26 May 1998

Pigment-Powered Body Clock

In what has been hailed as a discovery of "ground breaking" importance, scientists have identified a new light-sensitive pigment in the eye, the skin and part of the brain that controls the body's internal clock. The implications of the discovery are said to be enormous, contributing to our understanding of matters as diverse as jet lag, breast cancer rates and industrial accidents like Chernobyl.

"We are extremely excited about this fundamental discovery because it appears to be so central to mental and physiological functioning," says Aziz Sancar, professor of biochemistry and biophysics at the University of North Carolina at Chapel Hill where the research was conducted.

Announcing their findings in the May 26 issue of the Proceedings of the National Academy of Sciences, Sancar and his colleague Yasuhide Miyamoto describe how the pigment, called cryptochrome or CRY, appears to control the twenty-four-hour biological timer - or circadian rhythm - that regulates a host of bodily functions. Synchronized to light and dark, the clock affects everything from blood pressure rates to intellectual performance, sleeping and wakefulness.

"Understanding how circadian rhythm works has many practical applications," says Sancar. "First, individuals with a disease called seasonal affective disorder, or SAD, suffer serious depression during the winter months with short daylight. It may be that SAD patients have a defective gene that doesn't produce the pigment properly."

Cryptochrome may also explain why industrial disasters such as Three Mile Island or Chernobyl tend to occur at night, as illustrated by independent research carried out elsewhere. "That's because people's circadian clocks have told them it is time to slow down, and mistakes are more likely," says Sancar. The question of why breast cancer rates have risen this century might also be answered - with long exposure to electric lights disrupting normal hormone patterns.

"Only rarely do scientists make observations that are of such fundamental importance," comments David Lee, chair of biochemistry and biophysics at UNC-CH. "And since human health and well-being are intimately tied to normal cycling of the biological or circadian clock, [Dr Sancar's] discovery has important, long-term implications."