Mosquitoes generate an enormous burden on human health worldwide. Disease-transmitting species use a reproductive strategy, termed anautogeny, that requires a blood meal to initiate egg maturation. Whereas this strategy is important for driving disease transmission, the molecular mechanisms underlying this phenomenon are still poorly understood. The production of yolk protein precursors (YPPs), a central event in egg maturation, is called vitellogenesis. YPPs are synthesized in the fat body, the insect analogue of the vertebrate liver. Mosquito vitellogenesis is regulated by the steroid hormone 20 hydroxyecdysone (20E). However, 20E alone is not capable of activating vitellogenesisin vivo. Here, we report that amino acid signaling through the nutrient-sensitive target of rapamycin (TOR) pathway is essential for the activation of YPP gene expression. An increase in extracellular amino acid levels, similar to the increase observed after a blood meal, is critical for 20E stimulation of YPP gene expression. Treatment with the TOR kinase inhibitor rapamycin significantly inhibits YPP expression. We used RNA interference to knockdown the expression of two key proteins of the TOR signaling pathway, TOR, and tuberous sclerosis complex 2. Knockdown of TOR inhibited amino acid stimulation while knockdown of tuberous sclerosis complex 2, a negative regulator of TOR signaling, resulted in enhanced YPP expression. Thus, amino acid-based TOR signaling regulates the activation of egg development after a blood meal, an adaptation to the unique life style of mosquitoes.

Anautogenous mosquito females require a meal of vertebrate blood in order to initiate the production of yolk protein precursors by the fat body. Yolk protein precursor gene expression is tightly repressed in a state-of-arrest before blood meal-related signals activate it and expression levels rise rapidly. The best understood example of yolk protein precursor gene regulation is the vitellogenin-A gene (vg) of the yellow fever mosquito Aedes aegypti. Vg-A is regulated by (1) juvenile hormone signaling, (2) the ecdysone-signaling cascade, (3) the nutrient sensitive target-of-rapamycin signaling pathway, and (4) the insulin-like peptide (ILP) signaling pathway. A plethora of new studies have refined our understanding of the regulation of yolk protein precursor genes since the last review on this topic in 2005 (Attardo, Hansen et al. 2005). This review summarizes the role of these four signaling pathways in the regulation of vg-A and focuses upon new findings regarding the interplay between them on an organismal level.

The bed bug,Cimex lectularius, has re-established itself as a ubiquitous human ectoparasite throughout much of the world during the past two decades. This global resurgence is likely linked to increased international travel and commerce in addition to widespread insecticide resistance. Analyses of theC. lectulariussequenced genome (650 Mb) and 14,220 predicted protein-coding genes provide a comprehensive representation of genes that are linked to traumatic insemination, a reduced chemosensory repertoire of genes related to obligate hematophagy, host–symbiont interactions, and several mechanisms of insecticide resistance. In addition, we document the presence of multiple putative lateral gene transfer events. Genome sequencing and annotation establish a solid foundation for future research on mechanisms of insecticide resistance, human–bed bug and symbiont–bed bug associations, and unique features of bed bug biology that contribute to the unprecedented success ofC. lectulariusas a human ectoparasite.

Female mosquitoes are effective disease vectors, because they take blood from vertebrate hosts to obtain nutrients for egg development. Amino acid signaling via the target of rapamycin (TOR) pathway has been identified as a key requirement for the activation of egg development after a blood meal. We report the characterization of the TOR kinase and one of its major downstream targets, S6 kinase, of the yellow fever mosquito Aedes aegypti during egg development in adult females. Both TOR and S6K mRNA are expressed at high levels in the ovaries and in lower levels in fat body and other tissues. After a blood meal, the subcellular localization of TOR shifts from the cytoplasm to the plasma membrane of fat body cells. By detecting phosphothreonine 388 of mosquito S6 kinase, we show that TOR activity strongly increases in fat body and ovaries after a blood meal in vivo. Furthermore, phosphorylation of S6 kinase increases in in vitro cultured fat bodies after stimulation with amino acids. This increase is sensitive to the TOR inhibitor rapamycin in a concentration-dependent manner but not to the phosphatidylinositol 3-kinase/phosphatidylinositol 3-kinase-related kinase inhibitor LY294002, the MAPK inhibitor PD98059, or the translational inhibitor cycloheximide. RNA interference-mediated reduction of S6 kinase strongly inhibits the amino acid-induced up-regulation of the major yolk protein vitellogenin in vitro and effectively disrupts egg development after a blood meal in vivo. Our data show that TOR-dependent activation of S6 kinase is a central step in the transduction of nutritional information during egg development in mosquitoes.