A standard cytogenetic photomap for the mosquito Anopheles stephensi (Diptera: Culicidae): application for physical mapping

To facilitate physical genome mapping, we have developed a new cytogenetic photomap for Anopheles stephensi (Liston) (Diptera: Culicidae), an important malaria vector in Asia. The high-resolution images of the ovarian polytene chromosomes have been straightened and divided by numbered divisions and lettered subdivisions. The exact chromosomal locations of eight DNA probes have been determined by fluorescent in situ hybridization. Using the DNA sequences, we have established correspondence between chromosomal arms among An. stephensi, Anopheles gambiae (Patton), and Anopheles funestus (Giles). The results support previous cytogenetic observations of arm translocations taking place during diversification of the species. To make the cytogenetic map useful for population genetics studies, we have indicated the chromosomal positions for the breakpoints of 19 polymorphic inversions.     

A proteogenomic analysis of Anopheles gambiae using high-resolution Fourier transform mass spectrometry

Anopheles gambiae is a major mosquito vector responsible for malaria transmission, whose genome sequence was reported in 2002. Genome annotation is a continuing effort, and many of the approximately 13,000 genes listed in VectorBase for Anopheles gambiae are predictions that have still not been validated by any other method. To identify protein-coding genes of An. gambiae based on its genomic sequence, we carried out a deep proteomic analysis using high-resolution Fourier transform mass spectrometry for both precursor and fragment ions. Based on peptide evidence, we were able to support or correct more than 6000 gene annotations including 80 novel gene structures and about 500 translational start sites. An additional validation by RT-PCR and cDNA sequencing was successfully performed for 105 selected genes. Our proteogenomic analysis led to the identification of 2682 genome search-specific peptides. Numerous cases of encoded proteins were documented in regions annotated as intergenic, introns, or untranslated regions. Using a database created to contain potential splice sites, we also identified 35 novel splice junctions. This is a first report to annotate the An. gambiae genome using high-accuracy mass spectrometry data as a complementary technology for genome annotation.     

Identification, sequence analysis, and comparative study on GSTe2 insecticide resistance gene in three main world malaria vectors: Anopheles stephensi, Anopheles culicifacies, and Anopheles fluviatilis

Glutathione S-transferases (GSTs) are soluble dimeric proteins that are involved in the metabolism, detoxification, and excretion of a large number of endogenous and exogenous compounds such as insecticides from the cell. In the current study, field specimens of Anopheles stephensi Liston, Anopheles fluviatilis James, and Anopheles culicifacies Giles collected from Sistan and Baluchistan province in Iran and subjected to World Health Organization susceptibility test. Only An. stephensi was resistant to 4% DDT. DNA extraction and rDNA-ITS2-polymerase chain reaction (PCR) for correct species identification, followed by amplification of GSTe2 gene, including exon I and II and full sequence of intron I, identified a 500-bp fragment in these three species. These fragments were purified and sequenced from both ends. The comparison of coding sequence of GSTe2 gene between these species and with Anopheles gambiae Giles showed 82 to 86% similarity at nucleic acid levels and identified nucleotide polymorphisms within An. culicifacies and An. stephensi populations. Species-specific differences have been detected in intron I of GSTe2 gene. This is in concordance with the previous studies and confirmed the conserved nature of intron sequence in GSTe2 gene of each species, probably useful as a molecular marker for species-specific identification. Phylogenetic analysis based on rDNA-ITS2, and coding (exon I and II) and noncoding sequences of GSTe2, showed the systematic relatedness between Iranian malaria vectors and the possibility of using these sequences in both differentiation of Anopheles species and defining their evolutionary relationship with the only available GSTe2 sequence of An. gambiae. These data may be useful for implementation and evaluation of malaria control programs in aspects of population genetics and molecular resistance.     

Induction of nitric oxide synthase and activation of signaling proteins in Anopheles mosquitoes by the malaria pigment, hemozoin

Anopheles stephensi, a major vector for malaria parasite transmission, responds to Plasmodium infection by synthesis of inflammatory levels of nitric oxide (NO), which can limit parasite development in the midgut. We have previously shown that Plasmodium falciparum glycosylphosphatidylinositols (PfGPIs) can induce A. stephensi NO synthase (AsNOS) expression in the midgut epithelium in vivo in a manner similar to the manner in which cytokines and NO are induced by PfGPIs in mammalian cells. In mosquito cells, signaling by PfGPIs and P. falciparum merozoites is mediated through Akt/protein kinase B (Akt/PKB), the mitogen-activated protein kinase kinase DSOR1, and extracellular signal-regulated kinase (ERK). In mammalian cells, a second parasite factor, malaria pigment or hemozoin (Hz), signals NOS induction through ERK- and nuclear factor kappa B-dependent pathways and has been demonstrated to be a novel proinflammatory ligand for Toll-like receptor 9. In this study, we demonstrate that Hz can also induce AsNOS gene expression in immortalized A. stephensi and Anopheles gambiae cell lines in vitro and in A. stephensi midgut tissue in vivo. In mosquito cells, Hz signaling is mediated through transforming growth factor beta-associated kinase 1, Akt/PKB, ERK, and atypical protein kinase C zeta/lambda. Our results show that Hz is a prominent parasite-derived signal for Anopheles and that signaling pathways activated by PfGPIs and Hz have both unique and shared components. Together with our previous findings, our data indicate that parasite signaling of innate immunity is conserved in mosquito and mammalian cells.     

