BIOCHEMISTRY OF EGG CHORION TANNING IN MOSQUITOES

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Quinone-mediated protein cross-linking reactions are extremely important biochemical events within the Class Insecta. These reactions contribute to mechanisms of cuticular tanning, melanotic encapsulation defense reactions, wound healing, and the hardening of the egg shell in numerous groups of insects. All of these processes are critical to the survival and reproductive success of insects. There is an obvious biochemical relationship between these physiological events, and increasing our understanding of the mechanisms controlling these reactions in mosquito vectors could have a significant impact on future efforts to negatively interfere with vector survival through new and innovative control strategies. The objective of the research proposed herein is to clarify the biochemical processes required for the successful formation and hardening of the egg chorion in the mosquito, Aedes aegypti. Various biochemical as well as molecular techniques will be used to (l) assess the roles specific enzymes play in the formation and hardening of the chorion, (2) determine the role tyrosine and catecholamines might play in quinone cross-linking and melanization of the mosquito egg chorion, (3) clarify the mechanisms involved in the peroxidase-mediated protein crosslinking reactions within developing eggs of A. aegypti, and (4) assess the site of synthesis of dopa decarboxylase and peroxidase as these relate to the formation of the chorion and to evaluate the genetic regulation of these enzymes. A better knowledge of the physiology and biochemistry of chorion formation in mosquitoes is critical to a thorough understanding of reproductive processes in this important group of disease vectors. Survival of eggs for extended periods of exposure to adverse environmental conditions, as is required for floodwater mosquitoes, is critically dependent on this biochemical process. Therefore, the proposed studies will provide essential information for a more thorough understanding of the biological events and consequences of chorion formation and hardening. Because the biochemistry of melanization and quinone tanning required for the hardening of the egg chorion likely shares similarities with the biochemical events necessary for cuticular tanning and parasite encapsulation, a better understanding of egg chorion tanning in mosquitoes also might provide insight into these important physiological events.