A PHOSPHORYLATION SITE in the FTZ HOMEODOMAIN IS REQUIRED for Segrnntation in DROSOPHILA
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A PHOSPHORYLATION SITE IN THE FTZ HOMEODOMAIN IS REQUIRED FOR SEGrnNTATION IN DROSOPHILA Jianli Dong A thesis submitted in conformity with the requirements r for the degree of Doctor of Philosophy Graduate Department of Molecular and Medical Genetics University of Toronto O Copyright by Jianli Dong 1999 National Library Biblioth&que nationale du Canada Acquisitions and Acquisitions et Bibliographic Services services bibliographiques 395 Wellington Street 395, rue Wellington Ottawa ON KIA ON4 OttawaON KlAON4 Canada Canada YOW m~ vam dnrrcnr00 Our Me Nolre dfdf~ll~~ The author has granted a non- L'auteur a accorde melicence non exclusive licence allowing the exclusive pennettant &la National Library of Canada to Bibliotheque nationale du Canada de reproduce, loan, distribute or sell reproduire, prster, distribuer ou copies of this thesis in microform, vendre des copies de cette these sous paper or electronic formats. la forme de microfiche/film, de reproduction sur papier ou sur format Bectronique. The author retains ownership of the L'auteur conserve la propriete du copyright in this thesis. Neither the droit d'auteur qui protege cette these. thesis nor substantial extracts fiom it Ni la these ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent Stre imphes reproduced without the author's ou autrement reproduits sans son permission. autorisation. A Phosphorylation site in the Ftz homeodomain is required for segmentation in Drosophila Doctor of Philosophy, 1999 Jianli Dong Department of Molecular and Medical Genetics University of Toronto Abstract The Drosophila homeodomain-containing protein Fushi tarazu (Ftz) is expressed sequentially in the embryo, first in alternate segments, then in specific neuroblasts and neurons in the central nervous system and finally in parts of the gut. During these different developmental stages, the protein is heavily phosphorylated on different subsets of Ser and Thr residues. This stage-specific phosphorylation suggests possible roles for signal transduction pathways in directing tissue-specific Ftz activities. The objective has been the testing of the importance of a single phosphorylation site for Ftz activity in the embryo. This was done by mapping Ftz phosphorylation sites, mutating the relevant Ser or Thr residues to Ala and Asp, and then testing the ability of the mutated proteins to rescuepz mutant embryos. My analysis has focused on T263, which is in the N-terminus of the Ftz homeodomain. This site is phosphorylated in vitro by Drosophila embryo extracts and by purified protein kinase A. In the embryo, mutagenesis of this site to the non-phosphorylatable residue Ala results in segmental defects. Conversely, replacement of T263 by Asp, which is also non-phosphorylatable, but which successfully mimics phosphorylated residues in a number of proteins, rescues the segmental phenotype. This suggests phosphorylation of Ftz on residue T263 is required for function in the ectoderm. In the CNS however, both T263A and T263D mutant proteins function normally, indicating that the requirement for T263 phosphorylation is stage-specific. In terms of molecular properties, mutation of T263 to Ala and Asp does not affect Ftz DNA binding activity in vim, nor do the mutations affect transcriptional activity in transfected S2 cells. I conclude that T263 phosphorylation is most likely required for a homeodomain-mediated interaction with an embryonically expressed protein. To Momand Dad Acknowledgments After I finish writing this lengthy dissertation, I am fully aware that this work of science and arts would not be completed without supports and contributions from many others whom I live and work with. I am most grateful to my husband for his consistent support. He always stands by my side whenever I need him. Without him, I even could not imagine how I could have gone through these six years full of joys and disappointments. I specidly thank my family members and relatives in China. They never stop delivering their blessings and encouragement from overseas. In particular, I wish to thank my Ph.D. advisor, Dr. Henry Krause. I learned a lot from him during my Ph.D. training. He is the most patient scholar I have ever known. He always has wise solutions to test tough hypotheses. I am grateful to my committee members: Drs. Andrew Spence, and Mike Tyers. They offered much valuable advice and many critical suggestions for my project. I appreciate Drs. Thomas Kornberg, Barbara Funnell, and Ulrich Tepass for taking time for my thesis defence. I would like to thank many people in the Drosophila community for their help. Drs. Daniel Kalderon, Ian