Transcriptome Dynamics During the Mammalian Cell Cycle
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TRANSCRIPTOME DYNAMICS DURING THE MAMMALIAN CELL CYCLE. Daniel I. Dominguez A dissertation submitted to the faculty of the University of North Carolina at Chapel Hill in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Pharmacology Chapel Hill 2014 Approved by: Zefeng Wang Gary L. Johnson William Marzluff Lee M. Graves Henrik Dohlman © 2014 Daniel I. Dominguez ALL RIGHTS RESERVED ii ABSTRACT DANIEL I. DOMINGUEZ: Transcriptome Dynamics during the Mammalian Cell Cycle. (Under the Direction of Zefeng Wang, Ph.D.) In recent years, technologies capable of simultaneously deciphering the nucleotide sequence and expression level of most RNAs in the cell have challenged the simplistic view of one gene-one protein. It is now well-appreciated that the cell has a tremendous level of flexibility during RNA processing (i.e. alternative splicing) to produce multiple coding mRNAs from single gene unit. Another surprising find is that most of the genome is transcribed, which leads to the production of a large proportion of RNAs without coding potential (i.e. lncRNAs). Global transcriptome rearrangements have been shown to occur during and regulate key biological processes like development and differentiation. This work focuses on bettering our current understanding of the mammalian cell cycle in the context of transcriptome-wide dynamics. Progression through the mitotic cell cycle has been shown to require periodic gene function. Conventionally, these biological oscillations are thought to be primarily mediated by transcription and protein degradation. Here we report sequencing of the human transcriptome through two continuous cell cycles, revealing periodic dynamics of over 1,000 coding and non-coding RNAs. Additionally, we uncovered widespread periodic splicing events, many of which affect genes that regulate cell cycle. Mechanistically, we show that Cdc2-like kinase 1 undergoes periodic fluctuations through an auto-inhibitory circuit to control a network of iii periodic splicing events that are required for cell cycle. Our findings elucidate a novel mechanism for periodic gene regulation independent of transcription, suggesting that proteome expansion via splicing adds a new regulatory layer for control of gene function during cell division. iv ACKNOWLEDGEMENTS I would like to thank my advisor, Zefeng Wang, for his continued support over the last five years. When I came to UNC, Zefeng was new at running a lab and I was new at being a graduate student. I think we have done awesome together. Zefeng is a brilliant scientist with a ton of foresight, so I really appreciate that he let me see some of my ideas through, even when they seemed likely to fail. Altogether, I couldn’t be happier with the relationship that we have developed. I am also thankful for the members of the Wang lab, past and present: Yang Wang, Rajarshi Choudhury, Shannon Tsai, Meng Ma, Shuyun Dong, Wenjing Zhang and Russell Maxwell. Yang and Raj were especially helpful in the early days, when the lab was still acquiring momentum. Russell worked alongside with me for a few years to ensure all work gets done. I am also grateful for my thesis committee members: Gary Johnson, Lee Graves, Bill Marzluff and Henrik Dohlman. I thank you for being extremely helpful in both science and career advice. UNC has been a great place to work. The Pharmacology department is full of talented folks that are always willing to chat about science and lend a helping hand. I am highly appreciative of the opportunity to do science here. v TABLE OF CONTENTS LIST OF TABLES ............................................................................................................ ix LIST OF FIGURES .......................................................................................................... x LIST OF ABBREVIATIONS ............................................................................................ xii CHAPTERS I. Introduction ....................................................................................................... 1 The mitotic cell cycle ................................................................................... 1 Regulation of cell cycle progression ................................................ 2 RNA dynamics during the cell cycle ........................................................... 4 The cycle-dependent gene expression program ............................. 4 The G1/S wave ............................................................................... 6 The G2/M wave ............................................................................... 9 The M/G1 wave ............................................................................... 9 Quality control checkpoints ........................................................................ 9 The DNA-damage checkpoint ....................................................... 10 The spindle assembly checkpoint ................................................. 11 RNA processing ...................................................................................... 12 Transcription, RNA splicing and alternative splicing ..................... 12 SR proteins ................................................................................... 13 CLK kinases .................................................................................. 15 Cellular regulation of CLK kinases ................................................ 18 CLK inhibitors ................................................................................ 19 vi CLK homologs............................................................................... 19 Global gene expression by CLKs ................................................. 20 Connections between cell cycle and splicing ........................................... 20 Thesis objectives ..................................................................................... 23 II. Materials and methods .................................................................................. 24 Chapter III ................................................................................................ 24 Chapter IV ................................................................................................ 30 Chapter V ................................................................................................. 33 III. Transcriptome dynamics during the mitotic cell cycle ................................... 35 Introduction .............................................................................................. 35 Results ..................................................................................................... 37 Sequencing the cell cycle-dependent transcriptome ..................... 37 Identification, function and regulation of periodic genes ................ 38 Consistency across datasets ........................................................ 40 Identification of periodic alternative splicing .................................. 42 Putative cis-elements and trans-factors that regulate periodic AS ............................................................... 44 Discussion ............................................................................................... 45 IV. CLK1 kinase controls cell cycle processes via an alternative splicing network .......................................................... 57 Introduction .............................................................................................. 58 Results ..................................................................................................... 58 CLK1 is cell cycle regulated .......................................................... 58 CLK1 protein turnover ................................................................... 59 vii CLK1 a kinase is engaged in negative ......................................... 60 CLK1-mediated transcriptome regulation ..................................... 62 CLK1 control CENPE alternative splicing ...................................... 63 CLK1 and SFRS1 regulate CHEK2 splice .................................... 64 CHEK2 variants have different biochemical properties ................ 65 CLK1 is required for normal cell cycle progression and proliferation ......................................... 67 Discussion ............................................................................................... 69 IV. Mitotic trait: A computational method for inferring cell-cycle stage ............... 89 Introduction .............................................................................................. 89 Results ..................................................................................................... 91 Mitotic trait of cells based on transcriptome profile ....................... 91 Mitotic trait of single cells from the human embryo ....................... 92 Mitotic trait of human breast cancers and correlation with molecular subtypes ....................................... 93 Pan-cancer mitotic trait analysis.................................................... 94 Discussion ............................................................................................... 94 VI. Concluding remarks .............................................................................................. 102 Summary ............................................................................................... 102 Outstanding questions ..........................................................................