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The Neurobiology of C. elegans assembles together a series of chapters describing the progress researchers have made toward solving some of the major problems in neurobiology with the use of this powerful model organism. The first chapter is an introduction to the anatomy of the C. elegans nervous system. This chapter provides a useful introduction to this system and will help the reader who is less familiar with this system understand the chapters that follow. The next two chapters on learning, conditioning and memory and neuronal specification and differentiation, summarize the current state of the C. elegans field in these two major areas of neurobiology. The remaining chapters describe studies in C. elegans that have provided particularly exciting insights into neurobiology.
The UNC-6/netrin pathway plays an important role in cell migration and axon guidance. Ventral sources of UNC-6 guide axons from the ventral to dorsal surface by activating the repulsive UNC-5 receptor and UNC-40 co-receptor, and from dorsal to ventral by activating the attractive UNC-40 receptor. In C. elegans, UNC-129 is a TGF-beta family member expressed in dorsal body wall muscles and is thought to promote the interaction between UNC-5 and UNC-40 for long range repulsion away from ventral sources of UNC-6, while inhibiting UNC-5-alone function. The promotion of UNC-5+UNC-40 signaling could act to increase sensitivity where the UNC-6/netrin concentration is relatively low away from its source. unc-130 encodes a transcription factor that represses expression of unc-129 ventrally. In an unc-130(ev505) mutant, UNC-129 is ectopically expressed, effectively abolishing the gradient of UNC-129 causing migration and axon guidance defects. This project aims to provide better understanding of the UNC-129 pathway by 1) investigating potential UNC-129 receptors and 2) characterizing suppressors of ectopic UNC-129 function. PUR-7 is a candidate UNC-129 receptor discovered in silico that shares similarity to the extracellular domain of canonical TGF-beta receptors. A deletion of genomic DNA that deletes pur-7 and part of the neighbouring srd-4 gene enhances the distal tip cell migration and axon guidance defects of a hypomorphic unc-5 allele, and enhances the migration defects of the unc-130 mutant. Efforts to disentangle the genetic interaction of pur-7 from srd-4 were unfortunately not fruitful. The sup7-2 mutant suppresses distal tip cell migration defects in the unc-130(ev505) mutant, suggesting a role in the UNC-129 pathway. Using mapping and bioinformatical analysis, sup7-2 was located to a genomic region between 5-6 Mb on chromosome X. There are mutations in five candidate genes in this region: ifa-4, tbc-7, gakh-1, actl-1 and C03B1.1. RNAi knockdown of gakh-1 and tbc-7 have an effect on unc-130(ev505) DTC migration defects. Injection of fosmids containing tbc-7 rescue the suppression by sup7-2. Although tbc-7 is likely the sup-7-2 gene, both candidates have an effect on DTC migration and are of interest for future study.