Mariner transposition and transformation of the yellow fever mosquito, Aedes aegypti

Sperm-mediated transformation of the honey bee, Apis mellifera

Our primary objective was to identify techniques to transform the genome of the honey bee (Apis mellifera) with foreign DNA constructs. The strategy we adopted was to linearize foreign DNA and introduce it with sperm during the instrumental insemination of virgin queen honey bees. We analysed extracts from larvae within the same cohort and isolated the predicted fragment by means of PCR amplification of genomic DNA. Larvae that carried the construct also expressed the introduced DNA. We propagated several transgenic lines for up to three generations, which demonstrates its heritability. Once carried by a queen, the construct can be detected in that queen's larvae over several months. However, there was no evidence of integration of the construct, at least as determined by genomic Southern analysis. Nevertheless, this demonstrates the general viability of the technique for introduction of DNA, and it should be augmented by further use of transposable elements that enhance integration.

The piggyBac transposon mediates germ-line transformation in the Oriental fruit fly and closely related elements exist in its genome

Germ-line transformation of a white eye strain of the Oriental fruit fly, Bactrocera dorsalis, was achieved with the piggyBac vector, derived from a transposon originally isolated from the cabbage looper moth, Trichoplusia ni. The vector was marked with the medfly white+ gene cDNA, and three transgenic lines were identified at a frequency of approximately 2% per fertile G0. Vector integrations were verified by Southern DNA hybridization, which also revealed the presence of endogenous genomic elements closely related to piggyBac. Approximately 10-20 elements per genome were evident in several B. dorsalis strains, and sequence analysis of 1.5 kb gene amplification products from two wild strains and the white eye host strain indicated 95% nucleotide and 92% amino acid sequence identity among resident elements and the T. ni element. PiggyBac was not evident by hybridization in other tephritid species, or insects previously transformed with the transposon. This is the first discovery of piggyBac beyond T. ni, and its existence in a distantly related species has important implications for the practical use of the vector and insects transformed with it.

Molecular strategies for interrupting arthropod-borne virus transmission by mosquitoes

Arthropod-borne virus (arbovirus) infections cause a number of emerging and resurgent human and veterinary infectious diseases. Traditional means of controlling arbovirus diseases include vaccination of susceptible vertebrates and mosquito control, but in many cases these have been unavailable or ineffective, and so novel strategies for disease control are needed. One possibility is genetic manipulation of mosquito vectors to render them unable to transmit arboviruses. This review describes recent work to test the concept of pathogen-derived resistance in arthropods by expression of viral genes in mosquito cell cultures and mosquitoes. Sense and antisense genome sequences from La Crosse virus (LAC) (a member of the Bunyaviridae) and dengue viruses serotypes 1 to 4 (DEN-1 to DEN-4) (members of the Flaviviridae) were expressed in mosquito cells from double-subgenomic and replicon vectors based on Sindbis virus (a member of the Togaviridae). The cells were then challenged with homologous or related viruses. For LAC, expression of antisense sequences from the small (S) genome segment, particularly full-length antisense S RNA, effectively interfered with replication of challenge virus, whereas expression of either antisense or sense RNA from the medium (M) segment was completely ineffective in LAC inhibition. Expression of sense and antisense RNA derived from certain regions of the DEN genome also blocked homologous virus replication more effectively than did RNA from other regions. Other parameters of RNA-mediated interference have been defined, such as the time when replication is blocked and the minimum size of effector RNA. The mechanism of RNA inhibition has not been determined, although it resembles double-stranded RNA interference in other nonvertebrate systems. Prospects for application of molecular strategies to control arbovirus diseases are briefly reviewed.

Purified mariner (Mos1) transposase catalyzes the integration of marked elements into the germ-line of the yellow fever mosquito, Aedes aegypti

Derivatives of the mariner transposable element, Mos1, from Drosophila mauritiana, can integrate into the germ-line of the yellow fever mosquito, Aedes aegypti. Previously, the transposase required to mobilize Mos1 was provided in trans by a helper plasmid expressing the enzyme under the control of the D. psuedoobscura heat-shock protein 82 promoter. Here we tested whether purified recombinant Mos1 transposase could increase the recovery of Ae. aegypti transformants. Mos1 transposase was injected into white-eyed, kh(w)/kh(w), Ae. aegypti embryos with a Mos1 donor plasmid containing a copy of the wild-type allele of the D. melanogaster cinnabar gene. Transformed mosquitoes were recognized by partial restoration of eye color in the G(1) animals and confirmed by Southern analyses of genomic DNA. At Mos1 transposase concentrations approaching 100 nM, the rate of germ-line transformants arising from independent insertions in G(0) animals was elevated 2-fold compared to that seen in experiments with helper plasmids. Furthermore, the recovery of total G(1) transformants was increased 7.5-fold over the frequency seen with co-injected helper plasmid. Southern blot analyses and gene amplification experiments confirmed the integration of the transposons into the mosquito genome, although not all integrations were of the expected cut-and-paste type transposition. The increased frequency of germ-line integrations obtained with purified transposase will facilitate the generation of Mos1 transgenic mosquitoes and the application of transgenic approaches to the biology of this important vector of multiple pathogens.

Expression of heterologous promoters in Lutzomyia longipalpis and Phlebotomus papatasi (Diptera: Psychodidae) cell lines

To establish a transient expression system for genes introduced into sand fly cell lines, we tested the expression of the luciferase reporter gene under control of different promoters. Towards this end, we lipofected cell lines obtained from New and Old World sand flies, LL-5 from Lutzomyia longipalpis Lutz & Neiva and PP-9 from Phlebotomus papatasi Scopoli, respectively. The relative levels of luciferase expression were studied under control of Drosophila melanogaster Meigen heat shock protein 70 (hsp70), human cytomegalovirus, simian virus 40 or Junonia coenia (Hübner) densovirus (P9) promoters. The Drosophila heat shock protein 70 promoter, originating from insect genes, functioned as a strong promoter in both cell lines. Promoters from the different virus genes also were capable of driving transgene expression in both cell lines.

