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.
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.
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.
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.
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 well-being 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.