The short day lengths of late summer program the mosquito Culex pipiens to enter a reproductive diapause characterized by an arrest in ovarian development and the sequestration of huge fat reserves. We suggest that insulin signaling and FOXO (forkhead transcription factor), a downstream molecule in the insulin signaling pathway, mediate the diapause response. When we used RNAi to knock down expression of the insulin receptor in nondiapausing mosquitoes (those reared under long day lengths) the primary follicles were arrested in a stage comparable to diapause. The mosquitoes could be rescued from this developmental arrest with an application of juvenile hormone, an endocrine trigger known to terminate diapause in this species. When dsRNA directed against FOXO was injected into mosquitoes programmed for diapause (reared under short day lengths) fat storage was dramatically reduced and the mosquito's lifespan was shortened, results suggesting that a shutdown of insulin signaling prompts activation of the downstream gene FOXO, leading to the diapause phenotype. Thus, the results are consistent with a role for insulin signaling in the short-day response that ultimately leads to a cessation of juvenile hormone production. The similarity of this response to that observed in the diapause of Drosophila melanogaster and in dauer formation of Caenorhabditis elegans suggests a conserved mechanism regulating dormancy in insects and nematodes.forkhead transcription factor ͉ insulin receptor ͉ juvenile hormone C ulex pipiens, the mosquito that vectors West Nile virus in North America, overwinters in an adult diapause (dormancy) that is programmed by the short day length of autumn (1). In response to this environmental signal, females are not attracted to their avian hosts but instead seek sources of nectar used to generate the huge fat reserves that provide the energy source for winter survival (2, 3). Although females mate in the autumn before entering protected sites for overwintering, ovarian development is halted and does not resume until the females terminate diapause in the spring and seek a blood meal.The endocrine basis for the diapause of C. pipiens, like that of other adult diapauses (4, 5), is a shutdown in the production of juvenile hormone (JH) by the corpora allata (6). This has been convincingly demonstrated by showing that an application of JH can terminate diapause in this species (6) and by the fact that removal of the corpora allata from a long-day mosquito (i.e., one not programmed for diapause) will halt reproduction and simulate a diapause-like state (7,8). Yet we know little about the signaling pathway linking the clock mechanism that perceives day length to the ultimate endocrine signal regulating JH production.This study tests the hypothesis that the insulin signaling pathway is a critical link in the regulation of mosquito diapause. Several previous studies suggest this possibility. Both the dauer state of nematodes, the dormancy equivalent of insect diapause, and the reproductive diapause of Drosophi...
piggyBac is a short inverted-repeat-type DNA transposable element originally isolated from the genome of the moth Trichoplusia ni. It is currently the gene vector of choice for the transformation of various insect species. A few sequences with similarity to piggyBac have previously been identified from organisms such as humans ( Looper), the pufferfish Takifugu rubripes ( Pigibaku), Xenopus ( Tx), Daphnia ( Pokey), and the Oriental fruit fly Bactrocera dorsalis. We have now identified 50 piggyBac-like sequences from publicly available genome sequences and expressed sequence tags (ESTs). This survey allows the first comparative examination of the distinctive piggyBac transposase, suggesting that it might contain a highly divergent DDD domain, comparable to the widespread DDE domain found in many DNA transposases and retroviral integrases which consists of two absolutely conserved aspartic acids separated by about 70 amino acids with a highly conserved glutamic acid about 35 amino acids further away. Many piggyBac-like sequences were found in the genomes of a phylogenetically diverse range of organisms including fungi, plants, insects, crustaceans, urochordates, amphibians, fishes and mammals. Also, several instances of "domestication" of the piggyBac transposase sequence by the host genome for cellular functions were identified. Novel members of the piggyBac family may be useful in genetic engineering of many organisms.