Molecular strategies for interrupting arthropod-borne virus transmission by mosquitoes

Arthropod-borne virus (arbovirus) infections cause a number of emerging and resurgent human and veterinary infectious diseases. Traditional means of controlling arbovirus diseases include vaccination of susceptible vertebrates and mosquito control, but in many cases these have been unavailable or ineffective, and so novel strategies for disease control are needed. One possibility is genetic manipulation of mosquito vectors to render them unable to transmit arboviruses. This review describes recent work to test the concept of pathogen-derived resistance in arthropods by expression of viral genes in mosquito cell cultures and mosquitoes. Sense and antisense genome sequences from La Crosse virus (LAC) (a member of the Bunyaviridae) and dengue viruses serotypes 1 to 4 (DEN-1 to DEN-4) (members of the Flaviviridae) were expressed in mosquito cells from double-subgenomic and replicon vectors based on Sindbis virus (a member of the Togaviridae). The cells were then challenged with homologous or related viruses. For LAC, expression of antisense sequences from the small (S) genome segment, particularly full-length antisense S RNA, effectively interfered with replication of challenge virus, whereas expression of either antisense or sense RNA from the medium (M) segment was completely ineffective in LAC inhibition. Expression of sense and antisense RNA derived from certain regions of the DEN genome also blocked homologous virus replication more effectively than did RNA from other regions. Other parameters of RNA-mediated interference have been defined, such as the time when replication is blocked and the minimum size of effector RNA. The mechanism of RNA inhibition has not been determined, although it resembles double-stranded RNA interference in other nonvertebrate systems. Prospects for application of molecular strategies to control arbovirus diseases are briefly reviewed.

The piggyBac element is capable of precise excision and transposition in cells and embryos of the mosquito, Anopheles gambiae

The piggyBac transposable element was tested for transposition activity in plasmid-based excision and inter-plasmid transposition assays to determine if this element would function in Anopheles gambiae cells and embryos. In the Mos55 cell line, precise excision of the piggyBac element was observed only in the presence of a helper plasmid. Excision occurred at a rate of 1 event per 1000 donor plasmids screened. Precise excision of the piggyBac element was also observed in injected An. gambiae embryos, but at a lower rate of 1 excision per 5000 donor plasmids. Transposition of the marked piggyBac element into a target plasmid occurred in An. gambiae cells at a rate of 1 transposition event per 24,000 donor plasmids. The piggyBac element transposed in a precise manner, with the TTAA target site being duplicated upon insertion, in 56% of transpositions observed, and only in the presence of the piggyBac helper. The remaining transpositions resulted in a deletion of target sequence, a novel observation for the phenomenon of piggyBac element insertion. 'Hot spots' for insertion into the target plasmid were observed, with 25 of 34 events involving one particular site. These results are the first demonstration of the precise mobility of piggyBac in this malaria vector and suggest that the lepidopteran piggyBac transposon is a candidate element for germline transformation of anopheline mosquitoes.

Robust gut-specific gene expression in transgenic Aedes aegypti mosquitoes

Genetic modification of the vectorial capacity of mosquito vectors of human disease requires promoters capable of driving gene expression with appropriate tissue and stage specificity. We report on the characterization in transgenic Aedes aegypti of two mosquito gut-specific promoters. A 1.4-kb DNA fragment adjacent to the 5' end of the coding region of the Ae. aegypti carboxypeptidase (AeCP) gene and a corresponding 3.4-kb DNA fragment at the 5' end of the Anopheles gambiae carboxypeptidase (AgCP) gene were linked to a firefly luciferase reporter gene and introduced into the Ae. aegypti germ line by using Hermes and mariner (Mos1) transposons. Six independent transgenic lines were obtained with the AeCP construct and one with the AgCP construct. Luciferase mRNA and protein were abundantly expressed in the guts of transgenic mosquitoes in four of the six AeCP lines and in the AgCP line. Expression of the reporter gene was gut-specific and reached peak levels at about 24 h post-blood ingestion. The AeCP and AgCP promoters can be used to drive the expression of genes that hinder parasite development in the mosquito gut.

Two medfly promoters that have originated by recent gene duplication drive distinct sex, tissue and temporal expression patterns

Genes encoding predominantly male-specific serum polypeptides (MSSPs) in the medfly Ceratitis capitata are members of a multigene family that are structurally similar to the genes encoding odorant binding proteins of insects. To study the transcriptional regulation of the genes MSSP-alpha2 and MSSP-beta2, overlapping fragments of their promoters, containing the 5' UTRs and 5' flanking regions, were fused to the lacZ reporter gene and introduced into the medfly genome via Minos-mediated germline transformation. Transgenic flies were functionally assayed for beta-galactosidase activity. Despite their extensive sequence similarity, the two gene promoters show distinct expression patterns of the reporter gene, consistent with previously reported evidence for analogous transcriptional activity of the corresponding endogenous genes. The MSSP-alpha2 promoter drives gene expression specifically in the fat body of the adult males, whereas the MSSP-beta2 promoter directs gene expression in the midgut of both sexes. In contrast, similar transformation experiments in Drosophila melanogaster showed that both promoters drive the expression of the reporter gene in the midgut of adult flies of both sexes. Thus, the very same MSSP-alpha2 promoter fragment directs expression in the adult male fat body in Ceratitis, but in the midgut of both sexes in Drosophila. Our data suggest that through the evolution of the MSSP gene family a limited number of mutations that occurred within certain cis-acting elements, in combination with new medfly-specific trans-acting factors, endowed these recently duplicated genes with distinct sex-, tissue-, and temporal-specific expression patterns.

Distribution of the transposable element mariner in anopheline mosquitoes

We have surveyed the distribution of the transposable element mariner using PCR in 23 species of Anopheles mosquitoes, including all of the most important vectors of malaria in South-east Asia. Sequencing of the nine positive species revealed elements from the irritans, mauritiana and mellifera subfamilies. These are the first data showing the presence of three subfamilies of mariners in anophelines. The elements we encountered are likely to be inactive, based on the presence of multiple stop codons and/or frameshifts.

