Submitted to: Journal of Insect Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/6/2006
Publication Date: 3/31/2006
Citation: Margam, V.M., Gelman, D.B., Palli, S.R. 2006. Ecdysteroid titers and developmental expression of ecdysone-regulated genes during metamorphosis of the yellow fever mosquito, aedes aegypti (diptera: culicidae). Journal of Insect Physiology. 52:558-568. Interpretive Summary: The yellow fever mosquito transmits viruses that cause yellow fever, dengue fever, and other serious diseases. Although information is available on feeding, water regulation and reproduction of this insect, information about the hormonal regulation of development during the immature stages of mosquitoes is lacking. Changes in the level of the mosquito molting hormone during the last immature stages have been reported in the scientific literature, but results are contradictory. Thus, information as to the precise fluctuations of molting hormone levels during these stages is needed. In addition, in order to understand the regulatory functions of the molting hormone, it is necessary to determine when genes controlled by this hormone are expressed during mosquito development. In the current study, molting hormone levels were measured and the times of expression of molting hormone receptor genes and inducible genes were determined. Four molting hormone peaks in the last immature stages were observed, and expression of the various genes of interest typically occurred just before, during or slightly after one or both of the last two larval molting hormone peaks and the single pupal peak. By assaying every three hours, we were able to clarify the discrepancies in results reported previously, and to elucidate the relationship between molting hormone production and gene expression in regulating mosquito development. Our results will be very useful to other investigators and will contribute to understanding how the insect molting hormone controls mosquito development by regulating gene expression.
Technical Abstract: Ecdysteroid titers and expression profiles of ecdysone-regulated genes were determined during the last instar larval and during the pupal stages of Aedes aegypti (Diptera: Culicidae). Three peaks of ecdysteroids occurring at approximately 24, 30-33 and 45-48 hrs after ecdysis to the fourth instar larval stage were detected. In the pupa, a large peak of ecdysteroids occurred between 6-12 hrs after ecdysis to the pupal stage. A small rise in ecdysteroids was also detected at the end of the pupal stage. Quantitative reverse transcriptase polymerase chain reaction analyses of the expression of ecdysone receptors and ecdysone-regulated genes showed that the peaks of expression of most of these genes coincided with the rise in ecdysteroid levels during the last larval and pupal stages. In the last larval stage, ecdysteroid titers and mRNA expression profiles of ecdysone-regulated genes are similar to those observed for Drosophila melanogaster. However, in the early pupal stage, both ecdysteroid titers and the expression of ecdysone-regulated genes are somewhat different from those observed in D. melanogaster, probably because the duration of the pupal stage in D. melanogaster is 84 hrs while in Ae. aeqypti the duration is only 48 hrs. These data which describe the relationship between ecdysteroid titers and mRNA levels of Ae. aegypti ecdysteroid-regulated genes lay a solid foundation for future studies on the hormonal regulation of development in mosquitoes.