UNDERSTANDING MOLECULAR MECHANISMS REGULATING THE INITIAL SHELL-HARDENING PROCESS OF THE BLUE CRAB CALLINECTES SAPIDUS: INVOLVEMENT OF PROPHENOLOXIDASE AND THE TANNING HORMONE BURSICON
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Phenoloxidase, the integral enzyme for the prophenoloxidase cascade system in insects and crustaceans is essential in the melanization of pathogens and wound healing. Upon proteolytic activation of the zymogen prophenoloxidase, the active enzyme phenoloxidase catalyzes phenol substrates to sclerotize the protein matrix of arthropod cuticles. The hard exoskeleton protects and supports the body of crustaceans; however, it presents several challenges to continuous growth. To grow, crustaceans must periodically molt by shedding their exoskeletons (ecdysis). Ecdysis is triggered by the action of a set of hormones, which also initiate the previous deposition of a new soft cuticle beneath the hard exoskeleton. The flexible and soft new cuticle is expanded by the isosmotic intake of water during and immediately after ecdysis. Animals can then display their molt-related somatic growth. At the same time the unarmored crustaceans undergo the concurrent shell-hardening process to build a new exoskeleton.
In crustaceans, the molecular and physiological mechanisms involved in the initial shell hardening process have been poorly understood compared to the corresponding process in insects. This dissertation addresses the molecular mechanisms which regulate the initial shell-hardening process of crustaceans, using the blue crab Callinectes sapidus as research model. To this end, the research focuses on the hemocyte prophenoloxidase and the neurohormone bursicon to define their roles and interactions in the regulation of the initial shell-hardening. A differential expression of prophenoloxidase in hemocytes is found and the role of prophenoloxidase in the shell-hardening process of crustacean is established. Unraveling the shell-hardening process of C. sapidus will add our understanding of the molt-related somatic growth of this and other economically valuable decapod crustacean species. This knowledge may contribute to increases in productivity of crustacean fisheries and aquaculture by the development of biotechnology to extend or reduce the soft-shell stage of crustaceans.