Limits...
Embryonic desiccation resistance in Aedes aegypti: presumptive role of the chitinized serosal cuticle.

Rezende GL, Martins AJ, Gentile C, Farnesi LC, Pelajo-Machado M, Peixoto AA, Valle D - BMC Dev. Biol. (2008)

Bottom Line: It has been argued that mosquito SC contains chitin as one of its components, however conclusive evidence is still missing.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.With this embryological approach we expect to shed new light regarding this important physiological process related to the Ae. aegypti life cycle.

View Article: PubMed Central - HTML - PubMed

Affiliation: 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

ABSTRACT

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.

Conclusion: 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.

Show MeSH

Related in: MedlinePlus

Abrupt acquisition of desiccation resistance in Aedes aegypti embryogenesis is related to serosal cuticle formation. Pools of synchronized eggs at different embryonic ages were air-dried for 15 minutes (see items 2 and 3 of Methods). (A) The percentage of intact eggs was evaluated. Black arrow: end of embryogenesis. (B) 11-HAE and (C) 13-HAE eggs after 15 minutes air-exposure. The abrupt acquisition of impermeability between 11 and 13 hours of development is coincident with the appearance of the serosal cuticle, as determined by chlorine digestion (item 5 of Methods). (D) 11-HAE egg after 15 minutes exposure to chlorine. White dashed arrows: extrusion of cellular contents. (E) 13-HAE egg exposed to chlorine for 30 minutes. Note chorion almost complete disintegration. Black arrow: transparent serosal cuticle around the embryo. White arrows: reminiscent chorion.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2561029&req=5

Figure 1: Abrupt acquisition of desiccation resistance in Aedes aegypti embryogenesis is related to serosal cuticle formation. Pools of synchronized eggs at different embryonic ages were air-dried for 15 minutes (see items 2 and 3 of Methods). (A) The percentage of intact eggs was evaluated. Black arrow: end of embryogenesis. (B) 11-HAE and (C) 13-HAE eggs after 15 minutes air-exposure. The abrupt acquisition of impermeability between 11 and 13 hours of development is coincident with the appearance of the serosal cuticle, as determined by chlorine digestion (item 5 of Methods). (D) 11-HAE egg after 15 minutes exposure to chlorine. White dashed arrows: extrusion of cellular contents. (E) 13-HAE egg exposed to chlorine for 30 minutes. Note chorion almost complete disintegration. Black arrow: transparent serosal cuticle around the embryo. White arrows: reminiscent chorion.

Mentions: Quantification of desiccation resistance, performed through air exposure of differently aged eggs (Fig. 1, see items 2 and 3 of Methods for details), resulted in complete shrinkage of eggs up to 11 HAE (HAE = hours after egglaying) (Fig. 1A, B). In contrast virtually all the eggs 13 HAE or older remained intact (Fig. 1A, C). It should be note that in our conditions Ae. aegypti total embryonic development takes 61.5 hours at 28°C (Farnesi and Rezende, to be published elsewhere).


Embryonic desiccation resistance in Aedes aegypti: presumptive role of the chitinized serosal cuticle.

Rezende GL, Martins AJ, Gentile C, Farnesi LC, Pelajo-Machado M, Peixoto AA, Valle D - BMC Dev. Biol. (2008)

Abrupt acquisition of desiccation resistance in Aedes aegypti embryogenesis is related to serosal cuticle formation. Pools of synchronized eggs at different embryonic ages were air-dried for 15 minutes (see items 2 and 3 of Methods). (A) The percentage of intact eggs was evaluated. Black arrow: end of embryogenesis. (B) 11-HAE and (C) 13-HAE eggs after 15 minutes air-exposure. The abrupt acquisition of impermeability between 11 and 13 hours of development is coincident with the appearance of the serosal cuticle, as determined by chlorine digestion (item 5 of Methods). (D) 11-HAE egg after 15 minutes exposure to chlorine. White dashed arrows: extrusion of cellular contents. (E) 13-HAE egg exposed to chlorine for 30 minutes. Note chorion almost complete disintegration. Black arrow: transparent serosal cuticle around the embryo. White arrows: reminiscent chorion.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2561029&req=5

Figure 1: Abrupt acquisition of desiccation resistance in Aedes aegypti embryogenesis is related to serosal cuticle formation. Pools of synchronized eggs at different embryonic ages were air-dried for 15 minutes (see items 2 and 3 of Methods). (A) The percentage of intact eggs was evaluated. Black arrow: end of embryogenesis. (B) 11-HAE and (C) 13-HAE eggs after 15 minutes air-exposure. The abrupt acquisition of impermeability between 11 and 13 hours of development is coincident with the appearance of the serosal cuticle, as determined by chlorine digestion (item 5 of Methods). (D) 11-HAE egg after 15 minutes exposure to chlorine. White dashed arrows: extrusion of cellular contents. (E) 13-HAE egg exposed to chlorine for 30 minutes. Note chorion almost complete disintegration. Black arrow: transparent serosal cuticle around the embryo. White arrows: reminiscent chorion.
Mentions: Quantification of desiccation resistance, performed through air exposure of differently aged eggs (Fig. 1, see items 2 and 3 of Methods for details), resulted in complete shrinkage of eggs up to 11 HAE (HAE = hours after egglaying) (Fig. 1A, B). In contrast virtually all the eggs 13 HAE or older remained intact (Fig. 1A, C). It should be note that in our conditions Ae. aegypti total embryonic development takes 61.5 hours at 28°C (Farnesi and Rezende, to be published elsewhere).

Bottom Line: It has been argued that mosquito SC contains chitin as one of its components, however conclusive evidence is still missing.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.With this embryological approach we expect to shed new light regarding this important physiological process related to the Ae. aegypti life cycle.

View Article: PubMed Central - HTML - PubMed

Affiliation: 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

ABSTRACT

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.

Conclusion: 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.

Show MeSH
Related in: MedlinePlus