In vivo transposon mutagenesis of the methanogenic archaeon Methanosarcina acetivorans C2A using a modified version of the insect mariner-family transposable element Himar1

We present here a method for in vivo transposon mutagenesis of a methanogenic archaeon, Methanosarcina acetivorans C2A, which because of its independence from host-specific factors may have broad application among many microorganisms. Because there are no known Methanosarcina transposons we modified the mariner transposable element Himar1, originally found in the insect Hematobia irritans, to allow its use in this organism. This element was chosen because, like other mariner elements, its transposition is independent of host factors, requiring only its cognate transposase. Modified mini-Himar1 elements were constructed that carry selectable markers that are functional in Methanosarcina species and that express the Himar1 transposase from known Methanosarcina promoters. These mini-mariner elements transpose at high frequency in M. acetivorans to random sites in the genome. The presence of an Escherichia coli selectable marker and plasmid origin of replication within the mini-mariner elements allows facile cloning of these transposon insertions to identify the mutated gene. In preliminary experiments, we have isolated numerous mini-mariner-induced M. acetivorans mutants, including ones with insertions that confer resistance to toxic analogs and in genes that encode proteins involved in heat shock, nitrogen fixation, and cell-wall structures.

Promoter sequences of the putative Anopheles gambiae apyrase confer salivary gland expression in Drosophila melanogaster

The saliva of blood-feeding arthropods contains an apyrase that facilitates hematophagy by inhibiting the ADP-induced aggregation of the host platelets. We report here the isolation of a salivary gland-specific cDNA encoding a secreted protein that likely represents the Anopheles gambiae apyrase. We describe also two additional members of the apyrase/5'-nucleotidase family. The cDNA corresponding to the AgApyL1 gene encodes a secreted protein that is closely related in sequence to the apyrase of the yellow fever mosquito, Aedes aegypti, and whose expression appears enriched in, but not restricted to, female salivary glands. The AgApyL2 gene was found searching an A. gambiae data base, and its expression is restricted to larval stages. We isolated the gene encoding the presumed A. gambiae apyrase (AgApy) and we tested its putative promoter for the tissue-specific expression of the LacZ gene from Escherichia coli in transgenic Drosophila melanogaster. All the transgenic lines analyzed showed a weak but unambiguous staining of the adult glands, indicating that some of the salivary gland-specific transcriptional regulatory elements are conserved between the malaria mosquito and the fruit fly. The availability of salivary gland-specific promoters may be useful both for studies on vector-parasite interactions and, potentially, for the targeted tissue-specific expression of anti-parasite genes in the mosquito.

Engineering blood meal-activated systemic immunity in the yellow fever mosquito, Aedes aegypti

Progress in molecular genetics makes possible the development of alternative disease control strategies that target the competence of mosquitoes to transmit pathogens. We tested the regulatory region of the vitellogenin (Vg) gene of Aedes aegypti for its ability to express potential antipathogen factors in transgenic mosquitoes. Hermes-mediated transformation was used to integrate a 2.1-kb Vg-promoter fragment driving the expression of the Defensin A (DefA) coding region, one of the major insect immune factors. PCR amplification of genomic DNA and Southern blot analyses, carried out through the ninth generation, showed that the Vg-DefA transgene insertion was stable. The Vg-DefA transgene was strongly activated in the fat body by a blood meal. The mRNA levels reached a maximum at 24-h postblood meal, corresponding to the peak expression time of the endogenous Vg gene. High levels of transgenic defensin were accumulated in the hemolymph of bloodfed female mosquitoes, persisting for 20-22 days after a single blood feeding. Purified transgenic defensin showed antibacterial activity comparable to that of defensin isolated from bacterially challenged control mosquitoes. Thus, we have been able to engineer the genetically stable transgenic mosquito with an element of systemic immunity, which is activated through the blood meal-triggered cascade rather than by infection. This work represents a significant step toward the development of molecular genetic approaches to the control of vector competence in pathogen transmission.

A repressible female-specific lethal genetic system for making transgenic insect strains suitable for a sterile-release program

We have developed a tetracycline-repressible female-specific lethal genetic system in the vinegar fly Drosophila melanogaster. One component of the system is the tetracycline-controlled transactivator gene under the control of the fat body and female-specific transcription enhancer from the yolk protein 1 gene. The other component consists of the proapoptotic gene hid under the control of a tetracycline-responsive element. Males and females of a strain carrying both components are viable on medium supplemented with tetracycline, but only males survive on normal medium. A strain with such properties would be ideal for a sterile-insect release program, which is most effective when only males are released in the field.

Stable germline transformation of the malaria mosquito Anopheles stephensi

Anopheline mosquito species are obligatory vectors for human malaria, an infectious disease that affects hundreds of millions of people living in tropical and subtropical countries. The lack of a suitable gene transfer technology for these mosquitoes has hampered the molecular genetic analysis of their physiology, including the molecular interactions between the vector and the malaria parasite. Here we show that a transposon, based on the Minos element and bearing exogenous DNA, can integrate efficiently and stably into the germ line of the human malaria vector Anopheles stephensi, through a transposase-mediated process.

Blood-feeding in mosquitoes: probing time and salivary gland anti-haemostatic activities in representatives of three genera (Aedes, Anopheles, Culex)

Mosquitoes (Diptera: Culicidae) face their hosts' haemostatic mechanisms when attempting to feed on blood. Accordingly, they antagonize haemostasis by salivary agents that include anti-clotting, anti-platelet and vasodilatory compounds. Because haemostasis is a complex and redundant physiological response that varies between vertebrates, it is to be expected that haematophagous animals have a salivary armoury that most efficiently counteracts their preferred hosts. The mosquito Culex quinquefasciatus Say, which has a strong tendency to ornithophagy, appears to have only recently adapted to mammals and may not have evolved efficient mechanisms to counteract mammalian platelet responses, while birds only have relatively inefficient thrombocytes. Accordingly, we compared the probing behaviour of Cx. quinquefasciatus with two other mosquito species from different backgrounds: Aedes aegypti (L.) and Anopheles albimanus Weidemann, that have apparently had a longer evolutionary association with mammals. Culex takes much more time to find blood on a mammalian host (human or mouse) when compared to the two other mosquito species, but does not differ in probing behaviour when feeding on a chicken. Salivary anti-haemostatic components were also measured in those three species of mosquito and results are discussed in context with the probing behaviour.

