Can Our Biological Clock be Disrupted by Environmental Toxins?

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New research suggests that the function of our circadian rhythms (the biological clock) may be affected by environmental toxins.  It comes following the recent discovery of plankton that has now adapted to road salt pollution following a disruption to their circadian rhythm.

This research shows that exposure to environmental toxins may be depressing the function of our circadian clock, the disruption of which is linked to increased rates of cancer, diabetes, heart disease, and depression,” confirms Jennifer Hurley, senior author on the research, an assistant professor of biological sciences, and a member of the Center for Biotechnology and Interdisciplinary Studies (CBIS) at Rensselaer Polytechnic Institute. “This is the first time anyone has shown this happening at the level of the core clock, which we had considered to be heavily buffered against these types of environmental effects.”

Previous research carried out at Lake George, under the Jefferson Project, demonstrated how common zooplankton called Daphnia pulex had evolved its tolerance levels of road salt in less than three months in order to survive.  “Plankton, which are key consumers of algae and a food source for many fish, may be making a monumental tradeoff to tolerate increased road salt,” said Jefferson Project director, CBIS member, and co-author of the study, Rick Relyea.  “The circadian rhythm guides these animals through a daily migration, to deep waters during the day to hide from predators and shallow waters at night to feed.  Disrupting that rhythm could affect the entire lake ecosystem.”

According to Hurley, the adaptation to salt these plankton are undergoing is likely to induce a change in their genes.  To explore that hypothesis further, researchers first had to establish the set of clock-control genes that are responsible for governing the day/night cycle in the plankton. In the Daphnia, researchers discovered the PERIOD (PER) gene which is very similar to the set of genes found in a fruit fly that relate to the core clock.

As part of the study, first author and Rensselaer doctoral student, Kayla Coldsnow tracked the changes in mRNA of Per in Daphnia as it was exposed to dark conditions and naturally low salt levels.  What she discovered was that despite the constant conditions, the levels oscillated following a 24-hour rhythm.  This proves that PER genes are in fact active in Daphnia.

Now it was up to Coldsnow to test whether or not this adaptation had an effect on the functioning of the circadian clock.  Having compared the new data with data gathered during earlier research, she discovered that PER mRNA rhythms worsened as the plankton adapted to the increased salt concentrations.  “What we see is a graded, measured response in this organism; the higher the level of salt to which the Daphnia are adapted, the more it suppresses the expression of its circadian clock,” said Hurley.  “The population adapted to naturally low salt levels exhibits a beautiful, healthy oscillation in PER mRNA expression, but the population adapted to high salt levels have completely lost their ability to oscillate this mRNA expression.”

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