Mouse hepatocytes are smallest at the end of the day (left) and largest at the end of the night (right).UELI SCHIBLER, UNIVERSITY OF GENEVASeveral years ago and somewhat by accident, researchers led by Ueli Schibler, now professor emeritus at the University of Geneva in Switzerland, noticed that mouse liver cells are larger toward the end of the night and smaller at the end of the day. In a study published today (May 4) in Cell, the group has not only confirmed that hepatocyte size oscillates daily, but that the entire liver is larger at night when mice are most active. The observed changes in cell and organ size are related to feeding-fasting cycles and are accompanied by increased protein levels and ribosome assembly.
“This is fundamental work,” Carrie Partch of the University of California, Santa Cruz, who was not involved in the study told The Scientist. “The ribosome is this universal machine, and the thought that you have a clock controlling its assembly and tuning when it’s most active is really exciting.”
Schibler and colleagues determined that hepatocyte size swelled throughout night then shrunk during the day. But they only observed this oscillation when they fed the mice at night. When mice were fed during the day, when they are less active, that clear rhythm disappeared, even though the animals ate similar amounts of food.
These cellular cycles appeared to affect the liver as a whole. At the end of the animals’ active period, the livers of night-fed ...