Germ-line transformation of pink bollworm (Lepidoptera: gelechiidae) mediated by the piggyBac transposable element

The pink bollworm, Pectinophora gossypiella, is a world-wide pest of cultivated cotton. In certain growing regions populations are suppressed by a sterile release strategy. Efforts to improve the sterile insect technique as well as our understanding of lepidopteran biology could benefit greatly from a germ-line transformation system. We report transformation of pink bollworm with a piggyBac transposable element carrying the enhanced green flourescent protein (EGFP) marker gene. This vector-marker system resulted in recovery of transgenics at a rate of approximately 3.5%. Integration of the transforming construct that was typical of piggyBac was demonstrated by Southern analysis and sequence determination of transposon flanks. Expression of the EGFP marker was visualized by fluorescent microscopy and Western Blot analysis. Maintenance of transformed strains indicates that the transgene segregates in a Mendelian fashion and has been stable over fourteen generations to date.

Mosquito immune responses and malaria transmission: lessons from insect model systems and implications for vertebrate innate immunity and vaccine development

The introduction of novel biochemical, genetic, molecular and cell biology tools to the study of insect immunity has generated an information explosion in recent years. Due to the biodiversity of insects, complementary model systems have been developed. The conceptual framework built based on these systems is used to discuss our current understanding of mosquito immune responses and their implications for malaria transmission. The areas of insect and vertebrate innate immunity are merging as new information confirms the remarkable extent of the evolutionary conservation, at a molecular level, in the signaling pathways mediating these responses in such distant species. Our current understanding of the molecular language that allows the vertebrate innate immune system to identify parasites, such as malaria, and direct the acquired immune system to mount a protective immune response is very limited. Insect vectors of parasitic diseases, such as mosquitoes, could represent excellent models to understand the molecular responses of epithelial cells to parasite invasion. This information could broaden our understanding of vertebrate responses to parasitic infection and could have extensive implications for anti-malarial vaccine development.

Extrachromosomal transposition of the transposable element Minos occurs in embryos of the silkworm Bombyx mori

To assess the ability of the transposable element Minos to act as a vector for genetic manipulation of the silkworm Bombyx mori, an extrachromosomal transposition assay based on three plasmids was performed. The three plasmids - helper, donor and target - were co-injected into preblastoderm embryos. Low molecular weight DNA was extracted from the embryos at the stage of blastokinesis and used to transform Escherichia coli. High frequency of transposition was observed in the presence of a helper plasmid possessing an intronless Minos transposase gene, whereas transposition did not occur in the presence of a helper plasmid with the intron-bearing transposase gene. Sequence analysis of the insertion sites showed that Minos always inserts into a TA dinucleotide. Although the insertions are distributed throughout the target gene, there was a preference for certain insertion sites. However, no consensus could be identified in the sequence flanking the target site. The results strongly suggest that the transposable element Minos has the potential to be used as a vector in the silkworm and probably in other lepidopteran insects.

Mobility assays confirm the broad host-range activity of the Minos transposable element and validate new transformation tools

Fast and reliable methods for assessing the mobility of the transposable element Minos have been developed. These methods are based on the detection of excision and insertion of Minos transposons from and into plasmids which are co-introduced into cells. Excision is detected by polymerase chain reaction (PCR) with appropriate primers. Transposition is assayed by marker rescue in Escherichia coli, using a transposon plasmid that carries a tetracycline resistance gene and a target plasmid carrying a gene that can be selected against in E. coli. Using both assays, Minos was shown to transpose in Drosophila melanogaster cells and embryos, and in cultured cells of a mosquito, Aedes aegypti, and a lepidopteran, Spodoptera frugiperda. In all cases, mobility was dependent on the presence of exogenously supplied transposase, and both excision and transposition were precise. The results indicate that Minos can transpose in heterologous insect species with comparable efficiencies and therefore has the potential to be used as a transgenesis vector for diverse species.

Somatic integration and long-term transgene expression in normal and haemophilic mice using a DNA transposon system

The development of non-viral gene-transfer technologies that can support stable chromosomal integration and persistent gene expression in vivo is desirable. Here we describe the successful use of transposon technology for the nonhomologous insertion of foreign genes into the genomes of adult mammals using naked DNA. We show that the Sleeping Beauty transposase can efficiently insert transposon DNA into the mouse genome in approximately 5-6% of transfected mouse liver cells. Chromosomal transposition resulted in long-term expression (>5 months) of human blood coagulation factor IX at levels that were therapeutic in a mouse model of haemophilia B. Our results establish DNA-mediated transposition as a new genetic tool for mammals, and provide new strategies to improve existing non-viral and viral vectors for human gene therapy applications.

Chitinases of the avian malaria parasite Plasmodium gallinaceum, a class of enzymes necessary for parasite invasion of the mosquito midgut

The Plasmodium ookinete produces chitinolytic activity that allows the parasite to penetrate the chitin-containing peritrophic matrix surrounding the blood meal in the mosquito midgut. Since the peritrophic matrix is a physical barrier that the parasite must cross to invade the mosquito, and the presence of allosamidin, a chitinase inhibitor, in a blood meal prevents the parasite from invading the midgut epithelium, chitinases (3.2.1.14) are potential targets of malaria parasite transmission-blocking interventions. We have purified a chitinase of the avian malaria parasite Plasmodium gallinaceum and cloned the gene, PgCHT1, encoding it. PgCHT1 encodes catalytic and substrate-binding sites characteristic of family 18 glycohydrolases. Expressed in Escherichia coli strain AD494 (DE3), recombinant PgCHT1 was found to hydrolyze polymeric chitin, native chitin oligosaccharides, and 4-methylumbelliferone derivatives of chitin oligosaccharides. Allosamidin inhibited recombinant PgCHT1 with an IC(50) of 7 microM and differentially inhibited two chromatographically separable P. gallinaceum ookinete-produced chitinase activities with IC(50) values of 7 and 12 microM, respectively. These two chitinase activities also had different pH activity profiles. These data suggest that the P. gallinaceum ookinete uses products of more than one chitinase gene to initiate mosquito midgut invasion.

