The time that “evolution” has had to do all its creation of the machinery of life has been constant for over a century. Since around the year 1900 it has been the consensus that the earth is several billion years old. Before then it was variously argued at around a hundred million years by some, eternal by others, and just thousands of years by yet others. Back in Darwin’s day, when life at the simplest level was thought to be just blobs of protoplasm, “evolution” didn’t have such a big job to do. A hundred million years seemed adequate. Today we know that life isn’t blobs of protoplasm at the scale of single cells but in fact each of them is such a complex network of interdependent machines and codes it makes the US space shuttle, all its launch facilities, and all the engineering and manufacturing and support that makes it possible look like child’s play in comparison. Indeed, with every passing day we discover that life is more complex that we thought just the day before. Yet the time for evolution to perform all these miraculous inventions isn’t increasing. Here’s something discovered on one of those recent days that caught my attention:
18 November 2008
by Anil Ananthaswamy
HAD Amin Rustom not messed up, he would not have stumbled upon one of the biggest discoveries in biology of recent times. It all began in 2000, when he saw something strange under his microscope. A very long, thin tube had formed between two of the rat cells that he was studying. It looked like nothing he had ever seen before.
His supervisor, Hans-Hermann Gerdes, asked him to repeat the experiment. Rustom did, and saw nothing unusual. When Gerdes grilled him, Rustom admitted that the first time around he had not followed the standard protocol of swapping the liquid in which the cells were growing between observations. Gerdes made him redo the experiment, mistakes and all, and there they were again: long, delicate connections between cells. This was something new – a previously unknown way in which animal cells can communicate with each other.
Gerdes and Rustom, then at Heidelberg University in Germany, called the connections tunnelling nanotubes. Aware that they might be onto something significant, the duo slogged away to produce convincing evidence and eventually published a landmark paper in 2004 (Science, vol 303, p 1007).
A mere curiosity?
At the time, it was not clear whether these structures were anything more than a curiosity seen only in peculiar circumstances. Since their pioneering paper appeared, however, other groups have started finding nanotubes in all sorts of places, from nerve cells to heart cells. And far from being a mere curiosity, they seem to play a major role in anything from how our immune system responds to attacks to how damaged muscle is repaired after a heart attack.
They can also be hijacked: nanotubes may provide HIV with a network of secret tunnels that allow it to evade the immune system, while some cancers could be using nanotubes to subvert chemotherapy. Simply put, tunnelling nanotubes appear to be everywhere, in sickness and in health.
“The field is very hot,” says Gerdes, now at the University of Bergen in Norway.
It has long been known that the interiors of neighbouring plant cells are sometimes directly connected by a network of nanotubular connections called plasmodesmata. However, nothing like them had ever been seen in animals. Animal cells were thought to communicate almost entirely by releasing chemicals that can be detected by receptors on the surface of other cells. This kind of communication can be very specific – nerve cells can extend over a metre to make connections with other cells – but it does not involve direct connections between the interiors of cells.
The closest animal equivalents to plasmodesmata were thought to be gap junctions, which are like hollow rivets joining the membranes of adjacent cells. A channel through the middle of each gap junction directly connects the cell interiors, but the channel is very narrow – just 0.5 to 2 nanometres wide – and so only allows ions and small molecules to pass from one cell to another.
Nanotubes are something different. They are 50 to 200 nanometres thick, which is more than wide enough to allow proteins to pass through. What’s more, they can span distances of several cell diameters, wiggling around obstacles to connect the insides of two cells some distance apart. “This gives the organism a new way to communicate very selectively over long range,” says Gerdes.
It is a previously unknown way in which cells can communicate over a distance
Soon after they first saw nanotubes in rat cells, he and Rustom saw them forming between human kidney cells too. Using video microscopy, they watched adjacent cells reach out to each other with antenna-like projections, establish contact and then build the tubular connections. The connections were not just between pairs of cells. Cells can send out several nanotubes, forming an intricate and transient network of linked cells lasting anything from minutes to hours. Using fluorescent proteins, the team also discovered that relatively large cellular structures, or organelles, could move from one cell to another through the nanotubes.
Read the whole article here.
The money shot for us is the last section titled (my emphasis below the title):
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.”