List of Contents Abstract ··································································· i List of contents ······················································ ⅲ List of figures ························································· ⅴ Ⅰ. INTRODUCTION 1.1 Pheromone-mediated gene expression plasticity in C. elegans ············································································· 1 1.2 Pheromone-mediated developmental plasticity ·············· 2 Ⅱ. MATERIALS AND METHODS ······························· 5 Ⅲ. RESULTS 3.1 Neuropeptide signaling regulates pheromone-me diated gene expression of a chemoreceptor gene in C. elegans 3.1.1 Pheromone-mediated str-3 repression in the ASI chemosensory neurons was imposed from egg to the L1 larval stage ·· 16 3.1.2 Mutations in the pheromone receptor genes abolished pheromone- mediated regulation of str-3 gene expression ··········· 18 3.1.3 Food availability, internal feeding state, and ambient temperature did not affect str-3 expression ····························· 25 3.1.4 FLP-18 neuropeptide signaling was required for pheromonemediated regulation of str-3 gene expression via a NPR-1 neuropeptide receptor ························································· 27 3.1.5 Pheromone exposure did not exhibit abnormal chemotactic behavior ································································ 32 3.2 Neuropeptide signaling regulates pheromone-mediated gene expression of a chemoreceptor gene in C. elegans 3.2.1 crh-1 CREB mutants inappropriately form transient pre-daue L2d larvae ··························································· 34 3.2.2 L2d formation of crh-1 mutants is specifically induced by ascr#5 exposure even in plenty food supply ···················· 37 3.2.3 crh-1CREB mutants express a L2d marker gene in non-dauer ivinducing condition ················································· 39 3.2.4 crh-1 acts in the ASI neurons to regulate ascr#5-mediated L2d formation ···························································· 44 3.2.5 The DAF-7 TGF-β signaling pathway regulates ascr#5-medi ated L2d formation of crh-1 mutants ···························· 50 3.2.6 daf-7 expression is decreased in the ASI neurons of crh-1 mutants ······························································ 55 3.2.7 CRH-1 directly regulates daf-7 expression via a conserved CRE motif ··························································· 60 3.2.8 crh-1 may interact with several genes to mediate proper L2d formation ···························································· 64 Ⅳ. DISCUSSION ···················································· 66 Ⅴ. REFERENCES ··················································· 78 Ⅵ. SUMMARY IN KOREANS ··································· 81