The Role of Iroquois 3 and 5 in Limb Bud Pattern Formation and Morphogenesis
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The Role of Iroquois 3 and 5 in Limb Bud Pattern Formation and Morphogenesis by Danyi Li A thesis submitted in conformity with the requirements for the degree of Doctor of Philosophy Graduate Department of Molecular Genetics University of Toronto © Copyright by Danyi Li (2014) The Role of Iroquois 3 and 5 in Limb Bud Pattern Formation and Morphogenesis Danyi Li Doctor of Philosophy Graduate Department of Molecular Genetics University of Toronto 2014 Abstract Limb skeletal pattern heavily relies on graded Sonic hedgehog (Shh) signaling. As a morphogen and growth cue, Shh regulates identities of posterior limb elements including the ulna/fibula and digits 2 through 5. In contrast, proximal and anterior structures including the humerus/femur, radius/tibia and digit 1 are regarded as Shh-independent and the mechanisms governing their pattern formation are unclear. Here I show that patterning of the proximal and anterior limb skeleton involves an early specification phase dependent on two transcription factors, Irx3 and Irx5 (Irx3/5). They are expressed in the anterior margin of the limb field to regulate expression of the key anterior prepattern gene Gli3 and specify the anterior population during limb initiation. The early specification phase is followed by a late modulation phase during which Shh signaling negatively regulates these anterior elements. In addition, Irx3/5 also play a role in limb bud morphogenesis. Irx3/5-DKO hindlimb buds are small with abnormal shape due to prolonged cell cycle time and division defects including anaphase bridge and altered cell division orientation in the anterior hindlimb field. Therefore, pattern formation of anterior limb skeletal elements requires functions of Irx3/5 during limb bud initiation for the specification and expansion of anterior population followed by negative modulation by Shh signaling. ii Acknowledgments I would like to take this opportunity to gratefully acknowledge the following people for their contributions and support throughout my graduate study. To my supervisors Dr. Chi-chung Hui and Dr. Sevan Hopyan, who gave me the chance to work on this exciting and challenging project and provide me with continuous guidance and opportunities to help me learn to be a scientist and become a better person, thank you for all the things that you have done for me. What you have taught me will benefit me in my future career and throughout my life. To my committee members Dr. Sabine Cordes and Dr. Andrew Spence, who gave me valuable comments and suggestions on my work, thank you for your attentiveness and scientific expertise. I am very lucky to work with a group of people who are always willing to help and make my time in the lab so enjoyable. To Mary Zhang, Rong Mo, Vijitha Puviindran and Kendra Sturgeon, thank you for your help from maintaining mouse colonies to mutant analysis and molecular experiments. I want to thank Dr. Rui Sakuma and Niki Vakili for initiating this project. To Olena Zhulyn, Wenqi Yin, Dr. Sue Li, Dr. Han Kim, Dr. Kelvin Law, Dr. Kimberly Lau, Dr. Steven Deimling, Dr. Hirotaka Tao and Laurie Wyngaarden, thank you for all the scientific and non-scientific discussions and sharing experience from experimental techniques to good food and sale discount. I especially thank Olena for helping with the flow cytometry experiment and brain storm on my manuscript development. I also want to thank Gregory Anderson from the Henkelman lab for collaboration on OPT analysis. I am also grateful to my family and friends who are always by my side cheering for my success and accomplishment and encouraging me to get through my “dark time”. iii Table of Contents Abstract ii Acknowledgment iii List of Tables vii List of Figures viii List of Videos x List of Abbreviations xi Chapter 1 INTRODUCTION 1 1 Introduction 1 1.1 An overview of vertebrate limb development and pattern formation 1 1.1.1 Limb induction 1 1.1.2 AER and limb PD pattern formation 2 1.1.3 ZPA and limb AP pattern formation 3 1.1.4 Self-regulated feedback loop between the AER and ZPA 4 1.1.5 Proliferative expansion, determination and differentiation 4 1.2 Limb AP pattern formation 5 1.2.1 Prepatterning the limb bud and Shh-activation network 5 1.2.2 Limb AP pattern formation after Shh activation 7 1.3 Cell biology of limb bud morphogenesis 9 1.3.1 Cell proliferation and cell death 9 1.3.2 Oriented cell behavior 10 1.4 Iroquois homeobox (Irx) genes 11 1.4.1 Discovery and genomic organization 11 1.4.2 Functions of Irx genes in development 12 1.4.3 Irx3 and Irx5 have novel functions in mouse hindlimb development 14 1.5 Thesis rational and outline 16 Chapter 2 Irx3/5 interact with Shh signaling for anterior limb pattern formation 22 2 Chapter 2 23 