Genome-Wide Studies on the Molecular Functions of Pax7 in Adult Muscle Satellite Cells
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Genome-Wide Studies on the Molecular Functions of Pax7 in Adult Muscle Satellite Cells Vincent Punch Thesis submitted to the Faculty of Graduate and Postdoctoral Studies in partial fulfillment of the requirements for a Ph.D. degree in Cellular and Molecular Medicine Department of Cellular and Molecular Medicine Faculty of Medicine University of Ottawa © Vincent Punch, Ottawa, Canada, 2011 ii Abstract Pax3 and Pax7 belong to a family of conserved transcription factors that play important and diverse roles in development. In the embryo, they carry out similar roles in neural and somite development, but Pax7 fails to compensate for critical functions of Pax3 in the development of limb musculature. Conversely, in the adult, Pax7 is necessary for the maintenance and survival of muscle satellite cells, whereas Pax3 cannot effectively fulfill these roles in the absence of Pax7. To identify the unique roles of Pax7 in adult muscle cells, we have analyzed global binding of Pax3 and Pax7 by ChIP-Seq. Here, we show that despite highly homologous DNA-binding domains, the majority of binding sites are uniquely recognized by Pax7 and are enriched for homeobox motifs. Genes proximal to conserved, unique Pax7 binding sites cluster into specific functional groups which may reflect the unique biological roles of Pax7. Combining Pax7 binding sites with gene expression data, we describe the regulatory networks directed by Pax7 and show that Pax7 binding is associated with positive gene regulation. Moreover, we show Myf5 is a direct target of Pax7 and identify a novel binding site in the satellite cell control region upstream of Myf5. iii Acknowledgements I would like to thank my fellow lab mates for providing an enjoyable atmosphere and constructive and creative environment. You have each contributed to this project in your own way, by stimulating thought provoking discussions, providing technical assistance, or merely social support. I especially thank Dr. Michael Rudnicki for allowing me the opportunity to undertake this research project, for providing scientific guidance and a superb environment in which to carry out this work. I would like to thank Theodore Perkins, Gareth Palidwor, Chris Porter, and Dr. Hang Yin for useful discussions and brainstorming sessions on how to best analyze our vast amount of data. I thank my advisory committee, Dr. Bernard Jasmin, Dr. David Picketts, and Dr. Luc Sabourin, for their guidance along the way. Finally, I thank my parents for their love and support over the years. You encouraged me to keep going when I wanted to give up and helped me every step of the way. iv Contributions of Collaborators and Co-Authors All technical work and preparations of the thesis and manuscripts were carried out by the thesis author except as otherwise specified. Solexa sequencing of ChIP products was carried out in full by the technical staff of Dr. Frank Grosveld at Erasmus University and Medical Center in Rotterdam, Netherlands. Gareth Palidwor and Chris Porter carried out bioinformatics analyses on ChIP-Seq data and provided the corresponding figures used throughout Chapter 2. Dr. Yoichi Kawabe provided RNA samples for the microarray analysis and all baculovirus generated protein used in these studies, in addition to contributing western blot data for Chapter 3. Dr. Vahab Soleimani provided technical assistance with sample preparation for ChIP-Seq experiments. In vivo analyses of the B195APZ BACs were carried out by Dr. Jaime Carvajal of Dr. Peter Rigby’s group at the Division of Gene Function and Regulation at the Institute of Cancer Research in London, UK. The author carried out experiments and provided data for Figures 4b, 4f, 4g, and 4h in Appendix A. v Contents Abstract .................................................................................................................................... ii Acknowledgements ................................................................................................................. iii Contributions of Collaborators and Co-Authors ...................................................................... iv Contents ..................................................................................................................................... v List of Tables .......................................................................................................................... vii List of Figures ....................................................................................................................... viii List of Abbreviations ................................................................................................................ ix Chapter 1 – General Introduction ......................................................................................... 1 1.1. An Overview of Skeletal Muscle ......................................................................... 2 1.2. Stem Cells Regulate the Growth and Regeneration of Muscle ............................ 3 1.3. Molecular Mechanisms of Myogenic Determination .......................................... 4 1.4. Mechanisms of Embryonic Myogenesis .............................................................. 5 1.5. Molecular Networks Regulating Embryonic Myogenesis ................................... 6 1.6. Satellite Cells and Adult Muscle Regeneration ................................................. 12 1.7. Self-Renewal and Commitment of Satellite Cells ............................................. 13 1.8. Extrinsic Signals Regulating Satellite Cell Activation ...................................... 16 1.9. Roles of Pax3 and Pax7 ..................................................................................... 20 1.10. Alternative Splicing of Pax3 and Pax7 .............................................................. 22 1.11. Human Phenotypes of Pax3/7 Mutations ........................................................... 22 1.12. Systems Biology Approaches to Understanding Myogenic Regulatory Networks ............................................................................................................ 23 1.13. Peripheral Networks ........................................................................................... 24 1.14. Rationale and Hypothesis .................................................................................. 25 Chapter 2 – Transcriptional Dominance of Pax7 in Adult Myogenesis is Due to High- Affinity Recognition of Homeodomain Motifs Relative to Pax3 ....................................... 27 Summary ............................................................................................................................. 29 Introduction ......................................................................................................................... 30 Results ................................................................................................................................. 33 Discussion ........................................................................................................................... 56 Experimental Procedures..................................................................................................... 61 Acknowledgements ............................................................................................................. 67 References ........................................................................................................................... 68 Supplementary Information................................................................................................. 84 Chapter 3 – Myf5 is a Direct Target of Pax7 Regulation in Adult Myoblasts ................. 90 Summary ............................................................................................................................. 92 Introduction ......................................................................................................................... 93 Results ................................................................................................................................. 96 Discussion ......................................................................................................................... 109 Experimental Procedures................................................................................................... 114 Acknowledgements ........................................................................................................... 119 vi References ......................................................................................................................... 120 Supplementary Information............................................................................................... 124 Chapter 4 – General Discussion ......................................................................................... 127 4.1. Overview .......................................................................................................... 128 4.2. Future Directions ............................................................................................. 131 4.3. Significance ...................................................................................................... 135 4.4. Biomedical Implications .................................................................................. 137 4.5. Conclusion ....................................................................................................... 138 References ............................................................................................................................