Immortal Time: Circadian Clock Properties of Rat

Cell lines derived from the rat suprachiasmatic nucleus (SCN) were screened for circadian clock properties distinctive of the SCN in situ. Immortalized SCN cells generated robust rhythms in uptake of the metabolic marker 2-deoxyglucose and in their content of neurotrophins. The phase relationship between these rhythms in vitro was identical to that exhibited by the SCN in vivo. Trans-plantation of SCN cell lines, but not mesencephalic or Þbroblast lines, restored the circadian activity rhythm in arrhythmic, SCN-lesioned rats. Thus, distinctive oscillator, pacemaker, and clock properties of the SCN are not only retained but also maintained in an appropriate circadian phase relationship by immortalized SCN progenitors. Recent progress has unveiled the identities and distribution of putative molecular com-ponents of the mammalian circadian clock. Orthologs of the Drosophila period gene, mPer1, mPer2, and mPer3, and the mous