| The mammalian circadian system generates an approximate 24-hour rhythm through a complex autoregulatory feedback loop. Four genes, Period 1 (Per1), Period 2 (Per2), Cryptochrome 1 (Cry1), and Cryptochrome 2 (Cry2), regulate the negative feedback within this autoregulatory feedback loop. These codependent proteins have distinct yet complimentary roles within the core circadian mechanism; however, their mutually dependent nature makes their function complex and therefore poorly understood. Here, the tetracycline transactivator system (tTA) was used to examine the role of transcriptional oscillations in Per1, Per2, Cry1 , and Cry2 and the importance of these oscillations in the persistence of circadian activity rhythms. The results presented in this dissertation demonstrate that transcriptional oscillations of Per2, in the brain and SCN, are essential for the regulation of persistent circadian activity rhythms, while levels (and not oscillations) of Cry1 and Cry2 were found to be important regulators of circadian period. A critical period was also discovered where the level of Cry1 from birth to postnatal day 45 was found to be important in setting the endogenous free running period in the adult animal. These discoveries have provided new insights into the roles of the negative feedback elements in circadian rhythmicity and have furthered our understanding of circadian rhythms in mammals. |
