Science Snaps: a fly on the wall of cancer research

Tiny fruit flies – officially called Drosophila melanogaster – have helped scientists uncover a huge amount about cancer in the lab. And they’re helping Dr Jean-Philippe Parvy, at our Beatson Institute in Glasgow, study how the immune system targets tumours.

“Drosophila is probably the best characterised animal model, and has led to the development of an amazing number of very powerful and versatile genetic tools,” says Parvy.

The genetic code of these flies is simpler than humans’, allowing scientists to tweak the flies’ DNA to understand how different genes work.

Because they’re small, scientists can also keep thousands of flies at a time. And if you’ve ever had a swarm in your kitchen around an overripe banana, you’ll know they reproduce rapidly, which in the lab is great to help study gene changes relatively quickly.

“Despite hundreds of millions of years of independent evolution, around 4 in 5 genes involved in human diseases are present in Drosophila,” Parvy adds.

And while our DNA has several copies of most of these genes, Drosophila often only have one. This makes it easier to study what these genes do by making simple changes to the DNA code and seeing what happens.

All of this makes the humble fruit fly a firm favourite of scientists.

Lard of the flies

“The main goal of our lab is to understand how a tumour interacts with far-away tissues,” says Parvy. “We’re particularly interested in the immune tissues, which in Drosophila includes a tissue called the fat body.”

In his lab they’ve shown that, like in humans, a tumour in Drosophila triggers a strong response from the immune system that, in some cases, can kill cancer cells.

The adult fly’s tissue known as the fat body. It’s the main metabolic organ of the fly, producing fats that are coloured red here. Courtesy of Dr Jean-Philippe Parvy.

“This immune response occurs mainly in the fat body, and also in the trachea – the respiratory system of the fly, which is the equivalent to the circulatory system in mammals,” he says.

But the molecule controlling the anti-tumour effect is unknown. And Parvy’s goal is to find it.

The image above shows a single picture that’s been reflected, much like a photo would reflect in a mirror.

It shows cells from the fat body, which carries out a similar job to that of the liver and fat tissues in mammals.

But in the fly, it’s also one of the main tissues controlling immunity.

The eye-catching small shapes in the image are individual cells, which Parvy has illuminated using different coloured fluorescent molecules.

The edges of each cell appears in blue, and the nuclei of the cells, which carry each cell’s DNA, are white.

Parvy has then stuck fluorescent red tags onto a molecule he thinks might be important for the cancer-fighting immune response. And fluorescent green tags light up the cells in which genetic tinkering has worked.

These tags help the team follow what happens to the molecules that they switch on or off, and see how this affects the cells and the tumour (though only the third image shows cancer cells).

A fly in the treatment

A tumour in an adult fly. Cells of the immune system are shown in green, and dying cells are shown in red. Courtesy of Dr Jean-Philippe Parvy.

“It highlights the amazing power of the approach, since the way we use the techniques only works in Drosophila and only takes a few days to be carried out,” says Parvy.

By using these genetic tricks, he’s able to quickly test lots of possible suspects, and identify the molecule controlling the anti-tumour push.

It’s taken 2 years of sleuthing, but Parvy thinks he’s close to confirming the identity of the cancer-fighting molecule.

And using these tools he’s demonstrated that this molecule produced in the fat body can specifically target tumour cells, while leaving normal ones alone.

“The molecule is also found in mammals, and turned off in some human cancers,” he says. “The next step is to find out if it works the same way in humans.”

Michael