| To survive and prosper in pathogen-rich environments, insects have to rely on their innate immune system to fight against invading pathogens or parasites. Innate immunity is evolutionarily conserved from lower metazoans to mammals. Studies of insect defense mechanisms enhance our understandings of the human immune system and allow us to develop new strategies for controlling agricultural pests and arthropod vectors of human diseases.; Acute immune responses in insects are stimulated by pathogen-associated molecular patterns (PAMPs) including peptidoglycan (PG) from Gram-positive bacteria, lipopolysaccharide (LPS) from Gram-negative bacteria, and beta-1,3-glycan from fungi (Janeway and Medzhitov, 2002). A group of hemolymph proteins, designated pattern recognition receptors (PRRs), specifically bind to PAMPs. Molecular interactions between PAMPs and PRRs provoke systemic defense reactions such as phagocytosis, nodule formation, encapsulation, and synthesis of antimicrobial peptides (AMPS).; Prophenoloxidases (proPO) are present in both cuticle and hemolymph of insects. Their active forms, phenoloxidases (POs), catalyze the formation of quinones that are precursors of melanin (Ashida and Brey, 1998). Melanotic encapsulation is an effective mechanism to immobilize parasites. Quinones are toxic to invading microbes. They are also involved in cuticle sclerotization and wound healing. Proteolytic activation of proPO depends on a largely unknown serine proteinase (SP) cascade. The terminal enzyme of the cascade, proPO-activating proteinase (PAP), cleaves proPO. So far, three PAPs have been identified in the tobacco hornworm, Manduca sexta (Jiang et al., 1998; Jiang et al., 2003a; Jiang et al., 2003b). They contain 1 or 2 regulatory clip domain At least in some insects, PAP requires accessory protein(s) for generating active PO. Two clip-domain serine proteinase homologs ( M. sexta SPH-1 and SPH-2) function as a "cofactor" for the PAPs (Yu et al., 2003). The expression levels of PAPs and SPHs increase significantly after a bacterial challenge. To date, organization and expression of M. sexta PAP genes have not yet been studied.; My research aims to: (1) study the organization and transcriptional regulation of M. sexta PAP-1 and PAP-3 genes; (2) characterize M. sexta serpin-6 and its interaction with PAP-3; 3) produce D. melanogaster Spn43Ac and analyze its role in regulating immune SPs. (Abstract shortened by UMI.)... |
