This year’s Nobel Prize for Physiology or Medicine was awarded to three researchers who studied the internal biological clock that regulates day and night cycles in sync with the Earth’s rotation.
Jeffrey C. Hall, Michael Rosbash and Michael W. Young were jointly awarded the prize for their discovery of molecular mechanisms controlling this circadian rhythm.
Using fruit flies as a model, they isolated a gene that controls the natural day-night cycle of most living beings, including humans, animals and plants. This gene codes for a protein that builds up in cells when it is nighttime. During daytime, the protein is degraded. They also worked out other molecular components that fine-tune this complex cycle.
This fundamental biological clock adapts an organism to environmental changes that vary depending on the time of day.
For instance, this cycle influences the bloom of flax flowers in the morning and their dropping off later in the day.
Jet lag, when people move rapidly between time zones, occurs when the circadian rhythm is disrupted. Horses that travel across time zones for competitions also experience disruptions to this internal clock, which may affect athletic performance. Beyond feeling groggy after a long flight, this biological clock influences many other systems in the body, which may have a profound effect on health and disease in animals and people.
Research in laboratory mice has shown that the internal clock influences metabolism in nearly every cell in the body. The detoxifying functions of the liver and kidney fluctuate with the time of day, as does body temperature.
The clock also influences food and energy metabolism, including fluctuations in blood sugar regulation, protein and fatty acid metabolism. Mice that were genetically modified to have abnormalities in the genes that control this biological clock are prone to overeating, obesity and even diabetes.
The tightly connected and important link between the biological clock and metabolism means that the body adapts to feeding times and ramps up the necessary functions to process the impending meal. The enhanced understanding of the circadian rhythm suggests that consistent feeding times are important for health and optimal physiology and not just to satiate the impatient animal demanding food.
The stress hormone cortisol fluctuates depending on the time of day, which in turn has significant effects on the immune system. The interaction between the body’s clock and the immune system means that treatment of certain diseases and vaccine administration may be enhanced based on the time of day.
Lactation in cattle is influenced by the photoperiod (the length of day and nights), even if these seasonal changes occur during the dry period.
Diseases such as founder and other disorders related to obesity in horses may be related to the internal clocks of fat cells.
This clock even influences blood clotting. Horses that are worked on a consistent schedule experience enhanced blood-clotting abilities during those exercise periods. This is probably an adaptation to micro-bleeds that occur with exercise. Racing horses in the afternoon and evening but training them in mornings may be a factor that contributes to lung bleeding seen in racing horses.
We artificially change the photoperiod of domestic animals for production and management purposes, but the effects of this on disease remain to be investigated.
For instance, breeders may keep horses under artificially long days to stimulate their reproductive cycling earlier than normal.
Under natural daylight, chickens start to lay eggs when day length increased in the spring. Based on this tendency, chicken producers increase the light period for young laying hens to stimulate egg production.