Fri, 27 Apr 2007 11:45 CDT
A genetic mutation called the "after-hours gene" may explain why some people are night owls, it is revealed in Science journal today.
It could also hold clues for pharmacologists working to develop drugs to help people adjust to shift work or jet lag. There are further implications for the study of causes of some psychiatric disorders.
The altered gene, named "after hours" or Afh, is a variant of a gene called Fbxl3, which had not been linked to the body clock that keeps our metabolism, digestion and sleep patterns in tune with the rising and setting of the sun.
The discovery involved scientists from the Medical Research Council Mammalian Genetics Unit, Oxfordshire, the MRC Laboratory for Molecular Biology, Cambridge, and colleagues based at New York University.
Pharmaceutical companies are already beginning to study this class of proteins as potential drug targets.
By monitoring when and how often the mice chose to run on an exercise wheel the team spotted a change in some of the animals' normal rhythms.
Instead of following the typical 24 hour pattern, some of the mice had body clocks that stretched to up to a 27 hour day.
Closer study of the DNA from the mice then revealed that those on a 27-hour-cycle had the after hours version of the Fbxl3 gene, one of a large family that controls the breakdown of specific proteins within body cells.
Dr Patrick Nolan, of the MRC Mammalian Genetics Unit, who led the study said: ''The internal body clocks of mice with the after hours gene run on a longer cycle than mice that have a normal copy of the gene, who like most of us live on a 24 hour schedule.''
The "cogs" of the body clock consist of interlocked cycles of proteins that wax and wane in cells. One of the key components of this loop is a protein called Cry.
"We found that mice that carried the after hours gene also had a delayed Cry protein breakdown rate, leading to a slowdown in the molecular feedback loops and a lengthening of the body clock cycle.''
In other research, scientists have identified a part of the brain that affects how we deal with seasonal change.
The research will help our understanding of the causes and consequences of seasonal affective disorder and could also shed light on why we crave more food in winter.
Dr Gerald Lincoln, of Edinburgh University's Centre for Reproductive Biology, said: "Surprisingly, the circannual body clock works on a 10-month cycle.
"We reset our body calendar every summer, when increased light inhibits the production of melatonin. This could explain why sunshine makes us feel happier."