2.1 Summary 23 2.2 Introduction 23 2.3 Materials and Methods 24 2.3.1 Mice and genotyping 24 2.3.2 Cre activity induction via tamoxifen administration 25 2.3.3 Western blot 25 2.3.4 Cartilage staining 25 2.3.5 Quantification of limb bud frontal area plane 26 2.3.6 Section immunofluorescence 26 2.3.7 Whole-mount in situ hybridization 26 2.3.8 RNA isolation and real-time quantitative PCR 27 2.3.9 Chromatin immunoprecipitation 27 2.3.10 Quantification of location of Shh domain in limb buds and percentage of limb bud frontal plane area expressing Gli1 27 2.4 Results 28 2.4.1 Irx3/5 are required prior to limb bud outgrowth 28 iv 2.4.2 Irx3/5 regulate AP prepattern to promote proximal and anterior hindlimb progenitors 29 2.4.3 Irx3 binds to Gli3 limb enhancer and regulates Gli3 expression in hindlimb buds 30 2.4.4 Early genetic interaction between Irx3/5 and Gli3 is essential for signaling center establishment 31 2.4.5 Irx3/5-dependent anterior progenitor population contributes to preaxial polydactyly 32 2.4.6 Requirement of Irx3/5 in forelimb AP pattern formation is revealed in Kif7-/- background 32 2.4.7 Forelimb bud displays lower Shh signaling activity than that of the hindlimb 33 2.4.8 Reducing Shh signaling rescues anterior skeletal formation in the Irx3/5-DKO hindlimb 33 2.5 Discussion 34 2.5.1 A biphasic model for limb anterior pattern formation 34 2.5.2 Irx3/5 are key determinants of anterior population in early hindlimb field 35 Chapter 3 Limb bud morphogenesis requires regulation of cell proliferation by Irx3/5 in the anterior hindlimb field 49 3 Chapter 3 50 3.1 Summary 50 3.2 Introduction 50 3.3 Materials and Methods 52 3.3.1 Mice 52 3.3.2 OPT and limb bud morphology analysis 52 3.3.3 Double-pulse chasing analysis and cell cycle time estimation 52 3.3.4 Flow cytometry 53 3.3.5 Live imaging 53 3.3.6 Orientation of cell division 54 3.4 Results 54 3.4.1 Irx3/5-DKO hindlimb buds are small and display abnormal shape 54 3.4.2 Prolonged cell cycle time in the anterior hindlimb field of Irx3/5-DKO embryos during limb initiation 55 3.4.3 Live imaging data revealed multiple cell division defects in initiating Irx3/5-DKO hindimb buds 56 3.5 Discussion 57 Chapter 4 Conclusion and Future Experiments 68 4 Chapter 4 68 4.1 Thesis summary 68 4.2 Irx3 and Irx5 are novel anterior limb determinants 69 4.2.1 Identifying the molecular mechanism of anterior specification by Irx3/5 70 4.2.2 Fate mapping of Irx3/5-expressing cells may reveal the origin of anterior limb structures 72 4.3 Genetic interaction between Irx3/5 and Gli3 is required for signaling center establishment and limb outgrowth 74 4.4 Early specification and progressive modulation of anterior limb elements by Irx3/5 and Shh signaling 76 v 4.5 Difference between forelimb and hindlimb development 77 4.6 Irx3/5 regulate limb bud morphogenesis in multiple aspects 78 4.7 Conclusion remarks 79 References 84 vi List of Tables Table 3.1 Shape information of E10.0 forelimb buds 61 Table 3.2 Shape information of E10.0 and E10.5 hindlimb buds 61 vii List of Figures Figure 1.1 An overview of mouse limb bud outgrowth and AP pattern formation 18 Figure 1.2 Oriented cell behavior in limb bud morphogenesis 19 Figure 1.3 Iroquois homeobox genes 20 Figure 1.4 Expression of Irx3/5 during forelimb and hindlimb development 20 Figure 1.5 Irx3/5-DKO embryos display hindlimb specific phenotype 21 Figure 2.1 Irx3/5 are required prior to limb bud outgrowth for the formation of anterior-distal hindlimb elements 36 Figure 2.2 Morphogenesis, cell proliferation and cell death in Irx3/5-DKO hindlimb buds 37 Figure 2.3 Irx3/5 regulate hindlimb bud prepattern 38 Figure 2.4 Irx3/5-DKO hindlimb buds are primed to form Shh-responding elements 39 Figure 2.5 Irx3/5 regulate Gli3 expression in limb 40 Figure 2.6 Early genetic interaction between Irx3/5 and Gli3 is required for signaling center establishment and limb bud outgrowth 41 Figure 2.7 Irx3/5-dependent anterior progenitor population contributes to preaxial polydactyly 42 Figure 2.8 Irx3/5 are required for the formation of anterior forelimb elements in Kif7-/- background 42 Figure 2.9 Irx3/5 are involved in forelimb development 43 Figure 2.10 Shh domain is more posteriorly restricted in the forelimb bud than hindlimb 44 Figure 2.11 Forelimb bud displays lower Shh signaling activity than that of the hindlimb 45 Figure 2.12 Reducing Shh signaling in Irx3/5-DKO hindlimb buds rescues anterior pattern formation 46 Figure 2.13 Prepattern and limb bud size are not rescued in Irx3/5-DKO;Shh+/- hindlimbs 47 Figure 2.14 A biphasic model of limb anterior pattern formation 47 Figure 3.1 Surface renderings of E10.5 control and Irx3/5-DKO embryos viewed from the right 60 Figure 3.2 Dorsal and lateral views of forelimb bud isosurfaces at E10.0 61 Figure 3.3 Dorsal and lateral views of hindlimb bud isosurfaces at E10.0 and