in Washington DC. The meeting is often dominated by researchers working with mammalian models (we Drosophila researchers often attend conferences specific to our model instead), but invertebrate scientists still make a good showing every year. And this year’s meeting was a great one for fruit flies!

This year, two of the Special Lectures were dedicated to fruit fly research. First, Dr. Amita Seghal presented her lab’s latest sleep research showing that young flies need more sleep for normal brain development (I reviewed their latest paper). This finding highlights how important it can be for children of all species (including humans) to get enough sleep. Later in the week, Dr. Vivian Budnik presented her lab’s discoveries on the mechanisms neurons use to form stable connections (called synapses) and talked about how problems in these processes in humans can lead to disease.

Fruit fly researchers also presented over 100 posters and gave several short talks on a range of topics, from basic molecular and cellular research to complex behavioral studies, such as how sleep and memory can arise from a network of cells. Although it can sometimes be hard to imagine how fruit fly research could be relevant to humans, research in this animal model often has important implications for human diseases. In particular, fly researchers presented in several sessions related to Alzheimer’s disease this year, and they also showed up in sessions for other human diseases such as schizophrenia, Parkinson’s disease, and autism. In fact, a fly poster about a possible new treatment for a genetic form of autism was highlighted in a SFARI post by blogger Virginia Hughes (also an official blogger for SFN 2014).

Did you see (or present) any fascinating or surprising fruit fly research at SFN this year?  Leave a comment below!

Fly Life: How to name your new fruit fly gene (and what not to name it)

When it comes to genetic research, fruit flies take the spotlight. They are often used to study specific genes, and researchers who find new genes get the privilege of naming them. The best way to study a gene is to mutate it and see what happens when the gene’s function is lost. As a result, genes are usually named after the phenotype caused by the mutation.  For example, one of the genes I work with is amnesiac. As you can probably guess, flies with a mutation in the amnesiac gene can’t form long-term memories!

This naming convention can often be very confusing for first-time fly students. One of the first genes we learn about is the white gene, which codes for eye color. Flies with a normal version of the white gene (usually written as w+ ) actually have red eyes, while flies with a mutation in the white gene ( w– ) have white eyes.

Over the years, fly scientists have amused themselves by choosing hilariously descriptive names for newly discovered genes. Here are some of my favorites (these are real scientific gene names):

  • Cheapdate– mutants have decreased resistance to the effects of alcohol
  • Hangover– mutants can’t develop a tolerance for alcohol
  • Dunce– mutants have learning deficits
  • Tinman– This gene regulates the development of a heart, so flies with a mutation in this gene can’t grow a heart. Named after the character in Wizard of Oz
  • Ken and Barbiemutants do not develop external genitals
  • Swiss cheese mutants have holes in their brain
  • I’m not dead yet mutants live twice as long as normal flies, a reference to Monty Python and the Holy Grail
  • Groucho Marxmutants develop an excess of facial bristles
  • Out Cold mutants lose coordination at cold temperatures
  • Clumsy – mutants have trouble walking

Fly scientists have been getting away with choosing funny (and sometimes politically incorrect) gene names for decades. But over 75% of fruit fly genes are shared with humans, so not only would some of them eventually be found in humans, but they’d also be associated with a genetic disorder. And that’s where fly scientists can get themselves into trouble. For example, several years ago a gene named Hedgehog made headlines when it was found in humans.

The Hedgehog gene was discovered in 1980, and was given its name based on the observation that a mutation in this gene led to spiky-looking larvae. Three versions of this gene were later found in humans, one of which was named Sonic Hedgehog (SHH) after Sega’s video game character. Unfortunately, this gene has since been linked to a human developmental disorder called Holoprosencephaly, in which an SHH mutation leads to severe brain, skull, and facial defects. Doctors soon began to protest having to explain the joke name to patients with extreme medical conditions.

In 2006, the Human Genome Organization Gene Nomenclature Committee stepped in and changed some of the most offensively named genes. Another gene that was targeted was Lunatic Fringe, which was originally given its name because mutant flies had defects on the edges of their wings. In humans, however, mutations in the gene (which was renamed LFNG) leads a hereditary spinal defect called Jarcho-Levin Syndrome.

Michael Jackson flyDrawing by the talented artist at Drosophila Drawings.

But despite these naming blunders, fruit fly research on these genes has and will continue to help in the search for treatments for these genetic disorders.  And fly scientists haven’t stopped taking the opportunity to come up with fun names for newly discovered genes. Earlier this year, the Dickson fly lab published a report on “Moonwalker” flies: flies that couldn’t change direction and were permanently stuck walking backwards.


Video: The left side shows a fly walking normally. The right side shows a “moonwalking” fly unable to walk forwards.

 

 

References:

Fly Life: A day-in-the-life of a fly scientist

… and all you ever wanted to know about fruit flies!

