THE GUIDANCE FUNCTIONS OF UNC-6/NETRIN IN C. ELEGANS

다국어 초록 (Multilingual Abstract)

To understand the molecular mechanisms that direct the circumferential migrations in C. elegans, I examined the guidance functions of UNC-6. UNC-6 is a member of the netrin family of extracellular proteins. During development, cells and axons migrate towards or away from netrin sources depending on the guidance receptors, UNC-40/DCC and UNC-5. In order to test the tissue- and direction-specific guidance function of UNC-6, I analyzed dorsally and ventrally migrating cells and axons when UNC-6 derivatives lacking specific domain were expressed in unc-6 null mutants. I found that specific UNC-6 domains are required for distinct UNC-6 functions. UNC-6 domains V-2 and V-3 are required for dorsal migrations. UNC-6 domain VI is required for all functions, as is a small 8 amino acid region within the domain. unc-6ΔVI animals show more severe defects in the ventral migrations, suggesting that the remaining domains may interfere with the ventral guidance activities of another guidance receptors. I found that domain C is not required for the guidance functions, but has a role in inhibition of axon branching. My works describe the first in vivo functional analysis of the UNC-6/Netrin domains.
I also show that integrins participate in the UNC-6 guidance functions together with the UNC-40 receptor. I found allele-specific genetic interactions between integrin genes and the unc-6 and unc-40 genes. My results suggest that INA-1 integrin and UNC-40/DCC are working in the same pathway, likely as a part of receptor complex to interact with the netrin UNC-6 guidance cue. This study shows how extracellular guidance signals work through the modification of cytoskeletal dynamics to direct axon and cell migrations.

목차 (Table of Contents)

• Abstract = 1
• Acknowledgements = 3
• Dedication = 4
• Table of Contents = 5
• List of Tables = 7
• List of Figures = 8
• Chapter 1. Introduction = 11
• General Mechanisms of Axon Guidance = 11
• The UNC-40/DCC and UNC-4/Netrin pathway = 12
• Ephrins and Eph receptors = 17
• Slits and SAX-3/Robos = 19
• Integrins = 21
• Chapter 2. Analysis of the Functional Roles of Netrin UNC-6 Domains in C. elegans = 30
• Abstract = 30
• Introduction = 32
• Materials and Methods = 35
• Results = 42
• Discussion = 50
• Chapter 3. Netrin UNC-6 and the Regulation of Branching and Extension of Motoneuron Axons from the Ventral Nerve Cord of Caenorhabditis elegans = 72
• Abstract = 72
• Introduction = 73
• Materials and Methods = 78
• Results = 83
• Discussion = 93
• Chapter 4. A Role for Integrins in Netrin UNC-6 Guidance Functions of C. elegans = 118
• Abstract = 118
• Introduction = 119
• Materials and Methods = 121
• Results = 125
• Discussion = 133
• Chapter 5. General Discussion = 148
• Functions of UNC-6 Domains in Circumferential Guidance = 148
• A Role for Integrins in Circumferential Guidance = 152
• General Model = 156
• References = 162
• Curriculum Vitae = 180