What is a model organism?
When you think of animals used in research, mice and guinea pigs probably come to mind first.
You may picture researchers testing a drug’s efficacy or examining structures in these animals before moving on to actual clinical trials.
That picture isn’t wrong, but there are many other organisms used in research.
Medaka, zebrafish, nematodes, E. coli, yeast, Drosophila melanogaster, the African clawed frog, Arabidopsis thaliana, the silkworm, and so on…
These organisms are called model organisms, and a wide range of research is carried out with them.
A model organism is a species that the research community studies exhaustively, so that by coming to know it inside and out we can understand features and principles shared with other organisms.
What is Drosophila melanogaster?
Some of the organisms on that list may surprise you, but Drosophila melanogaster is probably the odd one out.
Wait, a fly? The kind that shows up in your kitchen?
Exactly!
The scientific name of this fruit fly is Drosophila melanogaster.
It has featured in a number of Nobel Prize–winning studies and is used widely in research.
Besides the Japan Drosophila Research Conference (JDRC), where fly researchers gather, there are fly meetings in the United States, Europe, and Asia, along with conferences focused on the fly nervous system such as NeuroFly and Neurobiology of Drosophila—research is happening on a global scale.
The advantages of working with flies include:
・they have a central nervous system
・a rich set of genetic tools
・the existence of balancer chromosomes
・a short generation time
・ease of rearing
・stereotyped behavioral patterns
and many more.
Because researchers around the world all study Drosophila melanogaster, enormous databases have been built up, and in the brain nearly the entire network of neuron-to-neuron connections is now known.
At this point you might wonder whether there is anything left to study. It’s true that we know the wiring, but in many cases we still don’t know what function that wiring serves.
On top of that, in areas such as immunity and developmental patterning, there remain a huge number of open questions, including which molecules are involved.
You might ask what all this effort is for—but it is precisely by going this far that we can uncover principles universal to living things!
That is what a model organism is.
And these mechanisms can be applied to drug development, safe genetic engineering, and more.
A brief history of Drosophila research
The story goes that it all began in 1901, when a well-known figure (Charles W. Woodworth) recommended the fly to someone (William Ernest Castle) as a material for genetics.
The reason: it was easy to rear in large numbers.
Later, Thomas Hunt Morgan became famous for his genetic studies using Drosophila. His discovery of mutants and his demonstration that genes reside on chromosomes had an enormous impact on genetics.
Another landmark was the discovery of the homeotic genes, which have a major influence on development.
Drosophila work also played a major role in the discovery of clock genes.
Being rearable in large numbers, being an insect, and allowing mutants to be generated easily were advantages no other organism offered, which is exactly why the fly was such an outstanding material for genetic research.
Today, applications of the GAL4/UAS system, balancer chromosomes, and a wide variety of other tools have all been developed.
A few extra notes
In labs that study Drosophila, the flies are kept in cylindrical containers called vials, about 3 cm in diameter and 10 cm tall.
Most labs have a dedicated fly room where large numbers of these vials are stored.
Some people worry that flies must be dirty, but their food is a jelly-like medium containing yeast—not raw meat or anything like that—so bacteria don’t proliferate.
They are fairly hardy and relatively easy to rear.
That is probably why they have been studied for so long.
Dissections are done by hand with forceps under a stereomicroscope.
We dissect flies that are only about 2.5 mm long using forceps.
Behavioral experiments are also possible, and all sorts of research is done with cleverly designed apparatus.
Another wonderful thing about flies is that there are stock centers in several places around the world, holding large numbers of fly lines carrying specific genetic manipulations created in labs elsewhere, from which you can obtain whatever strain you need.
That means you don’t have to build fly lines yourself and can start experiments right away.
(Making a genetic manipulation yourself takes at least three months.)
Truly standing on the shoulders of giants.
Biologists often say that once you start working on Drosophila you can never work on anything else—a testament to just how well suited the fly is to research.