Smad3 recruits the anaphase-promoting complex for ubiquitination and degradation of SnoN

Smad proteins mediate transforming growth factor-beta (TGF-beta) signaling to regulate cell growth and differentiation. SnoN is an important negative regulator of TGF-beta signaling that functions to maintain the repressed state of TGF-beta target genes in the absence of ligand. On TGF-beta stimulation, Smad3 and Smad2 translocate into the nucleus and induce a rapid degradation of SnoN, allowing activation of TGF-beta target genes. We show that Smad2- or Smad3-induced degradation of SnoN requires the ubiquitin-dependent proteasome and can be mediated by the anaphase-promoting complex (APC) and the UbcH5 family of ubiquitin-conjugating enzymes. Smad3 and to a lesser extent, Smad2, interact with both the APC and SnoN, resulting in the recruitment of the APC to SnoN and subsequent ubiquitination of SnoN in a destruction box (D box)-dependent manner. In addition to the D box, efficient ubiquitination and degradation of SnoN also requires the Smad3 binding site in SnoN as well as key lysine residues necessary for ubiquitin attachment. Mutation of either the Smad3 binding site or lysine residues results in stabilization of SnoN and in enhanced antagonism of TGF-beta signaling. Our studies elucidate an important mechanism and pathway for the degradation of SnoN and more importantly, reveal a novel role of the APC in the regulation of TGF-beta signaling.     

Smad protein and TGF-beta signaling in vascular smooth muscle cells

Transforming growth factor-beta1 (TGF-beta1) plays a role in vascular remodeling by stimulating vascular smooth muscle cell (SMC) growth and matrix-protein synthesis at sites of vascular injury. Smad proteins have been shown to mediate intracellular signaling of this growth factor. We investigated the expression and phosphorylation of Smads in cultured rat aortic smooth muscle cells. In addition, we evaluated the effects of overexpression of Smad proteins on TGF-beta signal transduction by adenovirus-mediated gene transfer. In rat SMC, Smad1, Smad2, Smad3, Smad4 and Smad5 were detected by immunoprecipitation. Using antisera against phosphorylated Smad2, we showed that TGF-beta1-induced Smad2 phosphorylation in a concentration- and time-dependent manner. Using adenovirus-mediated transfection method, we demonstrated that overexpression of Smad2 or Smad4 was associated with an increased production of TGF-beta1-induced plasminogen activator inhibitor-1 (PAI-1). However, the most prominent expression of PAI-1 was observed upon cotransfection of both Smad2 and Smad4. Both the proliferative effect of TGF-beta1 under serum-free conditions and its anti-proliferative effect under serum-rich conditions were suppressed by the adenovirus-mediated overexpression of Smad7. These results indicated that Smads proteins were expressed in vascular SMC and that they mediated TGF-beta signaling in those cells.     

AnoEST: toward A. gambiae functional genomics

Here, we present an analysis of 215,634 EST and cDNA sequences of a major vector of human malaria Anopheles gambiae structured into the AnoEST database. The expressed sequences are grouped into clusters using genomic sequence as template and associated with inferred functional annotation, including the following: corresponding Ensembl gene prediction, putative orthologous genes in other species, homology to known proteins, protein domains, associated Gene Ontology terms, and corresponding classification into broad GO-slim functional groups. AnoEST is a vital resource for interpretation of expression profiles derived using recently developed A. gambiae cDNA microarrays. Using these cDNA microarrays, we have experimentally confirmed the expression of 7961 clusters during mosquito development. Of these, 3100 are not associated with currently predicted genes. Moreover, we found that clusters with confirmed expression are nonbiased with respect to the current gene annotation or homology to known proteins. Consequently, we expect that many as yet unconfirmed clusters are likely to be actual A. gambiae genes. [AnoEST is publicly available at http://komar.embl.de, and is also accessible as a Distributed Annotation Service (DAS).].     

