Fruit flies' eyes shrink a little to see

I spy, with my mechanical eye. It seems a simple mechanical change plays a role in sensory perception in fruit flies, and possibly in many other animals, including humans.

The eyes of the common fruit fly (Drosophila melanogaster) contain clusters of light-sensitive cells organised into rods. When light strikes one of these cells, it triggers a series of chemical reactions. These cause a protein called a transient receptor potential (TRP) ion channel to open. When it's open, the TRP allows charged particles to flow into the cell, causing the cell to send a signal to the fly's brain.

TRP channels play a part in sensory perception in many animals, from nematodes to humans. But nobody knew how the chemical signals make the TRP channel open.

Shrinking rods

"Everyone's been looking for years and years at the chemical messengers," says Roger Hardie of the University of Cambridge, UK. A mechanical trigger was never considered. "No one thought to look," he says.

With Kristian Franze, Hardie found that the chemical signals change the surface area of the cell's outer membrane by destroying some of its constituent molecules. When several cells shrink like this, the entire rod contracts by up to 400 nanometres, a margin big enough to be seen with a microscope. "The whole membrane shrinks," says Hardie. "It's like a little muscle twitching."

The membrane contractions happened just after the chemical signals were released, but before the TRP channels opened. That suggests the contractions at least contribute to the channels' opening, perhaps by deforming the TRP protein.

Taste for TRP

TRP channels are common in sensory systems. Humans have 28 different types of TRP: some allow us to taste, some to feel pain, and others are involved in regulating blood pressure. It's possible that similar mechanical changes might control their behaviour as well.

"I can't see why not," says Konstantin Nikolic at Imperial College London. "This is a big family of ion channels," he says. "Other cells with similar mechanisms in place should affect TRP channels in a similar way."

"We certainly can't rule it out," says Hardie. The processes across ion channels are similar, and the enzyme involved is widely distributed, he says.

Scientists recently speculated that a mechanical process controls signalling in the tiny nerve fibres of a type of wasp. Who said the universe isn't clockwork?

Journal reference: Science, DOI: 10.1126/science.122376

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Source: http://feeds.newscientist.com/c/749/f/10897/s/2460aa31/l/0L0Snewscientist0N0Carticle0Cdn223730Efruit0Eflies0Eeyes0Eshrink0Ea0Elittle0Eto0Esee0Bhtml0Dcmpid0FRSS0QNSNS0Q20A120EGLOBAL0Qonline0Enews/story01.htm

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