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Insight into how the body tells time

ton University team capitalized on the genome database now available. Using a relatively new technology called DNA microarrays comprehensive lists of all the active genes in a tissue sample they measured the expression levels of nearly 14,000 genes at various time-points in the heads of normal flies and in flies missing one of the clock genes, called period.

All flies were exposed to light for 12 hours, followed by dark for 12 hours. The cycle continued for a total of 96 hours. Genetic analyses were performed on half of the flies at six different time-points on the fifth day.

The remaining flies were transferred into complete darkness for 48 hours. On the third day of darkness, the team again analyzed gene expression at each of six time-points. By exposing flies to constant darkness, the team hoped to detect genetic changes that are regulated by the internal circadian timekeeping system, rather than by external cues.

Overall, the researchers obtained over 70 readings for each of the nearly 14,000 genes, generating about a million individual measurements.

Using sophisticated computer-based statistical analyses, the team determined that between 72 and 200 of the flies' 14,000 genes showed significant rhythms of gene expression in normal flies living in a daily light-dark cycle. Of these 72 genes, 22 continued to fluctuate when flies were collected after three days of complete darkness. This implies that these 22 genes are driven by the internal, circadian clock, not by external cues such as light.

Mutant flies lacking the period gene also were placed into the same two experimental conditions light and dark fluctuations compared with complete darkness. The flies exposed to alternating light and dark still showed 18 genes with persistent, rhythmic oscillations, demonstrating that light and dark can directly drive rhythmic gene expression.

The remaining 32 of the 72 oscillating genes only fluctuated rhythmically in anim
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Contact: Gila Z. Reckess
reckessg@msnotes.wustl.edu
314-286-0109
Washington University School of Medicine
24-Jun-2002


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