Post by Theropod on Dec 31, 2013 15:42:53 GMT
Enzyme that produces melatonin originated 500 million years ago, NIH study shows
Origins of “timezyme” have implications for understanding sleep, retina disorders
An international team of scientists led by National Institutes of Health researchers has traced the likely origin of the enzyme needed to manufacture the hormone melatonin to roughly 500 million years ago.
Their work indicates that this crucial enzyme, which plays an essential role in regulating the body’s internal clock, likely began its role in timekeeping when vertebrates (animals with spinal columns) diverged from their nonvertebrate ancestors.
Origins of Timezyme: Evolutionary tree showing development of AANAT enzyme. At base of tree is a vertebrate ancestor, labeled as having non-vertebrate AANAT. This form detoxifies potentially hazardous substances. Two lines trace the evolution of non-vertebrate AANAT, which follows one branch, and vertebrate AANAT, which splits off into another set of branches. Along the trunk, labels identify where the AANAT gene duplicates, about 500 million years ago, and then where vertebrate evolution takes place. Silhouettes of elephant shark and ratfish, animals that are representative of early vertebrates, indicate that researchers found both non-vertebrate and vertebrate forms of AANAT in these animals. Further up the trunk, catshark and sea lamprey silhouettes are labeled as having only the vertebrate form of the enzyme. This vertebrate form, also called the timezyme, is found in the brain’s pineal gland and is essential for producing melatonin, which regulates the body’s internal clock.
After analyzing DNA from sea creatures thought to resemble early vertebrates, researchers have pieced together a theory of pertaining to the origin of melatonin, which regulates the body’s 24 hour daily rythms. The AANAT enzyme, or timezyme, is essential for producing melatonin. One form of AANAT is found only in non-vertebrates, and appears to detoxify potentially hazardous compounds. The researchers contend that a second copy of the gene for producing AANAT appeared about 500 million years ago, when the original gene was duplicated. As vertebrate animals evolved, the second copy of the AANAT gene evolved, eventually specializing in producing melatonin. The theory also holds that the original copy of the AANAT gene later disappeared, and its function was taken over by other genes. In support of their theory, the researchers discovered that two animals thought to be like early vertebrates, the elephant shark and the ratfish, produce both the non-vertebrate and vertebrate forms of AANAT. Two other animals thought to have originated later in vertebrate evolution, the catshark and the sea lamprey, had only the vertebrate AANAT gene.
An understanding of the enzyme’s function before and after the divergence may contribute to an understanding of such melatonin-related conditions as seasonal affective disorder, jet lag, and to the understanding of disorders involving vision.
The findings provide strong support for the theory that the time-keeping enzyme originated to remove toxic compounds from the eye and then gradually morphed into the master switch for controlling the body’s 24-hour cyclic changes in function.
Read more at: www.nih.gov/news/health/dec2013/nichd-23a.htm