We present a draft sequence of the genome of Aedes aegypti, the primary vector for yellow fever and dengue fever, which at ~1.38 Gbp is ~5-fold larger in size than the genome of the malaria vector, Anopheles gambiae. Nearly 50% of the Aedes aegypti genome consists of transposable elements. These contribute to a ~4-6 fold increase in average gene length and the size of intergenic regions relative to Anopheles gambiae and Drosophila melanogaster. Nevertheless, chromosomal synteny is generally maintained between all three insects although conservation of orthologous gene order is higher (~2-fold) between the mosquito species than between either of them and fruit fly. Three methods have provided transcriptional evidence for 80% of the 15,419 predicted protein coding genes in Aedes aegypti. An increase in genes encoding odorant binding, cytochrome P450 and cuticle domains relative to Anopheles gambiae suggests that members of these protein families underpin some of the biological differences between them.

Juvenile hormone (JH) plays crucial roles in many aspects of insect life. The Methoprene-tolerant (Met) gene product, a member of the bHLH-PAS family of transcriptional regulators, has been demonstrated to be a key component of the JH signaling pathway. However, the molecular function of Met in JH-induced signal transduction and gene regulation remains to be fully elucidated.Here we show that a transcriptional coactivator of the ecdysteroid receptor complex, FISC, acts as a functional partner of Met in mediating JH-induced gene expression. Met and FISC appear to use their PAS domains to form a dimer only in the presence of JH or JH analogs. In newly emerged adult female mosquitoes, expression of some JH responsive genes is considerably dampened when Met or FISC is depleted by RNAi. Met and FISC are found to be associated with the promoter of the early trypsin gene (AaET) when transcription of this gene is activated by JH. A juvenile hormone response element (JHRE) has been identified in the AaET upstream regulatory region and is bound in vitro by the Met-FISC complex present in the nuclear protein extracts of previtellogenic adult female mosquitoes. In addition, the Drosophila homologs of Met and FISC can also use this mosquito JHRE to activate gene transcription in response to JH in a cell transfection assay. Together, the evidence indicates that Met and FISC form a functional complex on the JHRE in the presence of JH and directly activate transcription of JH target genes.development | endocrinology | chromatin immunoprecipitation J uvenile hormones (JHs) are sesquiterpenoid molecules synthesized and secreted by the corpora allata in insects. JHs are essential for development, reproduction, diapause, caste differentiation, migratory behavior, and longevity in many insect species (1-4). The prominent role of JH is maintaining the status quo in juvenile insects and preventing an insect from precociously turning into an adult. During larval development, ecdysone (the molting hormone) causes larval-larval molts in the presence of JH in the hemolymph. After the corpora allata stop secreting JH in the final larval instar, insect tissues change their commitment, and ecdysone triggers the larval-pupal and pupaladult molts (5).JH appears to harness a variety of signal transduction pathways to exert its function. Some effects of JH are mediated via membrane receptors and the protein kinase C signaling pathway (4, 6), whereas more evidence suggests that JH acts through intracellular receptors to modulate gene expression (7-10). In some cases, JH seems to exert its functions by modulating the ecdysteroid signaling pathway (11-17).A leading candidate for the JH receptor (or a component of the receptor) is the product of the Methoprene-tolerant (Met) gene, which was originally isolated in Drosophila melanogaster (18). Met belongs to the basic helix-loop-helix (bHLH)-PerArnt-Sim (PAS) family of transcription factors that also includes the hypoxia inducible factor 1α (HIF-1α), aryl hydrocarbon receptor (AhR), aryl hydrocarbon ...

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In anautogenous mosquitoes, vitellogenesis, which includes production of yolk protein precursors, requires blood feeding. Consequently, mosquitoes transmit many diseases. Understanding the molecular mechanisms of vitellogenesis regulation will contribute significantly to vector control strategies. Newly emerged Aedes aegypti females require 3 days before becoming competent to activate vitellogenesis in response to a blood-meal-initiated, elevated titer of 20-hydroxyecdysone (20E). An orphan nuclear receptor gene ␤FTZ-F1 is transcribed in the fat body of newly emerged mosquito females; however, the ␤FTZ-F1 protein is only found 3 days later. Dramatically increased titer of the juvenile hormone III (JH III) is essential for the acquisition of 20E competence. In vitro fat body culture experiments have shown that ␤FTZ-F1 protein appears after exposure to JH III. Injection of double-stranded RNA complementary to ␤FTZ-F1 into newly emerged females attenuated expression of the early genes EcR-B, E74B, and E75A and the target YPP gene Vg, in response to a blood meal. Thus, ␤FTZ-F1 is indeed the factor defining the acquisition of competence to 20E in the mosquito fat body. Moreover, this is achieved through JH III-mediated posttranscriptional control of ␤FTZ-F1.I n oviparous animals, vitellogenesis is a key event in egg maturation, which involves the production of yolk protein precursors (YPPs) predominantly by extraovarial tissues and their uptake by developing oocytes. Numerous signals are involved in a precise coordination of vitellogenic tissues. In anautogenous mosquitoes, initiation of vitellogenesis requires a blood meal. As a consequence, mosquitoes are vectors of many devastating infectious diseases, including malaria, dengue fever, and lymphatic filariasis (1-4). Unraveling the molecular mechanisms of vitellogenesis regulation will aid the development of new strategies for more efficient vector control.In the yellow fever mosquito Aedes aegypti, blood feeding triggers a signaling cascade culminating in the elevation of titers of ecdysteroids, which is closely correlated with the production of YPPs in the fat body, a tissue functionally analogous to vertebrate liver (5-7). Also, the genes encoding two major YPPs, vitellogenin (Vg) and vitellogenic carboxypeptidase (VCP), are activated in fat bodies cultured in vitro on addition of the physiologically active ecdysteroid 20-hydroxyecdysone (20E), which suggests that the Vg and VCP genes are regulated by this hormone (8).The steroid hormone 20E controls larval molting and metamorphosis in many insects, and it functions during embryonic development and adult reproduction. The molecular mechanism of 20E action has been dissected in detail during Drosophila metamorphosis (9). As 20E titers are rising and dropping again, unique sets of genes are turned on and off at distinct stages. Additional factors are therefore essential for the achievement of such a precise control of gene expression. For instance, cuticle proteins, a major component of the insect exoskeleton, are...