Chemical and gamma-ray mutagenesis of the white gene in Aedes aegypti

A molecular understanding of an insect gene can be facilitated by analysing the phenotypes of mutants for that gene. Protocols were developed for both chemical and gamma-ray mutagenesis in Aedes aegypti using the white (w) gene as an assay. Wild-type adult males were subjected to varying doses of either ethyl methanesulphonate (0. 1%, 0.5% or 1%) or gamma rays (1500 R or 3000 R), mated to females homozygous for the recessive w mutation, and progeny screened for the w phenotype, indicating non-complementation. The expression of newly induced w alleles was either complete or mosaic. Gamma-ray mutagenesis resulted in high (1.65 or 6.39%, depending on dose) induction of mutant alleles for the w gene, but not for a different gene, red-eye (0.15%). Gamma-ray-induced w alleles did not revert at a reasonable frequency following additional irradiation, suggesting that the high rate of gamma-ray-induced w mutagenesis is not due to a transposon insertion event.

Mariner (Mos1) transposase and genomic integration of foreign gene sequences in Bombyx mori cells

Widespread occurrence in insects and the capacity to transpose in the absence of host-derived factors means that mariner-like elements are considered to be attractive candidates for the development of a universal insect genetic transformation system. Here we show that the Mos1 mariner element of Drosophila mauritiana is capable of mediating excision and transposition events in a silkmoth (Bombyx mori) derived tissue culture cell line (Bm5 cells). Plasmid rescue assays, in combination with Southern hybridization and polymerase chain reaction (PCR) analyses, confirm that the Mos1 transposase can mediate excision of DNA sequences, inserted between terminally repeated sequences recognized by the transposase, and integration into the chromosomal DNA of the Bm5 cells. In addition to chromosomal integration events, inter- and intraplasmid transposition and target element excision events were also detected. Approximately 50% of the plasmids recovered from plasmid rescue assays were found to contain the 'signature' of Mos1-specific excision and/or integration events, indicating that the mariner transposase functions efficiently in the Bombyx cells. Because mariner-induced excision and integration events are strictly dependent on the presence of a co-transfected Mos1 transposase expression vector, it is clear that the multiple copies of endogenous mariner-like elements (Bmmar1) that exist in the Bombyx genome are neither functional nor do they interfere with the efficiency of the transposition process. Thus, the Mos1 element and, probably, mariner elements, in general, hold great promise for the development of genetic transformation systems for lepidopteran insects.

Genetics of mosquito vector competence

Mosquito-borne diseases are responsible for significant human morbidity and mortality throughout the world. Efforts to control mosquito-borne diseases have been impeded, in part, by the development of drug-resistant parasites, insecticide-resistant mosquitoes, and environmental concerns over the application of insecticides. Therefore, there is a need to develop novel disease control strategies that can complement or replace existing control methods. One such strategy is to generate pathogen-resistant mosquitoes from those that are susceptible. To this end, efforts have focused on isolating and characterizing genes that influence mosquito vector competence. It has been known for over 70 years that there is a genetic basis for the susceptibility of mosquitoes to parasites, but until the advent of powerful molecular biological tools and protocols, it was difficult to assess the interactions of pathogens with their host tissues within the mosquito at a molecular level. Moreover, it has been only recently that the molecular mechanisms responsible for pathogen destruction, such as melanotic encapsulation and immune peptide production, have been investigated. The molecular characterization of genes that influence vector competence is becoming routine, and with the development of the Sindbis virus transducing system, potential antipathogen genes now can be introduced into the mosquito and their effect on parasite development can be assessed in vivo. With the recent successes in the field of mosquito germ line transformation, it seems likely that the generation of a pathogen-resistant mosquito population from a susceptible population soon will become a reality.

Toward Anopheles transformation: Minos element activity in anopheline cells and embryos

The ability of the Minos transposable element to function as a transformation vector in anopheline mosquitoes was assessed. Two recently established Anopheles gambiae cell lines were stably transformed by using marked Minos transposons in the presence of a helper plasmid expressing transposase. The markers were either the green fluorescent protein or the hygromycin B phosphotransferase gene driven by the Drosophila Hsp70 promoter. Cloning and sequencing of the integration sites demonstrated that insertions in the cell genome occurred through the action of Minos transposase. Furthermore, an interplasmid transposition assay established that Minos transposase is active in the cytoplasmic environment of Anopheles stephensi embryos: interplasmid transposition events isolated from injected preblastoderm embryos were identified as Minos transposase-mediated integrations, and no events were recorded in the absence of an active transposase. These results demonstrate that Minos vectors are suitable candidates for germ-line transformation of anopheline mosquitoes.

Development of a Sindbis virus expression system that efficiently expresses green fluorescent protein in midguts of Aedes aegypti following per os infection

A double subgenomic Sindbis (dsSIN) virus, MRE/3'2 J/GFP, was constructed to efficiently express green fluorescent protein (GFP) in the midgut of Aedes aegypti following per os infection. The MRE/3'2 J/GFP RNA genome contained the nonstructural genes and cis-acting sequences of the dsSIN virus, TE/3'2 J/GFP, but had the structural genes of MRE16 SIN virus. MRE/3'2 J/GFP virus, unlike TE/3'2 J/GFP virus, efficiently infected mosquitoes orally. At 1-2 days postinfection, GFP was observed as multiple foci of expression on the lumenal side of the midgut. At 10-12 days postinfection, thirteen of fifteen mosquitoes infected with MRE/3'2 J/GFP virus had high levels of GFP expression in the mosquito midgut. The MRE3'2 J dsSIN expression system should be an important tool for efficient gene expression in Ae. aegypti midguts.

