Minutes after eating, as nutrients rush into the bloodstream the body makes massive shifts in how it breaks down and stores fats and sugars. Within half an hour, the liver has made a complete switch from burning fat for energy to storing as much glucose, or sugar, as possible. It's too short a time span for the liver's cells to activate genes and produce the RNA blueprints needed to assemble new proteins to guide metabolism.
Liver cells store up pre-RNA molecules involved in glucose and fat metabolism. ''The switch from fasting to feeding is a very quick switch and human physiology has to adapt to it in the right time frame," says Satchidananda Panda, a professor in the Salk Institute's Regulatory Biology Laboratory. It was known that a RNA-binding protein called NONO was implicated in regulating daily ("circadian") rhythms in the body.
Researchers analyzed levels of NONO in response to feeding and fasting in mice. After the animals ate, speckled clumps of NONO suddenly appeared in their liver cells, newly attached to RNA molecules. Within half an hour, the levels of corresponding proteins-those encoded by the NONO-bound RNA increased.
After mice eat, it looks as if NONO brings all these RNAs together and processes them so they can be used to make proteins. When mice lacked NONO, it took more than three hours for levels of the same proteins involved in processing glucose to increase. During that time lag, blood glucose levels shot up to unhealthy levels.
Since blood glucose levels are also heightened in diabetes, the researchers think that the mice without NONO may act as a model to study some forms of the disease. NONO has been found at high levels in the brain and muscle cells.
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