Video transcript: How the eye regulates your body clock: Ri Christmas Advent Calendar 2013 Chromosome 10
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Video shows a woman sleeping and close ups of a number of eyes
Professor Russell Foster, University of Oxford
Chromosome 10 is extraordinary! We all know what it is like if we are forced out of bed way before 5 o'clock in the morning, it takes us a long time to wake up. We all have a day within our biological clock also called a circadian clock and what this does, and it really can't be over emphasised, is regulate almost every aspects of our physiology and behaviour, fine turning physiology and behaviour to the varying demands of activity and rest, cranking up hormones and metabolism in anticipation of activity, and turning it down again in anticipation of sleep.
Video shows Professor Foster with a model diagram of an eye
So the sleep-wake cycle, changes in blood pressure, changes in temperature still show a near 24 hour oscillation but it wouldn't be exactly 24 hours and so what needs to happen every day is that this slightly drifting clock needs to be adjusted to environmental time and the most important signal that the clock needs is exposure to the light-dark cycle and that light-dark is detected in mammals, such as ourselves, by light-detecting cells within the eye.
It is critically important that the body clock is adjusted everyday by the light-dark cycle and if you didn't get that daily adjustment then internal time would be abnormally synchronised with the external world and perhaps the best example of that is jet lag. So we knew that these photo receptors were in the eye because if you prevented light getting to the eye then the body clock no longer responded to light, so something in the eye. But the big problem was is that it was very difficult to understand how the classical visual cells of the eye could be detecting overall brightness of the environment.
Video shows various motion images of someone shuffling a pack of cards
For the vision to work the visual cells grab light, they send that information off into the brain and then essentially they stop working so you have series of sharp images and it was very difficult to understand how that image-detecting system could also get an appreciation of the overall amount of brightness and hence time of day. So there was a big puzzle.
Video shows mice
We started using mice in which the rods and cones had largely degenerated as a result of inherited retinal diseases. So these mice had lost most of their rods and cones so were visually blind and we wanted to see whether they could still regulate their body clocks and what was absolutely extraordinary is that these visually blind mice were able to regulate their body clock to the light-dark cycle perfectly normally. The mouse would get up, run in its running wheel and go to bed at the same time day after day after day. And so we thought my goodness there is something really interesting going on here. There had to be another class of light-sensitive cell within the eye and the big question of course is well if it is not the rods and cones then which of the cells of the inner retina could it possibly be? Eventually, the light-sensitive molecule was found and it was called melanopsin, or OPN4, and that gene is located on chromosome 10.
Video shows people wearing glasses
I think knowledge about this new system is really very important. If you think about it, we know that there is about 40 million people worldwide who have no sense of visual sensitivity at all. Now understanding that there is another light sensor within the eye could hugely improve the quality of life and the sense of wellbeing of those individuals and at the moment very little is discussed about those cells. So the fact that melanopsin is turning up in chromosome 10 makes chromosome 10 my favourite chromosome.
- Production: Joy Ng
- Music: Chris Zabriskie, Asthmatic Astronaut, Origamibiro, Augustus Bro and Gallery Six
- Special thanks: Russell Foster
Supported by BBSRC. © The Royal Insitution 2013.