Critical Role of Transcription Cofactor PC4 in Mammals

Diese Dissertation wurde selbständig und ohne unerlaubte Hilfe erarbeitet. ACKNOWLEDGEMENTS I am very grateful to Prof. Dr. Michael Meisterernst for giving me the opportunity to work with him and for guiding me in the field of transcription. I am thankful for his constant support and guidance throughout my work. I am thankful to all the current and former lab members, especially, Ulrike Niehues for taking care of mice and all the technical help. I would like to thank former member Dr. Wera Roth who was initially involved in designing the conditional knockout-targeting vector for this project and also for constant guidance. I thank former member Gertraud Stelzer for making a lot of contribution to generating the constitutive knockout mouse model. Many thanks to Dr. Thomas Albert for the critical comments on this manuscript. I enjoyed all the scientific and non-scientific discussions with my friends Ming, Tasneem and Caroline and thank them for the pleasant atmosphere in the lab. Guangming Wu from his lab, who helped me to generate knockout ES cell lines and also taught me many techniques related to this work. who gave me a lot of invaluable help and advice. Finally, I would like to thank my husband and my family for their love, support and all the encouragement throughout these years. SUMMARY PC4 is a small protein with unique DNA-binding properties that affects transcription and has presumptive roles in DNA repair and genome stability. It was originally isolated from a cofactor fraction termed the ''upstream stimulatory activity'' (USA) of HeLa cell nuclear extracts. The cofactor has been shown to broadly enhance RNA polymerase II-driven gene transcription in the presence of activators (e.g., hormone receptors, viral activators, cell-specific and ubiquitous activators). Although such data imply that PC4 is a very important factor in vivo, human tumor cell lines with PC4 knockdowns are without obvious phenotypes. To further study the in vivo role of PC4, we constructed constitutive and conditional knockout mouse models as well as knockout embryonic stem cells. Mammalian PC4 is here shown to be an essential factor during early embryogenesis. PC4-/-embryos develop normally until E5.5, but then degenerated around E7.5. PC4 knockout ES cell lines were generated from PC4-/-blastocysts (E3.5), which develop normally from 2-cell stage embryos. All PC4 knockout ES cell lines displayed a severe proliferation deficit phenotype, which could be partially rescued by re-expression of human PC4. The reduced proliferation was not due to …