[News] Tunnelling nanotubes: Life's secret network

[Michaelangelica]

Tunnelling nanotubes: Life's secret network

If tunnelling nanotubes really are ubiquitous, the critics ask, how come they managed to evade discovery until so recently? And why have they only been seen in cells grown outside the body?

Elusive structures

 

There may be several reasons why nanotubes have eluded notice for so long. For starters, they are extremely fragile: merely shaking a dish of cells or changing the medium - as Rustom failed to do - can rupture these tubes, as can certain chemicals used to fix cells for observation, including those used with electron microscopes.

Even prolonged exposure to light can destroy them. (This extraordinary susceptibility to chemicals and light may one day provide a means to selectively destroy nanotubes.)

 

In addition, when biologists observe cells in culture, they usually focus on the bottom of the dish or slide, where delicate structures such as nanotubes will be obscured by debris. Finally, although nanotubes are elusive, many researchers have spotted them over the years without realising it.

 

At the University of Western Australia in Crawley, for example, Paul McMenamin's team has been studying dendritic cells in mouse corneas.

McMenamin's graduate student Holly Chinnery kept seeing something unusual. "She kept noticing these cells with big, long processes," says McMenamin. "She'd show me the pictures, and I'd say, 'Gosh, I haven't seen anything like that before'." And so it went until a colleague told Chinnery about nanotubes.

"That immediately set us off," says McMenamin. "We realised that we had the first evidence of them in vivo."

Unbelievable

 

Their work, published in May, shows that nanotubes are not just an artefact of the methods used to grow cells in culture, as some have suggested. And what they have seen is spectacular: some of the longest tunnelling nanotubes ever observed, more than 300 micrometres long, connecting dendritic cells in the cornea (The Journal of Immunology, vol 180, p 5779). "We can see them their whole course, spindling all the way through the cornea," says McMenamin. "It's fantastic."

 

"I'll bet you that within weeks to months, people will start noticing them in other tissues. It's just a case of how you look," he adds. "You've got to know what you are looking for. It's a bit like being a good bird-watcher. A hundred people will see a flock of seagulls, and it's only a very good bird-watcher who will spot this one tern flying in that flock."

 

Gerdes, meanwhile, continues to marvel at what is unravelling before his very eyes. "Whatever one can think of has been done by nature," he says. "It is unbelievable what the cell is able to do."

Tunnelling nanotubes: Life's secret network - life - 18 November 2008 - New Scientist