Chromosome 10 is extraordinary.
We all know what it's like if we're 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, a biological clock, also called
a circadian clock.
And what this does--
and it really can't be overemphasised--
is regulate almost every aspect of our physiology and
behaviour, fine tuning 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's critically important that the body clock is adjusted
every day by the light-dark cycle.
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 photoreceptors were in the
eye, because if you prevented light getting to the eye, then
the body clock no longer responded to light.
So there's something in the eye.
The big problem was that it was very difficult to
understand how the classical visual cells of the eye could
be detecting overall brightness within the
environment.
For 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 a 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 inheritive retinal diseases.
So these mice had lost most of their rods and cones.
They 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 then 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's 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's about 40 million
people worldwide who have no sense of visual
sensitivity at all.
Now understanding that there's 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.