Embryonic desiccation resistance in Aedes aegypti: presumptive role of the chitinized serosal cuticle.
BACKGROUND
One of the major problems concerning dengue transmission is that embryos of its main vector, the mosquito Aedes aegypti, resist desiccation, surviving several months under dry conditions. The serosal cuticle (SC) contributes to mosquito egg desiccation resistance, but the kinetics of SC secretion during embryogenesis is unknown. It has been argued that mosquito SC contains chitin as one of its components, however conclusive evidence is still missing.


RESULTS
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.


CONCLUSIONS
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.
Rezende
Gustavo Lazzaro
GL
Laboratório de Fisiologia e Controle de Artrópodes Vetores, Instituto Oswaldo Cruz, FIOCRUZ and Laboratório de Entomologia, Instituto de Biologia do Exército, Rio de Janeiro, Brazil. rezendeg@ioc.fiocruz.br
Martins
Ademir Jesus
AJ
Gentile
Carla
C
Farnesi
Luana Cristina
LC
Pelajo-Machado
Marcelo
M
Peixoto
Alexandre Afrânio
AA
Valle
Denise
D
D000330:Aedes / Q000737:chemistry / Q000196:embryology* / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002686:Chitin / Q000737:chemistry / Q000502:physiology*; D002687:Chitin Synthase / Q000096:biosynthesis / Q000235:genetics; D003715:Dengue / Q000635:transmission; D003890:Desiccation; D004527:Egg Proteins / Q000737:chemistry / Q000235:genetics; D005260:Female; D019476:Insect Proteins / Q000737:chemistry / Q000235:genetics; D008969:Molecular Sequence Data; D010063:Ovum / Q000737:chemistry / Q000254:growth & development*; D012326:RNA Splicing; D013997:Time Factors
D004527:Egg Proteins; D019476:Insect Proteins; C047663:cuticle proteins, insects; D002686:Chitin; D002687:Chitin Synthase
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