| A thesis presented on the temporal regulatory mechanism of food-entrained behavior and gene expression. Behavioral studies of food anticipatory activity in Clk/Clk mutant and NPAS2-deficient mice were undertaken to examine possible roles for CLOCK and NPAS2 proteins in the ability of mice to adapt to daytime restricted feeding. CLOCK is a core component of the light-entrained circadian oscillator in the suprachiasmatic nucleus and is expressed in rhythmic tissues throughout the brain and periphery. NPAS2 is a CLOCK homolog of unknown function highly expressed in the forebrain. Temporal gene expression profiles for circadian clock genes Per2, Bmal1, Npas2, and the catabolic and synthesizing enzymes of heme, heme oxygenase 1 and delta-aminolevulinate synthase 1, respectively, were determined in liver and forebrain tissue. The response of these genes in their phase change and amplitude, after manipulations of food availability, light cycle, and heme levels was examined. The results indicate that the food-entrainable oscillator(s) does not require CLOCK protein, but is affected by defects in NPAS2. A circadian clock in the liver, based on NPAS2:BMAL1 dimerization, is phase shifted by daily food restriction and also by the removal of food for one night. Restricted availability of food, but not food deprivation alone, affects certain circadian genes in the forebrain independent of the circadian transcription-translation feedback loop. The CLOCK protein homolog NPAS2 demonstrates a food- and deprivation-responsive circadian rhythm in the liver that may constitute an independent peripheral clock in this tissue. By understanding how restricted feeding can reset circadian rhythms in the food-entrainable clock, we gain knowledge on how food is a temporal organizing cue under normal conditions. |