Two-dimensional gel analysis of haemolymph proteins from Plasmodium-melanizing and -non-melanizing strains of Anopheles gambiae

Haemolymph polypeptides from Plasmodium-refractory and -susceptible mosquitoes were compared by one- and two-dimensional gel electrophoresis. The refractory strain of Anopheles gambiae kills malaria parasites by a humoral melanization mechanism whereas the parasites develop normally in susceptible mosquitoes. The two strains respond in a similar manner to carboxy-methyl-Sephadex beads that have been injected into the thoracic haemocoel, i.e. beads are strongly melanized in refractory but not susceptible mosquitoes. Protein profiles were compared between strains following cold shock (naïve control), saline injection and Sephadex bead injection. Using the susceptible naïve control as the standard, eight constitutively expressed polypeptides were specific to naïve susceptible mosquitoes while twelve other spots were reduced, enhanced or specific to refractory mosquitoes. Several of the strain-specific spots probably comprise related pairs (one in each strain) which vary only in isoelectric focusing point. Nine spots were induced by sham injection or by an injection of beads or saline, but none was reproducibly different between the strains. Amino acid sequence analysis of one of the refractory strain-specific spots identified it as AgSp14D1, an A. gambiae infection-responsive serine protease that is most similar to the Drosophila gene easter and Manduca prophenoloxidase activating enzyme. This gene maps to polytene chromosome division 14, which has been implicated in the melanization phenotype by quantitative trait loci mapping.

Structure of hermes integrations in the germline of the yellow fever mosquito, Aedes aegypti

The Hermes transposable element is derived from the house fly, Musca domestica, and can incorporate into the germline of the yellow fever mosquito, Aedes aegypti. Preliminary Southern analyses indicated that Hermes integrated along with the marker gene into the mosquito genomic DNA. Here we show that Hermes integrations are accompanied by the integration of the donor plasmid as well. In addition, breaks in the donor plasmid DNAs do not occur precisely, or at the end of the terminal inverted repeats, and are accompanied by small deletions in the plasmids. Furthermore, integrations do not cause the typical 8-bp duplications of the target site DNA. No integrations are observed in the absence of a source of Hermes transposase. The Hermes transposase clearly did not catalyse precise cut-and-paste transposition in these transformed lines. It may have integrated the transposon through general recombination or through a partial replicative transposition mechanism. The imprecision of Hermes integration may result from interactions of the transposase with an endogenous hAT-like element in the mosquito genome.

Characterization of a carboxypeptidase A gene from the mosquito, Aedes aegypti

A gut-specific carboxypeptidase A gene (AeCPA) from the mosquito, Aedes aegypti, was cloned and characterized. The gene has an open reading frame that predicts a protein of 427 amino acids, 61% of which are identical to an Anopheles gambiae carboxypeptidase A sequence. AeCPA messenger RNA (mRNA) was not detected during larval and pupal development. In situ hybridization experiments indicated that AeCPA mRNA is expressed by posterior midgut epithelial cells. In sharp contrast to An. gambiae carboxypeptidase A gene expression, AeCPA mRNA accumulates to high levels only late ( approximately 16-24 h) after ingestion of a blood meal. The temporal profile of AeCPA gene induction is similar to that of Ae. aegypti late trypsin, suggesting the existence of common regulatory elements.

cis and trans factors affecting Mos1 mariner evolution and transposition in vitro, and its potential for functional genomics

Mos1 and other mariner / Tc1 transposons move horizon-tally during evolution, and when transplanted into heterologous species can transpose in organisms ranging from prokaryotes to protozoans and vertebrates. To further develop the Drosophila Mos1 mariner system as a genetic tool and to probe mechanisms affecting the regulation of transposition activity, we developed an in vitro system for Mos1 transposition using purified transposase and selectable Mos1 derivatives. Transposition frequencies of nearly 10(-3)/target DNA molecule were obtained, and insertions occurred at TA dinucleotides with little other sequence specificity. Mos1 elements containing only the 28 bp terminal inverted repeats were inactive in vitro, while elements containing a few additional internal bases were fully active, establishing the minimal cis -acting requirements for transposition. With increasing transposase the transposition frequency increased to a plateau value, in contrast to the predictions of the protein over-expression inhibition model and to that found recently with a reconstructed Himar1 transposase. This difference between the 'natural' Mos1 and 'reconstructed' Himar1 transposases suggests an evolutionary path for down-regulation of mariner transposition following its introduction into a naïve population. The establishment of the cis and trans requirements for optimal mariner transposition in vitro provides key data for the creation of vectors for in vitro mutagenesis, and will facilitate the development of in vivo systems for mariner transposition.

Green fluorescent protein as a genetic marker in transgenic Aedes aegypti

We report here the use of the enhanced green fluorescent protein (EGFP) from the jellyfish, Aequorea victoria, as a genetic marker for the genetic transformation of mosquitoes. The EGFP gene, under the control of the actin5C promoter of Drosophila melanogaster was inserted into the Hermes transposable element. Preblastoderm embryos of a wild-type strain of the yellow fever mosquito, Aedes aegypti, were microinjected with this plasmid, together with a helper plasmid containing the Hermes transposase placed under the control of the D. melanogaster hsp70 promoter. Somatic EGFP expression was observed during early instars in approximately one-half of all G0 individuals. Two G1 individuals arising from a G0 female displayed high levels of EGFP gene expression during all stages of development. EGFP was transmitted in a Mendelian fashion to the G2 and G3 generations and molecular analysis confirmed the presence of the Hermes[actin5C:EGFP] gene in these insects. These results clearly demonstrate that EGFP can be used as an effective genetic marker in wild-type Ae. aegypti and most likely in other mosquito species as well.