Mammalian transforming growth factor beta1 activated after ingestion by Anopheles stephensi modulates mosquito immunity

During the process of bloodfeeding by Anopheles stephensi, mammalian latent transforming growth factor beta1 (TGF-beta1) is ingested and activated rapidly in the mosquito midgut. Activation may involve heme and nitric oxide (NO), agents released in the midgut during blood digestion and catalysis of L-arginine oxidation by A. stephensi NO synthase (AsNOS). Active TGF-beta1 persists in the mosquito midgut to extended times postingestion and is recognized by mosquito cells as a cytokine. In a manner analogous to the regulation of vertebrate inducible NO synthase and malaria parasite (Plasmodium) infection in mammals by TGF-beta1, TGF-beta1 regulates AsNOS expression and Plasmodium development in A. stephensi. Together, these observations indicate that, through conserved immunological cross talk, mammalian and mosquito immune systems interface with each other to influence the cycle of Plasmodium development.     

Transforming growth factor beta signal transduction

Transforming growth factor beta1 (TGF-beta1) is the prototypic member of a large family of structurally related pleiotropic-secreted cytokines that play a pivotal role in the control of differentiation, proliferation, and state of activation of many different cell types including immune cells. TGF-beta family members have potent immunosuppressor activities in vitro and in vivo. These cytokines trigger their biological effects by inducing the formation of a heteromeric transmembrane serine/threonine kinase receptor complex. These receptors then initiate intracellular signaling through activation of Smad proteins, and specific Smads become phosphorylated and associate with other Smads. These heteromeric Smad complexes accumulate in the nucleus, where they modulate the expression of target genes. Recent data support the notion that Smads are important intracellular effectors of TGF-beta in immune cells. Here, we review recent advances in TGF-beta signal transduction in immune cells.     

Reduced Smad3 protein expression and altered transforming growth factor-beta1-mediated signaling in cystic fibrosis epithelial cells.

Cystic fibrosis (CF) is a disease characterized by an aggressive inflammatory response in the airways. Given the antiinflammatory properties of transforming growth factor (TGF)-beta1, it was our goal to examine components of TGF-beta1-mediated signaling in both a cultured cell model and a mouse model of CF. A CF-related reduction of protein levels of the TGF-beta1 signaling molecule Smad3 was found in both of these model systems, whereas Smad4 levels were unchanged. Functional effects of reduced Smad3 expression are manifest in our cultured cell model, as reduced basal and TGF-beta1-stimulated levels of luciferase expression using the TGF-beta1-responsive reporter construct 3TP-Lux in the CF-phenotype cells compared with control cells. However, TGF-beta1-stimulated responses using the A3-Luc reporter construct were normal in both cell lines. These results suggest that select TGF-beta1-mediated signaling pathways are impaired in CF epithelial cells. This selective loss of Smad3 protein expression in CF epithelium may also influence inflammatory responses. Our data demonstrate that both CF-phenotype cells lacking Smad3 expression, and A549 cells expressing a dominant-negative Smad3, are unable to support TGF-beta1-mediated inhibition of either the interleukin (IL)-8 or the NOS2 promoter. We conclude that a CF-related reduction in Smad3 protein expression selectively alters TGF- beta1-mediated signaling in CF epithelium, potentially contributing to aggressive inflammatory responses.     

Assessing the Drosophila melanogaster and Anopheles gambiae genome annotations using genome-wide sequence comparisons

We performed genome-wide sequence comparisons at the protein coding level between the genome sequences of Drosophila melanogaster and Anopheles gambiae. Such comparisons detect evolutionarily conserved regions (ecores) that can be used for a qualitative and quantitative evaluation of the available annotations of both genomes. They also provide novel candidate features for annotation. The percentage of ecores mapping outside annotations in the A. gambiae genome is about fourfold higher than in D. melanogaster. The A. gambiae genome assembly also contains a high proportion of duplicated ecores, possibly resulting from artefactual sequence duplications in the genome assembly. The occurrence of 4063 ecores in the D. melanogaster genome outside annotations suggests that some genes are not yet or only partially annotated. The present work illustrates the power of comparative genomics approaches towards an exhaustive and accurate establishment of gene models and gene catalogues in insect genomes.     

Mutational analysis of the Smad6 and Smad7 genes in hepatocellular carcinoma.

Resistance to the transforming growth factor-beta (TGF-beta) is a frequently found phenotype in human malignancies. The recent identification of Smad6 and Smad7, both anti-Smads which inhibit TGF-beta signaling, raises a possibility that constitutive activation of the anti-Smads by a somatic mutation may impair the TGF-beta signaling pathway. We tested this hypothesis by screening the entire coding sequences of these anti-Smads for mutations in 52 hepatocellular carcinoma (HCC) samples using polymerase chain reaction - single strand conformation polymorphism analysis. We detected no mutations, but found 3 single nucleotide polymorphisms (SNPs) in the Smad6 gene and 2 SNPs in the Smad7 gene. These results suggest that mutations of the Smad6 and Smad7 genes are not the main cause of the TGF-beta resistance in human HCC.