Methoprene-tolerant (Met) protein is a juvenile hormone (JH) receptor in insects. JH-bound Met forms a complex with the βFtz-F1-interacting steroid receptor coactivator (FISC) and together they regulate JH response genes in mosquitoes. Both proteins contain basic-helix-loop-helix (bHLH) and PAS motifs. Here we demonstrated that FISC is the obligatory partner of Met for binding to JH-response elements (JHREs). Met or FISC alone could not bind a previously characterized JHRE, while formation of the Met-FISC complex was necessary and sufficient to bind to the JHRE. This binding required participation of the DNA-binding domains of both Met and FISC. The optimal DNA sequence recognized by Met and FISC contained a core consensus sequence GCACGTG. While formation of the Met-FISC complex in mosquito cells was induced by JH, heterodimerization and DNA binding of bacterially expressed Met and FISC were JH-independent, implying that additional mosquito proteins were required to modulate formation of the receptor complex.

As an important contributor to vector-borne diseases in China, in recent years, tick-borne diseases have attracted much attention because of their increasing incidence and consequent significant harm to livestock and human health. The most commonly observed human tick-borne diseases in China include Lyme borreliosis (known as Lyme disease in China), tick-borne encephalitis (known as Forest encephalitis in China), Crimean-Congo hemorrhagic fever (known as Xinjiang hemorrhagic fever in China), Q-fever, tularemia and North-Asia tick-borne spotted fever. In recent years, some emerging tick-borne diseases, such as human monocytic ehrlichiosis, human granulocytic anaplasmosis, and a novel bunyavirus infection, have been reported frequently in China. Other tick-borne diseases that are not as frequently reported in China include Colorado fever, oriental spotted fever and piroplasmosis. Detailed information regarding the history, characteristics, and current epidemic status of these human tick-borne diseases in China will be reviewed in this paper. It is clear that greater efforts in government management and research are required for the prevention, control, diagnosis, and treatment of tick-borne diseases, as well as for the control of ticks, in order to decrease the tick-borne disease burden in China.

Hormones provide generalized signals that are interpreted in a specific spatial and temporal manner by a developing or reproducing multicellular organism. The ability to respond to hormones is determined by the competence of a cell or a tissue. The ␤Ftz-F1 orphan nuclear receptor acts as a competence factor for the steroid hormone 20-hydroxyecdysone (20E) in Drosophila melanogaster metamorphosis and mosquito reproduction. The molecular nature of the ␤Ftz-F1 action remains unclear. We report that the protein-protein interaction between ␤Ftz-F1 and a p160/SRC coactivator of the ecdysone receptor, FISC, is crucial for the stage-specific expression of the 20E effector genes during mosquito reproduction. This interaction dramatically increases recruitment of FISC to the functional ecdysone receptor in a 20E-dependent manner. The presence of ␤Ftz-F1 facilitates loading of FISC and the ecdysone receptor on the target promoters, leading to enhanced local histone H4 acetylation and robust activation of the target genes. Thus, our results reveal the molecular basis of competence for the stage-specific 20E response.

The broad (br ) gene, encoding a family of C2H2 type zinc-finger DNA-binding proteins, has been shown to act as a crucial member of the 20-hydroxyecdysone (20E) regulatory hierarchy in the fruitfly, Drosophila melanogaster and the moth, Manduca sexta. In this study, we have shown that the br gene is involved in the 20E-regulatory hierarchy controlling vitellogenesis in the mosquito, Aedes aegypti. Unlike E74 and E75 early genes, expression of br was activated in previtellogenic females, during a juvenile hormone (JH)-dependent period. The levels of Z1, Z2 and Z4 isoform mRNA were elevated in the fat body of 2-day-old females after in vitro exposure to JH III. However, JH III repressed 20E activation of br in 3-to 5-day-old females, indicating a switch in hormonal commitment. Expression of Z1, Z2 and Z4 was stimulated after blood feeding in both vitellogenic tissues, the fat body and the ovary, corresponding to peaks of ecdysteroid titers. In the fat body, the mRNA profiles of these three isoforms correlated well with those of yolk protein precursor (YPP) genes. These BR isoforms were activated by 20E in fat bodies cultured in vitro and behaved as early genes, with a self-repressive autoregulatory loop that can be blocked by the protein inhibitor, cyclohexamide. Multiple binding sites for all four BR isoforms were present in the 58-regulatory region of the major YPP gene, vitellogenin (Vg). Effects of BR isoforms on the expression of Vg have been demonstrated by cell transfection analysis. In particular, BR isoforms by themselves had no effects on the Vg promoter. However, Z1 and Z4 each repressed Aedes aegypti ecdysone receptor (EcR)/Ultraspiracle (USP)-mediated 20E activation of the Vg promoter, while Z2 enhanced activation of the Vg promoter by AaEcR/AaUSP in the presence of 20E. Z3 had no obvious effect in the same experiment. These results suggested that BR isoforms are essential for proper activation and termination of the Vg gene in response to 20E. Overall, our study implicated br in the regulation of mosquito vitellogenesis.