View Full Version : Science: Humans may sense light through skin

17th November 2008, 04:14 PM
Humans may sense light through skin
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14 July 2008

A team of researchers from Europe and the US has shown that a type of
protein molecule found in many different human tissues can respond to
light. The finding raises the intriguing possibility that humans might
be able to detect light through skin as well as the eye.

Margaret Ahmad from the University of Paris VI, France, and her
colleagues focused on a class of photoreceptor proteins called
cryptochromes, which are activated by light in plants and trigger a
number of physiological responses, such as maturation of seeds and
unfurling of leaves. Cryptochromes are also found in insects and
mammals, including humans. But until now no-one has known whether
human cryptochromes react to light.

Ahmad and her team used a range of spectroscopic techniques to show
that the pigment flavin is the photoreactive component of the human
cryptochrome, as it is in plants, and that in its resting state it is
oxidised, becoming reduced in response to blue light.

The researchers then examined the response of human cryptochrome to
light in a genetically engineered strain of the fruit fly Drosophila.
They showed that in a living organism the protein also changed when it
was exposed to light. 'These results provide the first evidence of how
animal-type cryptochromes are activated by light in living cells,' the
researchers say.

Charalambos Kyriacou, an expert in biological clocks at the University
of Leicester in the UK, remains cautious about ascribing a
light-sensing role to cryptochromes in non-visual cells in humans. 'In
humans we know that blind people do not have a body clock at all, and
that all the evidence so far says that we can only sense light through
our eyes,' Kyriacou says, pointing out that in the fruit fly
cryptochrome molecules in nerve cells act as light receptors while
identical molecules in other tissues do not. It is possible that the
light-sensing properties of the molecule are repressed depending on
the cellular environment of the cryptochrome, Kyriacou suggests.

Simon Hadlington