Circadian clocks and cell division

Abstract

Evolution has selected a system of two intertwined cell cycles: the cell division cycle (CDC) and the daily (circadian) biological clock. The circadian clock keeps track of solar time and programs biological processes to occur at environmentally appropriate times. One of these processes is the CDC, which is often gated by the circadian clock. The intermeshing of these two cell cycles is probably responsible for the observation that disruption of the circadian system enhances susceptibility to some kinds of cancer. The core mechanism underlying the circadian clockwork has been thought to be a transcription and translation feedback loop (TTFL), but recent evidence from studies with cyanobacteria, synthetic oscillators and immortalized cell lines suggests that the core circadian pacemaking mechanism that gates cell division in mammalian cells could be a post-translational oscillator (PTO).

Translation-independent circadian control of the cell cycle in a unicellular photosynthetic eukaryote

“…Circadian rhythms are believed to maximize fitness by enabling organisms to coordinate with the changes that occur in the 24-h environmental cycle by a temporary reorganization of a variety of cellular physiological processes 1 . Although circadian regulation of the cell cycle is evident in many eukaryotes, especially in photosynthetic organisms 3 , the specific survival benefits derived from circadian regulation of cell cycle have not yet been determined.…”

“…Circadian rhythms regulate biological processes so as to make them occur at the appropriate time in a specific environment, resulting from daily fluctuations in energy availability 1,2 . One of the biological processes controlled by circadian rhythms is the temporal gating of cell division, a phenomenon that has been observed in a wide variety of eukaryotic lineages from unicellular organisms to mammals 3 . The circadian gating of cell division is especially evident in unicellular algae, in which cells divide at night [3][4][5][6] .…”

Entrainment of breast (cancer) epithelial cells detects distinct circadian oscillation patterns for clock and hormone receptor genes

“…1), which can influence a wide range of functions outside the clock. 2,14,15 It is thought that > 10% of all mammalian transcripts undergo circadian oscillations. [16][17][18] Remarkably, nuclear receptors are functionally intertwined with the circadian oscillator.…”

Rhythmic profiles of cell cycle and circadian clock genes' transcripts in mice: a possible association between two periodic systems

“…Several explanations can be proposed for the non-circadian phenotype: (i) the esophagus harbors neither a self-sustaining nor a SCN-paced circadian time device; (ii) the circadian phenotypes of other variables in the esophagus (but not the analyzed clock genes) are directly governed by the SCN and not by the tissue's clock; and (iii) genes other than Per2 (Per1 for example) function as the principal factors in the negative limb of the esophagus rhythm (Johnson, 2010). However, the relatively large amplitude of the Per2 mRNA rhythm does not favor this alternative.…”

“…The choice of Clock and Per2 was based on studies that include these genes as regulators in the gating of the cell cycle stages (G1 to S transition) (Johnson, 2010;Lahti et al, 2012). Locomotor activity was monitored in order to establish the circadian organization of the SCN's master pacemaker (Davis and Viswanathan, 1996;Earnest et al, 1999;Reebs and Maillet, 2003).…”