Have you ever wondered how fruit fly scientists perform experiments with these tiny insects every day? Since I work with fruit flies, I want to provide a glimpse of the day-to-day life of a fly researcher (imagine you’re a “fly on the wall” in our lab!). My project is to figure out how neurons in the memory system communicate with each other to store long-term memories. I dissect fruit fly brains and use fluorescence imaging to watch what neurons are doing in real-time, and I collaborate with other graduate students and postdocs in the lab who perform behavioral experiments. But what are the day-to-day activities that every fly scientist has to take care of?
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Incubator filled with fliesOur stocks of flies are kept in incubators at a stable temperature and light cycle.

My day usually doesn’t start until 10am when the lights in our flies’ incubators turn on. Most of our flies are kept in these refrigerator-sized incubators at a tightly-controlled temperature of 25°C (77°F), which is a fruit fly’s favorite temperature. They’re also kept on a strict light cycle—12 hours of light starting at 10am followed by 12 hours of darkness, which is important for reducing variation in behavioral experiments.
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Rack of fly vialsFly lines are kept in vials, which are stored on racks for easy stacking.

There are thousands of different fly lines, but I only have about 200 of them. Each fly line is kept in a small vial with food at the bottom (the yellow stuff, which is a thick gel of yeast, sugar, and cornmeal) and a cotton plug at the top to keep them from escaping. Each fly line has to be “flipped” to a new vial every couple of weeks after the hundreds/thousands of flies have finished making a mess of their current home.
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Close-up of fly vialA fly vial in use.

If you look closely, you can see pupal cases stuck to the walls of the vials. An adult fly can live for about a month at its optimal temperature, during which time a female can lay hundreds of eggs. The eggs hatch into larvae after approximately 24 hours, which spend about 6 days chewing through food and gaining strength. When the time is right, the larvae climb the sides of the vials and turn into pupae. After 4 motionless days, a new

Fruit fly developmentFruit flies go through four life stages: egg, larva, pupa, and adult. source

fly emerges from its pupal case. In total, it takes about 10 days after an egg is laid before a fly emerges. We can tell when a fly is about to come out because the pupa gets darker as the fly develops inside it. Within hours after emerging, an adult female fly is ready to mate and lay eggs.

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Knocking out flies in a vialKnocking out flies with CO2 in the vial prevents them from escaping
Flies on a CO2 padFlies are dumped onto a CO2 pad to keep them unconscious while they are being sorted.

Now I need to get flies out of some of those vials so I can use them for my experiments. Carbon dioxide (CO2) knocks flies unconscious, so we slide a syringe needle in through the cotton top of the vial and pump in some CO2 to knock them out. Then we can dump the flies out onto CO2 pads, which have a porous styrofoam top and CO2 flow underneath to keep the flies unconscious.
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Wild-type vs mutant fly eye colorsWild flies (bottom) have bright red eyes, but lab flies (top) usually have white eyes until a gene with an eye color feature is added. source

For our experiments, we need to make sure our flies have the right genes or mutations. In my case, I need flies with a fluorescent marker in memory-specific regions of the brain so I can see them under a microscope. This usually means I need to collect flies with two added genes in their DNA: a “marker” gene and a “location” gene. I will need to sort through the flies to make sure they have both genes. Luckily, when a scientist makes a fly line with a new gene, they attach some DNA code for a physical feature to the gene. Usually, the feature is a change in the flies’ eye color. Although wild flies have bright red eyes, our lab flies are bred to have a mutation in the eye color gene so that they have white eyes.

Flies with orange eyesLab flies with an extra gene inserted into their DNA usually have orange eyes. The shade of orange varies, but darker colors can often mean more than one new gene is present. Photo by Weiwu Xie, source

Because our flies have no eye color, adding a gene with an eye-color feature makes these flies stand out among their white-eyed brethren. This way, we can sort through the flies and pick out the ones with colored eyes, most commonly orange. Flies with two genes have darker orange eyes because the color adds up, which is great for me.

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Flies on a CO2 padWe use a fine-tipped paintbrush to carefully sort through the flies without harming them.

I sort through the flies under a microscope using a paintbrush, and then brush the flies I need for my experiments into smaller vials to separate them.

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fly morgue“Fly morgues” are used to dispose of flies. They also conveniently double as fly traps.

There are, of course, tons of flies I don’t need. We can’t possibly save all the unnecessary flies, so they get dumped into a “fly morgue”. These are bottles filled with a mixture of water, ethanol, apple cider vinegar, and a drop of dish detergent. The funnel keeps them from escaping after we dump them in, and the detergent breaks the surface tension of the water so the flies can’t just skim across the surface. It’s a quick and painless death for our noble subjects, and at least they die swimming in their beloved vinegar. These also make great traps in the home to take care of fruit fly infestations. If you don’t have any vinegar, a splash of wine should do it.

