A SERUM SHOCK INDUCES CIRCADIAN GENE-EXPRESSION IN MAMMALIAN TISSUE-CULTURE CELLS

The treatment of cultured rat-1 fibroblasts or H35 hepatoma cells with high concentrations of serum induces the circadian expression of vari ous genes whose transcription also oscillates in living animals. Oscil lating genes include rper1 and rper2 (rat homologs of the Drosophila c lock gene period), and the genes encoding the transcription factors Re v-Erb alpha, DBP, and TEF. In rat-1 fibroblasts, up to three consecuti ve daily oscillations with an average period length of 22.5 hr could b e recorded. The temporal sequence of the various mRNA accumulation cyc les is the same in cultured cells and in vivo. The serum shock of rat- 1 fibroblasts also results in a transient stimulation of c-fos and rpe r expression and thus mimics light-induced immediate-early gene expres sion in the suprachiasmatic nucleus.