A rich chapter in the history of insect endocrinology has focused on hormonal control of diapause, especially the major roles played by juvenile hormones (JHs), ecdysteroids, and the neuropeptides that govern JH and ecdysteroid synthesis. More recently, experiments with adult diapause in Drosophila melanogaster and the mosquito Culex pipiens, and pupal diapause in the flesh fly Sarcophaga crassipalpis provide strong evidence that insulin signaling is also an important component of the regulatory pathway leading to the diapause phenotype. Insects produce many different insulin-like peptides (ILPs), and not all are involved in the diapause response; ILP-1 appears to be the one most closely linked to diapause in C. pipiens. Many steps in the pathway leading from perception of daylength (the primary environmental cue used to program diapause) to generation of the diapause phenotype remain unknown, but the role for insulin signaling in mosquito diapause appears to be upstream of JH, as evidenced by the fact that application of exogenous JH can rescue the effects of knocking down expression of ILP-1 or the Insulin Receptor. Fat accumulation, enhancement of stress tolerance, and other features of the diapause phenotype are likely linked to the insulin pathway through the action of a key transcription factor, FOXO. This review highlights many parallels for the role of insulin signaling as a regulator in insect diapause and dauer formation in the nematode Caenorhabditis elegans.
Tsetse flies are the sole vectors of human African trypanosomiasis throughout sub-Saharan Africa. Both sexes of adult tsetse feed exclusively on blood and contribute to disease transmission. Notable differences between tsetse and other disease vectors include obligate microbial symbioses, viviparous reproduction, and lactation. Here, we describe the sequence and annotation of the 366-megabase Glossina morsitans morsitans genome. Analysis of the genome and the 12,308 predicted protein–encoding genes led to multiple discoveries, including chromosomal integrations of bacterial (Wolbachia) genome sequences, a family of lactation-specific proteins, reduced complement of host pathogen recognition proteins, and reduced olfaction/chemosensory associated genes. These genome data provide a foundation for research into trypanosomiasis prevention and yield important insights with broad implications for multiple aspects of tsetse biology.
Insulin and juvenile hormone signaling direct entry of the mosquito Culex pipiens into its overwintering adult diapause, and these two critical signaling pathways appear to do so by converging on the regulation of forkhead transcription factor (FOXO). Diapause is a complex phenotype, and FOXO emerges as a prime candidate for activating many of the diverse physiological pathways that generate the diapause phenotype. Here, we used ChIP sequencing to identify direct targets of FOXO. The nearest gene in a 10-kb region surrounding a predicted binding site was extracted for each binding site, resulting in a dataset containing genes potentially regulated by FOXO. By selecting candidate genes based on their functional relevance to diapause, we identified five gene categories of potential interest, including stress tolerance, metabolic pathways, lifespan extension, cell cycle and growth regulation, and circadian rhythms. Twelve targets were prioritized for further analysis, 10 of which were validated by ChIP-quantitative PCR and quantitative real-time PCR. These 10 genes activated by FOXO are highly up-regulated during diapause and are thus strong candidates for implementation of the diapause syndrome.diapause | Culex pipiens | forkhead transcription factor | insulin D iapause is a complex phenotype characterized not only by its hallmark trait of arrested development, but also by switches in behavior, suppressed metabolism, and enhanced responses to a range of environmental insults (1, 2). In the mosquito Culex pipiens, the diapause syndrome encompasses a cessation of reproductive maturation, a switch from blood feeding to sugar feeding, migration to protective overwintering sites, suppression of metabolism, and enhanced stress responses to combat low temperature, desiccation, and pathogens (3-7). These characteristics are indeed diverse, and it is not at all clear how the major hormonal signals that govern diapause are translated into the suite of features that comprise the diapause phenotype. A shutdown in the production of juvenile hormone (JH) is a nearly universal endocrine mechanism for insect diapauses that occur in the adult stage (8), and, more recently, the insulin signaling (IS) pathway has also been implicated in diapause regulation (9-12). The JH and IS pathways merge, as shown in Fig. 1. The IS pathway is linked to stimulation of the corpora allata to produce JH, and the IS and JH signaling pathways appear to collaboratively mediate expression of the forkhead transcription factor (FOXO). In the absence of IS and JH signaling, FOXO is activated, and this activation is critical for fat accumulation (13), cessation of ovarian development (9), and the elevated antioxidant responses (14) associated with diapause in Cx. pipiens. The genetic pathway involving IS and FOXO appears to also play a critical role in regulating dauer formation in the nematode Caenorhabditis elegans (15) and reproductive diapause in the fruit fly Drosophila melanogaster (16), thus suggesting a common mechanism regulating these diverse for...
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