Germline transformation of the silkworm Bombyx mori L. using a piggyBac transposon-derived vector

We have developed a system for stable germline transformation in the silkworm Bombyx mori L. using piggyBac, a transposon discovered in the lepidopteran Trichoplusia ni. The transformation constructs consist of the piggyBac inverted terminal repeats flanking a fusion of the B. mori cytoplasmic actin gene BmA3 promoter and the green fluorescent protein (GFP). A nonautonomous helper plasmid encodes the piggyBac transposase. The reporter gene construct was coinjected into preblastoderm eggs of two strains of B. mori. Approximately 2% of the individuals in the G1 broods expressed GFP. DNA analyses of GFP-positive G1 silkworms revealed that multiple independent insertions occurred frequently. The transgene was stably transferred to the next generation through normal Mendelian inheritance. The presence of the inverted terminal repeats of piggyBac and the characteristic TTAA sequence at the borders of all the analyzed inserts confirmed that transformation resulted from precise transposition events. This efficient method of stable gene transfer in a lepidopteran insect opens the way for promising basic research and biotechnological applications.

The chitinase PfCHT1 from the human malaria parasite Plasmodium falciparum lacks proenzyme and chitin-binding domains and displays unique substrate preferences

Within hours after the ingestion of a blood meal, the mosquito midgut epithelium synthesizes a chitinous sac, the peritrophic matrix. Plasmodium ookinetes traverse the peritrophic matrix while escaping the mosquito midgut. Chitinases (EC 3.2.1.14) are critical for parasite invasion of the midgut: the presence of the chitinase inhibitor, allosamidin, in an infectious blood meal prevents oocyst development. A chitinase gene, PgCHT1, recently has been identified in the avian malaria parasite P. gallinaceum. We used the sequence of PgCHT1 to identify a P. falciparum chitinase gene, PfCHT1, in the P. falciparum genome database. PfCHT1 differs from PgCHT1 in that the P. falciparum gene lacks proenzyme and chitin-binding domains. PfCHT1 was expressed as an active recombinant enzyme in Escherichia coli. PfCHT1 shares with PgCHT1 a substrate preference unique to Plasmodium chitinases: the enzymes cleave tri- and tetramers of GlcNAc from penta- and hexameric oligomers and are unable to cleave smaller native chitin oligosaccharides. The pH activity profile of PfCHT1 and its IC(50) (40 nM) to allosamidin are distinct from endochitinase activities secreted by P. gallinaceum ookinetes. Homology modeling predicts that PgCHT1 has a novel pocket in the catalytic active site that PfCHT1 lacks, which may explain the differential sensitivity of PfCHT1 and PgCHT1 to allosamidin. PfCHT1 may be the ortholog of a second, as yet unidentified, chitinase gene of P. gallinaceum. These results may allow us to develop novel strategies of blocking human malaria transmission based on interfering with P. falciparum chitinase.

The Queensland fruit fly, Bactrocera tryoni, contains multiple members of the hAT family of transposable elements

Members of the hAT transposable element family are mobile in non-host insect species and have been used as transformation vectors in some of these species. We report that the Queensland fruit fly, Bactrocera tryoni, contains at least two types of insect hAT elements called Homer and a Homer-like element (HLE). The Homer element is 3789 bp in size and contains 12-bp imperfect inverted terminal repeats. The Homer element contains a long open reading frame (ORF) that encodes a putative transposase. Three different copies of this long ORF were recovered from the B. tryoni genome and, upon transcription and translation in an in vitro system, all produced transposase. The HLE is an incomplete element since no 3' inverted terminal repeat (ITR) was found. Homer and the HLE are as related to one another as either is to the other insect hAT elements such as Hermes, hobo, hermit and hopper. The structure and distribution of these two Homer elements is described.

A P element-homologous sequence in the house fly, Musca domestica

Sequences homologous to the P transposable element have been identified in Musca domestica. Sequence analysis of a genomic clone (Md-P1) indicates that, although the house fly P element has lost its coding capacity, the basic general structure of drosophilid P elements is present. The house fly P element sequence shares a number of structural features with that from the blow fly, Lucilia cuprina, including a large intron separating exons 1 and 2, two additional introns interrupting exon 2 and the apparent absence of inverted repeat termini. Within a relatively well-conserved central region, the house fly sequence shows 59% similarity to the D. melanogaster P element, but distal regions are more diverged. Southern blot analysis of several strains indicated the presence of at least four P element copies.

Germline transformation of Drosophila melanogaster with the piggyBac transposon vector

Germline transformation of Drosophila melanogaster was attempted with the piggyBac gene-transfer system from the cabbage looper moth, Trichoplusia ni. Using a self-regulated transposase helper and a white marked vector, a transformation frequency of 1-3% per fertile G0 was obtained, similar to that previously achieved in the medfly. Use of an hsp70-regulated helper increased this frequency more than eight-fold. Transformation with a vector marked with white and green fluorescent protein (GFP) under polyubiquitin-nuclear localizing sequence regulation yielded seventy G1 transformants which all expressed GFP, but only twenty-seven of these expressed eye pigmentation that would have allowed their selection based on white+ expression. PiggyBac transformation in two distantly related dipteran species and efficient expression of the gfp marker supports the potential use of this system in other dipterans, and perhaps insects in general.

Anopheles albitarsis eggs: ultrastructural analysis of chorion layers after permeabilization

Construction of transgenic Anopheles mosquitoes refractory to Plasmodium requires knowledge of mosquito developmental biology. In order to study Anopheles embryology the removal or, alternatively, the permeabilization of the melanized and sclerotized egg chorion were attempted. The protocol classically used for chorion removal of Drosophila eggs was applied, with partial efficacy, to Anopheles albitarsis, a neotropical malaria vector. Each step was monitored by scanning electron microscopy and the results suggest differences in chorion composition between the two taxa. As an alternative to chorion removal, mosquito eggs were permeabilized with benserazide, an inhibitor of Dopa Decarboxylase, one of the enzymes needed for mosquito eggshell sclerotization. Embryo morphology and viability were not affected by this treatment. Permeabilization of the egg chorion allowed the ultrastructural observation of an internal homogeneous endochorion and an external compound exochorion, the latter consisting of a basal lamellar layer and protruding tubercles.

