The language of cells
Laser scanning confocal microscope specially equipped for taking pictures of living cells over time
Mr John Ankers, Dr Claire Harper, Dr Violaine See and Professor Michael White
University of Liverpool
Mr Edwin Jesudason
Royal Liverpool Children's Hospital and University of Liverpool
Pioneering approaches to imaging living cells are providing the first glimpses of what may be a completely new cellular language. The 'language' used by cells to switch genes on and off has always been thought to be dependent on the amount of different proteins in cells. Michael White and his team at the Centre for Cell Imaging, University of Liverpool, think differently. 'We think it is the frequency or timing of protein movement between the cytoplasm and nucleus of a cell that carries the signal rather than the amount of protein,' says Michael.
This movement of proteins from the cytoplasm to the nucleus of a cell and back controls the switching, on or off, of genes. Unfortunately, these proteins are not normally visible, but they can be made so thanks to the natural fluorescence of jellyfish, and corals. 'Nature has provided us with a huge tool box for visualising processes in cells,' says Michael. 'Genes that code for naturally fluorescent proteins can be extracted and inserted into other cells that we are interested in.' The extracted gene can be joined to any other gene to produce a protein of interest that is visible by its fluorescence inside cells.
Alternatively, the extracted gene can be used to look at promoter activity. Gene promoters are sequences of DNA that control the activity of a gene a bit like a switch. 'By controlling a luminescent gene from a firefly with one of these switches, you can see when the gene of interest is activated as the cells begin to glow. These systems work beautifully for any cell you wish to study,' explains Michael. 'All that these luminescent proteins need in order to glow' are oxygen, a chemical adenosine triphosphate (ATP) both of which are present in all cells and luciferin which we feed to the cells.' Using fluorescence and luminescence together, the movement of proteins in and out of the cell nucleus and the affect this has on gene activity can be observed through a microscope.
'One cellular signal of particular interest is the NF-kappaB network that regulates whether cells multiply or die. This pathway has a role in a huge variety of cellular processes and diseases from cancer to inflammation. A key question is how this one signal can carry so many different messages. To us it is obvious that it has to be timing,' says Michael. 'If you think of Morse code conveyed by a flashing light, all you have are short and long flashes but the patterns they create can convey a huge amount of information.' Understanding how this pathway controls so many different functions could open up many new targets for drug treatment.
This innovative idea about cell signalling is not without controversy but other work indicates that the University of Liverpool may be right. An Israeli team has recently found that a gene known as P53 with a key role in cancer has a six-hour working cycle, which suggests timing may be critical in its function.