Duncan, John Kiger, James Manley, Jim Japes, Andrew Travers, Michael Akam, and Manfred Frasch generously offered me fly lines, DNA constructs and antibodies. I thank Dr. Steve Mason for Drosophila embryo extracts and Dr. Laurent Rue1 for S2 cell phosphate-free medium. I also appreciate help from members of the people in the laboratory. Particularly, I would like to thank Ling-Hong Hung and Robert Strome for phosphoarnino acid analyses on Ftz T263,Andrzej Nasiadka for fly crosses and Andrew Sirnrnonds for computer support. Table of Contents Thesis Abstract ii Acknowledgments v Table of Contents vi List of Tables X List of Figures xi List of Appendices xii List of Abbreviations xiii Chapter 1: Introduction 1 1.1 Drosophila Embryogenesis and Segmentation 2 1.1.1 Drosophila Embryogenesis, a Brief Overview 2 1.1.2 Segment and Parasegment 7 1.1.3 Genetic Control of Drosophila Segmentation 8 1.2 Homeobox Genes and Homeodomain Proteins 14 1.2.1 Homeobox Genes in Animal Development 14 1.2.2 Classification of Horneobox Genes 16 1.2.3 Homeodomain Proteins are Transcription Factors 19 1.2.4 Regulation of Homeodomain proteins by Protein-protein Interactions 23 1.2.4.1 a2,Mcml and a1 1.2.4.2 HOMIHox and ExdIPbx 1.2.4.3 Exd and Hth 1.3 fishi tarazu, a Drosophila Homeobox Gene 1.3.1frz Expression and Function 1.3.2 Transcriptional Regulation of the& gene 1 -3.2.1 Cis-acting Transcription Elements 1.3.2.2 Trans-acting Factors 1.3.3 Regulation offtz mRNA and Protein Stability 1.3.3.1ftz mRNA Instability Elements 1.3.3.2 Ftz PEST Regions 1.3.4 Regulation of Ftz Activity by Protein-protein Interaction 1.3.4.1 Ftz and Prd 1.3.4.2 Ftz and Ftz-F1 1.4 Regulation of Transcription Factors by Phosphorylation 1.4.1 NF-KBhd3 and DorsaVCactus 1.4.2 CREB and CBP 1.4.3 Pit- 1 1.4.4 Phosphorylation of Ftz 1.5 Objectives and Overview of this Dissertation Chapter 2: A Phosphorylation Site in the Ftz Homeodomain is Required for Segmentation 61 2.0 Abstract 62 2.1 Introduction 63 2.2 Results 65 2.2.1 Ftz Phosphorylation by Embryo Extracts 65 2.2.2 In vivo Analysis of T263 Mutants 75 2.2.3 Cuticle Patterns 76 2.2.4ftz Autoregulation 79 2.2.5 en and wg Expression 84 2.2.6 DNA-binding Activity 84 2.2.7 Transcriptional Activity in Cultured S2 Cells 85 2.3 Discussion 90 2.3.1 Evidence for T263 Phosphorylation in vitro and in vivo 90 2.3.2 Stage Specificity of T263 Mutant Defects 90 2.3.3 Variability in the T263A Phenotype 91 2.3.4 Activities Affected by T263 92 2.3.5 Proteins that Interact with Ftz 93 2.3.6 Conservation of Thr263 94 2.3.7 Identity of the T263 Kinase 97 2.3.8 Homeodomain Proteins and Phosphorylation 2.4 Materials and Methods 2.4.1 Site-directed Mutagenesis and Construction of Ftz Expression Vectors 2.4.2 Expression and Partial Purification of Ftz Polypeptides 2.4.3 In vitro Kinase Assays 2.4.4 Phosphopeptide Mapping and Phosphoaminoacid Analysis 2.4.5 Construction of P-element Rescue Vectors 2.4.6 Cuticle Preparations, In situ Hybridization and Immunolocalization 2.4.7 Electrophoretic Mobility Shift Assays 2.4.8 Transient Transfection Assays Chapter 3: Tissue-specific Requirement for a Phosphorylation Site in the Fushi tarazu Homeodomain 104 3.0 Abstract 105 3.1 Introduction 106 3.2 ResuIts and Discussion 108 3.2.1 Ftz Thr263Ala Embryos Have Normal Eve Staining in RP2 Neurons 108 3.2.2 RP2 Neurons Are Unaffected in Ftz T263D-rescued Embryos 110 3.2.3 Tissue-specific Requirements for T263 Phosphorylation 110 3.2.4 What is the Cause of T263D Lethality? 112 3.2.5 Phosphorylation as a Means of Switching Tissure-specific Homeoprotein Activities 112 3.2.6 Molecular Functions of Ftz Affected by Thr263 f hosphorylation 113 3.3 Materials and Methods 113 3.3.1 Fly Strains 114 3.3.2 Embryo Collection, Fixation and Imnunostaining 114 Chapter 4: Discussion and Future Directions 4.1 Summary viii 4.2 Discussion 121 4.2.1 Ftz T263A is Defective in Segmentation 121 4.2.2 Ftz T263 Phosphorylation is not Required in the CNS 122 4.2.3 Molecular Consequences of Phosphorylation of Ftz T263 123 4.2.4 Is PKA the T263 Kinase? 125 4.2.5 Are Residues at Position 7 Phosphorylated in Other Homeodomains? 126 4.2.6 Multiple Levels of ftz Regulation 4.3 Future Directions 4.3.1 Identification of Proteins that Interact with Ftz and the Effect of Ftz T263 Phosphorylation on the Interaction 4.3.2 Analysis of the Effects of Mutations Affecting Other Ftz Phosphorylation Sites 4.4 Conclusion Appendix I: Effects of Ftz T263 Mutation on Protein-protein Interactions Introduction of Proteins Tested Results Discussion Materials and Methods Appendix 11: Sequence Alignment of Representative Homeodomain Classes References 151 List of Tables Table 1. Survival indices of Ftz T263 mutant offspring List of Figures Figure 1. Drosophila embryogenesis, stage 1 to 13 Figure 2.