Embryonic desiccation resistance in Aedes aegypti: presumptive role of the chitinized Serosal Cuticle

We observed an abrupt acquisition of desiccation resistance during Ae. aegypti embryogenesis associated with serosal cuticle secretion, occurring at complete germ band extension, between 11 and 13 hours after egglaying. After SC formation embryos are viable on dry for at least several days. The presence of chitin as one of the SC constituents was confirmed through Calcofluor and WGA labeling and chitin quantitation. The Ae. aegypti Chitin Synthase A gene (AaCHS1) possesses two alternatively spliced variants, AaCHS1a and AaCHS1b, differentially expressed during Ae. aegypti embryonic development. It was verified that at the moment of serosal cuticle formation, AaCHS1a is the sole variant specifically expressed.In addition to the peritrophic matrix and exoskeleton, these findings confirm chitin is also present in the mosquito serosal cuticle. They also point to the role of the chitinized SC in the desiccation resistance of Ae. aegypti eggs. AaCHS1a expression would be responsible for SC chitin synthesis. With this embryological approach we expect to shed new light regarding this important physiological process related to the Ae. aegypti life cycle.The mosquito Aedes aegypti is the main dengue vector. One of the major problems concerning dengue transmission is that Ae. aegypti eggs resist desiccation, surviving several months under dry conditions in a dormancy state at the end of their embryonic development [1-3]. An important component of the desiccation resistance is the serosal cuticle (SC), a layer covering the embryo that is synthesized at early embryogenesis [4-7] (for review see [2]). The serosal cuticle is secreted by the serosa, a membrane formed by extra-embryonic cells that surrounds the whole embryo of many insects [2,8-11]. Upon oviposition, the mosquito eggshell is composed of two layers, a compound exochorion and a smooth endochorion [12]. The SC develops during embryogenesis and becomes the third eggshell layer, lying beneath the endochorion [2,4]. It sh