Mind the gap please!
Nanoscale tubular interconnections between plant cells, called plasmodesmata, have been recognised for some time. But it is only fairly recently that similar connections have been observed between animal cells (Rustom et al, Science, vol 303, p 1007). Since that landmark paper, these “tunneling nanotubes” or membrane nanotubes, as some researchers term them, have been observed in a number of different types of tissues. At first their function was not clear but a number of studies are now casting light on their function between cells.
Unlike gap junctions between cells which have a channel of around 0.5nm to 2nm, just large enough for ions and very small molecules, membrane nanotubes are between 50nm and 200nm in diameter with a channel large enough for proteins and many biomolecules, and even cell organelles, to pass through. They can also span distances of several cell diameters, passing round obstacles between cells.
University of Pittsburg researchers have suggested that the membrane nanotubes may be a route for signalling between dendritic cells as part of the immune system recognition of toxins and infective agents. A team at the University of Frankfurt has observed nanotube interconnections between heart cells and progenitor cells in culture and suggest a transfer via the nanotubes of signalling molecules and transcription factors that may have a role in transforming the progenitor cells. Another team at the University of
Western Australia has recently observed nanotube interconnections between dendritic cells in mouse corneas.
However, the nanotubes may also have a role in allowing disease to propagate. Researchers at Imperial College have observed labelled protein moving from HIV-infected cells to health cells along the nanotubes. A study by the US National Institutes of Health suggests that the nanotubes may have a role in transmission of prion diseases between cells. More recently, prostate cancer cells have been observed passing material from one to another though membrane nanotubes.
Full story in the New Scientist.
Posted: November 24th, 2008 under Nanomedicine.
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