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Dissection microscopeA dissection microscope. A dish with wells for dissecting is shown underneath.

Now it’s time to prepare the flies for experiments. For some people in our lab, this means loading the live flies into machines that track their activity for sleep or memory studies. For others, such as myself, it means dissecting out the brains from individual flies (or in some studies, the larvae instead), and performing experiments on the brains instead of live animals. As you can imagine, it takes a pretty long time to learn how to dissect out the tiny brain from these insects. We use a microscope to see what we’re doing, and very carefully remove the shell of the fly head using fine-tipped tweezers.

Close-up of fly head during dissectionA close-up “action shot” of a fly head being dissected. The head is being held with a pair of fine-tipped tweezers.

If you’re interested in seeing a dissection in action, check out this video from Jove, the Journal of Visualized Experiments.

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Rendered depiction of adult fly brainA graphical representation of an adult fruit fly brain. Modified from Chiang et al, 2011

The final brain is too small to see by eye (though the most experienced among us can point out the tiny white dot in a drop of water). Fun fact: did you know that fruit flies don’t have blood like we do? They have an open circulatory system filled with “hemolymph”, which is a clear liquid filled

Picture of dissected fly brain in a wellClick on the picture for a bigger version. The brain (circled in red) is floating in a solution. Can you spot it?

with nutrients for cells. We dissect brains in a solution that’s designed to mimic this hemolymph and keep the brain alive as though it was still inside the fly.

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Fluorescence microscope

Close-up of the imaging set-up for dissected fly brains. Fresh hemolymph-like solution is being perfused in from the right to replace the old solution being vacuumed out on the left. A 60x magnification objective is shining a tiny beam of fluorescent light into the dish.

Image of mushroom bodies in dissected brain

A structure in the fly brain called the “mushroom bodies” is fluorescing under a microscope. Photo by Jenett et al / CC-BY-2.0

Once I’ve dissected my brain, I pin it down in a dish for imaging. The brain-in-a-dish is placed under a microscope with a fluorescent light so that the fluorescent marker in the brain glows. During the experiments, I make sure that fresh hemolymph-like solution is flowing over the brain and being vacuumed out on the other side to keep the brain healthy, and sometimes I use this system to add in drugs which can affect activity in the neurons. This allows me to manipulate specific neurons and study how it affects communication between them.

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In future “Fly Life” articles, I will go into detail about how specific experiments are performed, such as my imaging technique or the behavioral experiments used by my labmates. Until then…

Got any questions or want more details? Feel free to ask in the comments section!

Fly Life: Why fruit flies are a good model organism for research

Since this is my first post, I’d like to start by talking about the basics: Why are we doing research with fruit flies, or even animal models in general? How can these simple organisms possibly provide us with relevant data for future human research? Generally speaking, animal models are important for biological research because they allow scientists to reproduce human diseases or abnormal behavior without the ethical concerns inherent in human studies. Although there are obvious differences between humans and other animals, there are many molecular and cellular processes that are shared among all species through evolution. Many complex human behaviors are also seen in animals, such as aggression, circadian rhythms, sleep, learning and memory, and mating. By studying these processes and behaviors in animal models, researchers gain an understanding of the basic biology underlying them and can use this knowledge to figure out how diseases occur when things go awry (and then, how to fix it).

One important feature of an animal model is the ability to manipulate its genome and investigate the function of specific genes. For example, scientists know that a mutation in the Pink1 gene is responsible for early-onset Parkinson’s disease in humans1, but they don’t know what the gene does. Researchers need to know the gene’s function before they can investigate how the mutation leads to Parkinson’s disease and how to treat it. In animal models, researchers can study the gene’s function by manipulating the relevant gene in the animal’s genome. One important type of genetic modification is a gene “knock-out”, which means they induce mutations in a specific gene so that it becomes inactive or non-functional. By observing the resulting change in physiological processes or behavior, researchers can determine what role the gene played in normal functioning. In our example, scientists can knock-out the Pink1 gene in fruit flies or mice and observe on a cellular level which processes fail. As an added benefit, researchers can also observe the animals themselves to see if they display the same behavioral phenotypes as patients with Parkinson’s disease, such as tremors and slow movement.

Another type of genetic manipulation is called a “knock-in”, where researchers instead insert a gene from another animal into the genome (or, in many cases, replace the endogenous gene with another version). For example, researchers often insert a mutated version of a human gene implicated in a disease, which allows them to determine what effect that particular mutation has on the gene’s function. To return to our previous example, scientists can insert the specific human Pink1 mutation that leads to early-onset Parkinson’s disease in an animal’s genome instead of knocking it out completely. It also allows them to test the effectiveness (and side effects) of various promising therapeutic drugs before going to human trials.

