Wnt Signaling regulates Q Neuroblast Cell Polarization and Migration in Caenorhabditis elegans

Neuronal migration is an essential process that establishes the intricate and precise connectivity of the nervous system. Here, we study the molecular mechanisms of neuronal migration, using Q neuroblast lineages in C.elegans as a model. The left and right Q neuroblasts are equivalent lineages that show distinct migratory patterns along the antero-posterior axis. The Q descendants on the left (QL) migrate posteriorly, whereas those on the right (QR) migrate anteriorly. The posterior QL descendant migration requires the EGL-20/Wnt-dependent Hox gene mab-5. mab-5 repressed another Hox gene, lin-39, whose expression would otherwise promote anterior migration. In addition to this transcriptional regulation, another Wnt CWN-1 and Frizzled receptor MOM-5 promote QR anterior migration. We found that CWN-1/MOM-5 and LIN-39 act in parallel to promote Q cell anterior migration. CWN-1 instructed QR.pa anterior polarization and also influences the polarization of QL.pa that lacked EGL-20/MAB-5 signaling. We show that the Frizzleds MIG-1 and MOM-5 were expressed and functioned autonomously in the QL and QR descendants. Furthermore, we found that the planar cell polarity gene vang-1, which is the C. elegans homolog of the mammalian Vangl2 and Drosophila van Gogh/Strabismus, strongly suppressed QL anterior migration in the mig-1 mutant, and improved QR undermigration in the cwn-1 or egl-20 mutants. These data suggest that PCP genes regulate the Q cell migration.論文審定書 i TABLE OF CONTENTS ii ACKNOWLEDGEMENT iv 中文摘要 v ABSTRACT vi I. INTRODUCTION 1 1.1 Neuronal migration 1 1.2 Wnt signaling 3 1.3 Q neuroblast migration in C. elegans 4 II. MATERIALS AND METHODS 7 2.1 C.elegans Genetics 7 2.2 Plasmid Construction 8 2.3 Germline Transformation 9 2.4 Synchronization and Staging in Q cell Observation 9 2.5 LIN-39 Quantification 10 2.6 Q cell Polarization Analysis 11 2.7 Quantification of AVM and PVM Positions 11 III. RESULTS 12 3.1 LIN-39 Expression in the Q Lineages Was Independent of CWN-1 Signaling 12 3.2 cwn-1 and mom-5 Promote Q.pa Anterior Polarization 14 3.3 The Frizzleds MIG-1 and MOM-5 Function Autonomously to Regulate Q Cell Polarization 17 3.4 vang-1/van Gogh Antagonizes Wnt Signaling 18 IV. DISCUSSION 22 V. FIGURES 26 Figure 1. Development of the Q Neuroblast Lineages in C. elegans 26 Figure 2. Examples of Wnt Pathways in C. elegans and in Mammals 28 Figure 3. LIN-39 Expression in the QL Lineage. 30 Figure 4. LIN-39 Expression in the QR Lineage. 32 Figure 5. Quantification of Migratory Q.pa Cell Polarization. 34 Figure 6. Polarity Index in the QL.pa Cells 36 Figure 7. Polarity Index in the QR.pa Cells 38 Figure 8. Ectopic CWN-1 Expression Patterns of twnEx113, twnEx114, and twnEx162 40 Figure 9. CWN-1 Expression Patterns Induced by Heat Shock 42 Figure 10. The Polarity Indeces of QL.pa and QR.pa in Animals with Various cwn-1 Transgenes. 44 Figure 11. mom-5 Expression Patterns 46 Figure 12. mom-5 Was Expressed in the Q Lineages. 48 Figure 13. MOM-5 Overexpression Disrupted Q Cell Migration. 50 Figure 14. mig-1 Was Expressed in the Q Lineages. 52 Figure 15. mig-1 Functioned Autonomously in the Q Lineage 54 Figure 16. The vang-1 Mutation Rescued the PVM Mismigration in the mig-1 Mutant 56 Figure 17. The vang-1 Mutation Rescued AVM undermigration in the cwn-1 or the egl-20 Mutants 58 Figure 18. The vang-1 Mutation did not Rescue the QL.pa Polarization Defects of the mig-1 Mutant 60 Figure 19. The arr-1/arrestin1 Mutation Suppressed the PVM Defects of the mig-1 but not the mab-5 Mutants. 62 Figure 20. Model for how two Wnt signals Differentially Regulate Q Cell Migration 64 Table 1. List of primers for construct cloning 66 VI. REFERENCE 68 Appendix I. Cell position of QR.paa and QR.pap Normaski scoring in L1 animals 72 Appendix II. Cell position of QL.paa and QL.pap Normaski scoring in L1 animals 7