Regulation of pre-ribosomal RNA by the Circadian Clock

University Of California-Irvine, Irvine CA

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Abstract

Project Summary Disruptions of the body's internal circadian clock by means such as jet lag, a lack of sleep or shift work can affect biological functions and lead to disease. Becoming more familiar with the regulation of circadian rhythms will allow for a better understanding of pathologies such as obesity, diabetes, and cancer and the development of therapeutic treatments for these diseases. On a molecular scale, the circadian clock controls many cellular mechanisms that give the biological clock the ability to remain at a constant 24-hour period. The core clock machinery, CLOCK and BMAL1, regulates transcription of clock-controlled genes. Additionally, CLOCK has also been found to have a non-traditional role in post-translational modifications such as the acetylation levels of circadian proteins. However, additional roles for BMAL1 are not well identified. Hints provided by recent discoveries indicate the clock is involved RNA polymerase 1 (Pol I)-mediated transcription. Pol I transcribes ribosomal DNA (rDNA) that is further processed to mature ribosomal RNA (rRNA) through a series of post-transcriptional modifications. The rRNA precursor, (pre-rRNA), is a tandem repeat that contains 18S, 5.8S and 28S rRNAs. A study on circadian nuclear protein accumulation has shown an oscillatory expression pattern of nucleolar proteins involved in pre-rRNA processing. Based on the recent findings, the goal of this project is to elucidate the function of the circadian clock on the regulation of pre-rRNA. This study will explore the undiscovered mechanism for the circadian pre-rRNA expression. First, a novel BMAL1 subcellular localization will be identified and fully characterized. Further, the circadian regulation of pre- rRNA will be investigated by preforming analyses to locate the sites of BMAL1 recruitment to rDNA. Measurements of the Pol I transcriptional activity in a clock-dependent manner will define the role of the circadian clock on pre-rRNA transcription. Additionally, this research study will identify a novel role for BMAL1 on pre-rRNA maturation. The importance of a physical interaction between BMAL1 and the nucleolar proteins will be thoroughly established. Followed by a comprehensive analysis of the role of the circadian clock on nucleolar structural integrity. Lastly, we will test the significance of the nucleolar BMAL1 in pre-rRNA processing. We believe we will characterize the functional relevance of BMAL1 in the nucleolus. !