PLoS Biology: Nanotubes Make Big Science This article reviews work done on TNT's or Tunneling Nanotubes that connect cells that are not in close proximity to each other. It seems to be a mechanism to ensure that cells that need to be together can do so when separated by large distances of up to several cell diameters. To envison developmental biology you have to think like a cell. If you had to connect with a particular cell you could send out diffusible signals but these may not provide the degree of accuracy that you require. In cases requiring greater accuracy, a cell could send out a TNT, connect after utilizing Recognition Factors and then influence the neighboring cell via the transfer of proteins and, apparently, even organelles (see article). One interesting note is that material does not travel within the nanotube--it's not a pipe--but on the surface of the TNT.
A theory created to explain the fact that cancer cells turn back to normal when put in an embryo; it's called the cell recognition theory of cancer. Basically, a cell loses touch with its neighbor(s)or with the ECM. This releases the physical constraints on the nucleus which then cycles through earlier embryonic stages hoping to establish contact once again (it partially succeeds when it establishes a metastasis).
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