Clock watching gets under the skin

In a breakthrough that could help us to find better ways to combat sleep disorders and jetlag, scientists have discovered that skin and other cells can be used to tell the time of the body clock.

Previously it was thought that the body uses just one main clock to keep track of time.  This had been tracked down to a cluster of nerve cells known as the suprachiasmatic nucleus, which is situated deep within the brain's hypothalamus. Cells in this region receive inputs from the eyes so that their time can be adjusted as the length of the day changes.  The clockwork mechanism itself consists of a group of (so far) 8 genes, which turn each other on and off in sequence to produce a genetic domino effect that takes about 24 hours to complete.  As the clock "ticks" the behaviour of the nerve cells changes, leading to the secretion of hormones and other triggers, which directly affect the behaviour of different tissues around the body.

Now, writing in the journal PNAS, Zurich University researcher Steven Brown and his colleagues have found that the same patterns of activity also occur in skin cells.  The team collected small skin samples containing cells known as fibroblasts from twenty-eight healthy volunteers, seventeen of whom described themselves as "night owls" and the remaining eleven as "larks".  The team used a virus to add a gene to the cells so that they would glow brightly whenever one of their clock genes turned on.  The researchers then grew the cells in a dish and found the glowing marker gene periodically switching on and off with every 24 hour period.  But most surprisingly, the time it took to do so was different depending upon whether the skin cells came from a "lark" or an "owl" human, with the larks having a significantly shorter period than their more nocturnal counterparts.

Whilst interesting in itself, this finding shows that whilst the eyes might be the window to the soul, skin cells are a window to the workings of the body clock. "This will certainly provide us with new insights into the workings of the body clock," says "clock-doc" Russell Foster who works on circadian rhythms at Oxford University. "There are large numbers of disorders that are also associated with sleep disturbance, like schizophrenia, depression, bipolar disorder and Alzheimer's. But how much clock disturbance contributes to the symptoms of these diseases we don't know. Techniques like this will show us and also enable scientists to develop better therapies."