Clock genes of mammalian cells: Practical implications in tissue culture

Abstract

The clock genes family is expressed by all the somatic cells driving central and peripheral circadian rhythms through transcription/translation feedback loops. The circadian clock provides a local time for a cell and a way to integrate the normal environmental changes to smoothly adapt the cellular machinery to new conditions. The central circadian rhythm is retained in primary cultures by neurons of the suprachiasmatic nuclei. The peripheral circadian rhythms of the other somatic cells are progressively dampened down up to loss unless neuronal signals of the central clock are provided for re-entrainment. Under typical culture conditions (obscurity, 37 +/- 1 degrees C, 5-7% CO(2)), freshly explanted peripheral cells harbor chaotic expression of clock genes for 12-14 h and loose, coordinated oscillating patterns of clock components. Cells of normal or cancerous phenotypes established in culture harbor low levels of clock genes idling up to the re-occurrence of new synchronizer signals. Synchronizers are physicochemical cues (like thermic oscillations, short-term exposure to high concentrations of serum or single medium exchange) able to re-induce molecular oscillations of clock genes. The environmental synchronizers are integrated by response elements located in the promoter region of period genes that drive the central oscillator complex (CLOCK:BMAL1 and NPAS2:BMAL1 heterodimers). Only a few cell lines from different species and lineages have been tested for the existence or the functioning of a circadian clockwork. The best characterized cell lines are the immortalized SCN2.2 neurons of rat suprachiasmatic nuclei for the central clock and the Rat-1 fibroblasts or the NIH/3T3 cells for peripheral clocks. Isolation methods of fragile cell phenotypes may benefit from research on the biological clocks to design improved tissue culture media and new bioassays to diagnose pernicious consequences for health of circadian rhythm alterations.

Diurnal profiling of neuroendocrine genes in murine heart, and shift in proopiomelanocortin gene expression with pressure-overload cardiac hypertrophy

“…We then examined temporal gene expression of POMC in the Movas-1 cells. The cells were synchronized by serum shock, consistent with methods for inducing circadian gene cycling in vitro (Kaeffer & Pardini 2005). Movas-1 cells with serum shock showed a distinct pattern in POMC expression, and this differed significantly from untreated controls at the 12-and 36-h time points (P!0 .…”

Melatonin, the circadian multioscillator system and health: the need for detailed analyses of peripheral melatonin signaling

“…This has been interpreted as a reason for the disappearance of numerous rhythms in vegetative organs of SCN‐ablated animals. However, cells in culture may re‐start to oscillate when exposed to serum pulses or exchanges of medium [20]. Moreover, an apparent loss of rhythmicity can be the consequence of desynchronization among cells.…”

The circadian gene NPAS2 is a novel prognostic biomarker for breast cancer

“…Circadian oscillations are maintained by transcriptional/posttranslational feedback loops among the core circadian genes [3]. Up to now, nine mammalian core circadian genes have been identified, which are expressed in the SCN as well as peripheral tissues [4]. NPAS2 is the largest circadian gene (176.68 kb) and is located on chromosome 2 at 2q11.2 [5].…”