Increased Insulin Signaling in Fat Body of Aedes Aegypti Mosquitoes Enhance Lifespace

Abstract

The mosquito Aedes aegypti is a well known vector of many viral diseases such as yellow fever, dengue and dengue hemorrhagic fever (DHF). In particular, dengue and DHF, though normally considered tropical diseases, are steadily increasing in prevalence throughout the world with cases being reported as far north as the Texas-Mexico border and in Florida. There is currently no vaccine for these diseases and vector control has proved challenging due to the urban preferences of A. aegypti. The insulin/insulin-growth factor signaling (IIS) pathway may provide an endogenous solution to vector control. In mosquitoes, the IIS plays an important role in the regulation of many physiological processes, including longevity and reproduction. Studies in several species, including Drosophila melanogaster, Caenorhabolitis elegans and Anopheles stephensi, have shown that decreasing insulin signaling leads to an increase in longevity [Hwangbo et al., 2004; Kimura et al., 1997]. Inversely, similar studies have shown that increasing insulin signaling results in a shortened lifespan and often an increase in reproduction [Corby-Harris et al., 2010]. Here we aimed to increase insulin signaling in the fat body of Aedes aegypti mosquitoes by creating a transgenic line that expresses an active form of Akt, a key component of the IIS, specifically in the fat body tissue. We observed the effects on longevity and reproduction in both a heterozygous and a homozygous line. However, contrary to the expected results, we observed an increase in the lifespan of heterozygous females positive for the transgene. We also observed no significant difference in the reproductive potential of heterozygous positive versus heterozygous negative females, although expression of vitellogenin was increased. This led us to consider the possibility that under these conditions insulin signaling may have been down-regulated or shut off completely, instead of being up-regulated as was expected. Further investigations need to be made into the possible causes of these results.