So what’s this got to do with fruit flies? On the About page on this site, I gave a few of the basic reasons why Drosophila melanogaster are a good model organism for research. They have been used for research at all levels of biology, but genetic research is where these organisms really shine. Genetic manipulations are so much easier in fruit flies because they have a smaller genome which was fully sequenced in March 20002. Their short life cycle and large number of offspring are also advantageous for genetic research because new fly lines are quick and easy to make. As a result, although the manipulations I mentioned above can be performed in other animal models such as mice, mutations in flies can be generated much more easily. Making a new line of flies usually only takes about six weeks and costs less than $300, whereas a new mouse line takes months and can costs thousands of dollars.

But how do researchers initially identify the genes they’re interested in studying? In order to study a process or behavior using specific gene mutations such as those described above, the gene of interest must already be identified. Traditionally, researchers perform genetic “screens”, in which they use mutagenic chemicals or radiation to cause random mutations in animal models, and then screen offspring for abnormalities of interest and identify the mutated gene. But this process is difficult and time-consuming, and often based on luck. Enter Drosophila melanogaster! Using this animal model, researchers can conduct large-scale screens relatively quickly. For example, to find genes that contribute to sensing heat, fly researchers can test hundreds of mutant flies for impaired heat avoidance within a few months. Identifying those relevant gene(s) will then provide a starting point for studying sensory abnormalities in mammals.

Fly head with green eyesFigure 1. Example of GAL4/UAS system being used to express a green fluorescent marker in eye cells. Photo by Wellcome Images / CC by-nc-nd 2.0

Over the years, fly researchers have also developed an impressive array of genetic tools that make Drosophila melanogaster an even better animal model for research. The list is too long to cover in this post, but there is one type of tool I want to introduce called binary expression systems. These systems allow fly researchers to insert a specific gene into a specific set of cells, and even activate or deactivate the gene at specific times. One example binary expression system is called the GAL4/UAS system. In this system, a fly line with genetic instructions for where something should be inserted (GAL4) is mated with a fly line with genetic instructions for what should be inserted (UAS). For example, the GAL4 instructions might define the cells of the eyes while the UAS might be a green fluorescent marker. The individual lines have no abnormal phenotypes, but the offspring will have green glowing eyes! (Figure 1) In practice, if a researcher wants to know in which brain structures a particular gene is expressed, such as Pink1, they can combine a GAL4 that targets “cells with an active Pink1 gene” with the green UAS. They can then view a dissected fly brain under a microscope and see where cells expressing the Pink1 gene are located in the brain. Alternatively, the UAS instructions might describe a gene to be deactivated instead of inserted, so that it is “knocked out” in a very specific set of cells. In this way, fly researchers can investigate the gene’s function in a relevant region without affecting the overall health of the fly, which is important for reproducing human diseases that target specific cell-types. And because genetic modification is so comparatively easy in the fruit fly, the fly community has created a collection of thousands of fly lines for these systems, which researchers are more than willing to share with each other. As a result, it is often very likely that a specific combination is already available for use.

Ultimately, every animal model has its advantages and disadvantages.  Researchers wouldn’t want to use monkeys for a genetic screen, and they wouldn’t use fruit flies to study complex emotions. But although fruit flies may seem very different from us, an estimated 75% of known human disease genes have a match in the fruit fly genome3-4. They are already being used as a genetic model for several human diseases, including Parkinson’s disease, Alzheimer’s disease, Fragile X syndrome, and Rett’s syndrome, in addition to the basic research needed to advance our general understanding of biology and how we work.  So the next time you see a fruit fly in your kitchen, make sure to say “thank you” before you swat it away.

  1. Valente EM, Salvi S, Ialongo T, Marongiu R, Elia AE, Caputo V, Romito L, Albanese A, Dallapiccola B, & Bentivoglio AR (2004). PINK1 mutations are associated with sporadic early-onset parkinsonism. Annals of neurology, 56 (3), 336-41 PMID: 15349860
  2. Adams MD, Celniker SE, Holt RA, Evans CA, Gocayne JD, Amanatides PG, Scherer SE, Li PW, Hoskins RA, Galle RF, et al (2000). The genome sequence of Drosophila melanogaster. Science (New York, N.Y.), 287 (5461), 2185-95 PMID: 10731132
  3. Reiter LT, Potocki L, Chien S, Gribskov M, & Bier E (2001). A systematic analysis of human disease-associated gene sequences in Drosophila melanogaster. Genome research, 11 (6), 1114-25 PMID: 11381037
  4. Lloyd TE, & Taylor JP (2010). Flightless flies: Drosophila models of neuromuscular disease. Annals of the New York Academy of Sciences, 1184 PMID: 20329357

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