Liver Regeneration Clocks On

摘要

It has been known for decades that unicellular organisms such as cyanobacte-ria, protozoans, and algae harbor at least two different cellular devices for measuring time: the cell division clock and the circa-dian clock. For many of these simple organisms, cell division clocks are strongly influenced by the environmental milieu, in particular by temperature and the availability of food. In contrast, circadian oscillators are only marginally affected by changes in temperature and food availability, that is, they show temperature and metabolic compensation. Despite these apparently fundamental differences between the cell cycle clock and the circadian pacemaker, the latter strongly affects the former in the single-celled algae Euglena and Clamydomonas, and in cyanobacteria. In these organisms, the circadian timekeeper determines permissive daily time windows during which cells can traverse certain stages of the cell cycle or simply can di-vide more frequently.