Dengue vector surveillance and control

This review describes efforts being undertaken to develop new tools and strategies to monitor and control dengue fever mosquitoes, mainly Aedes aegypti. With the growing realization that the magnitude of the global dengue/dengue haemorrhagic fever problem rivals that of malaria and infectious diseases such as hepatitis, and that old strategies are unsuitable in today's world, this problem requires urgent attention. The new tactics involve proper targeting of important breeding sites and diverse control methodologies ranging from biological control to molecular transformation of the vectors themselves.

Hyperactive transposase mutants of the Himar1 mariner transposon

Mariner-family transposable elements are active in a wide variety of organisms and are becoming increasingly important genetic tools in species lacking sophisticated genetics. The Himar1 element, isolated from the horn fly, Haematobia irritans, is active in Escherichia coli when expressed appropriately. We used this fact to devise a genetic screen for hyperactive mutants of Himar1 transposase that enhance overall transposition from approximately 4- to 50-fold as measured in an E. coli assay. Purified mutant transposases retain their hyperactivity, although to a lesser degree, in an in vitro transposition assay. Mutants like those described herein should enable sophisticated analysis of the biochemistry of mariner transposition and should improve the use of these elements as genetic tools, both in vivo and in vitro.

Resident aliens: the Tc1/mariner superfamily of transposable elements

Transgenic technology is currently applied to several animal species of agricultural or medical importance, such as fish, cattle, mosquitos and parasitic worms. However, the repertoire of genetic tools used for molecular analyses of mice and Drosophila is not always applicable to other species. For example, while retroviral enhancer-trap experiments in mice can be based on embryonic stem (ES) cell technology, this is not currently an option with other animals. Similarly, the germline transformation of Drosophila depends on the use of the P-element transposon, which does not jump in other genera. This article analyses the main characteristics of Tc1/mariner transposable elements, examines some of the factors that have contributed to their evolutionary success, and describes their potential, as well as their limitations, for transgenesis and insertional mutagenesis in diverse animals.

Expression of a functional antibody fragment in the gut of Rhodnius prolixus via transgenic bacterial symbiont Rhodococcus rhodnii

Expression within insects of foreign antiparasitic gene products via microbial symbionts could be used to prevent transmission of vector-borne pathogens to vertebrate hosts. Genetically transformed symbiotic bacteria Rhodococcus rhodnii expressed functional antibody fragments (rDB3 encoding murine V(H)/K which binds progesterone) that were exported into the gut lumen of the triatomine bug Rhodnius prolixus (Hemiptera: Reduviidae), a vector of Chagas disease. Transgenic symbionts were maintained in successive nymphal instars and adults of Rhodnius prolixus despite competition with native untransformed Rhodococcus rhodnii. This is the first description of a functional mammalian antibody fragment expressed in an insect. Our system is a model for constructing paratransgenic insects (insects carrying transformed symbionts) with compromised ability to transmit pathogens.

Construction of modular and versatile plasmid vectors for the high-level expression of single or multiple genes in insects and insect cell lines

We have constructed a series of plasmid vectors for the expression of foreign genes in insects or insect cell lines. We incorporated the Drosophila hsp70 and actin 5C promoters, as well as the hr5 enhancer-driven baculovirus ie1 promoter, into plasmids that allow convenient cloning of heterologous genes into multiple cloning sites. We combined these promoters with either a short, double poly-adenylation site derived from the Heliothis virescens p63 chaperonin gene, or with a fusion of the small t intron with the early 3' untranslated region and poly-adenylation sites of SV40. Unique eight base cutter restriction sites flanking the promoters and poly-adenylation sequences make it possible to transfer the entire transcription units into other sequence contexts, for example, into transposable elements or into other plasmids bearing selectable marker genes. It is also convenient to combine two of our transcription units on the same plasmid in order to express multiple genes simultaneously. To test the ability of our vectors to drive expression of reporter genes, luciferase derivatives were made of the expression plasmids and introduced into Aedes albopictus C6/36 cells by electroporation or into Anopheles gambiae embryos by biolistic particle bombardment. All three promoters directed high levels of luciferase expression. However, there were differences in their relative activities in the two experimental systems. In C6/36 cells, the actin 5C and hr5-ie1 promoters were significantly more active than the hsp70 promoter. In Anopheles embryos, hsp70 and actin 5C had maximal activities, while hr5-ie1 was weaker. We also found that the constructs containing the SV40 small t intron and early 3' untranslated region sequences had higher expression levels than their counterparts containing the Heliothis poly-adenylation sequence. Our most active construct combines the actin 5C promoter with the SV40 intron and 3' untranslated region sequences. This vector was also used to drive expression of a visible marker, the enhanced green fluorescent protein gene, resulting in readily visible green fluorescent protein expression in C6/36 cells.

Gene targeting in the silkworm by use of a baculovirus

The Bombyx mori fibroin light (L)-chain gene was cloned and the green fluorescent protein (GFP) gene inserted into exon 7. The chimeric L-chain-GFP gene was used to replace the polyhedrin gene of Autographa californica nucleopolyhedrovirus (AcNPV). This recombinant virus was used to target the L-chain-GFP gene to the L-chain region of the silkworm genome. Female moths were infected with the recombinant virus and then mated with normal male moths. Genomic DNA from their progenies was screened for the desired targeting event. This analysis showed that the chimeric gene had integrated into the L-chain gene on the genome by homologous recombination and was stably transmitted through generations. The chimeric gene was expressed in the posterior silk gland, and the gene product was spun into the cocoon layer.

Trapping cDNAs encoding secreted proteins from the salivary glands of the malaria vector Anopheles gambiae

The signal sequence trap method was used to isolate cDNAs corresponding to proteins containing secretory leader peptides and whose genes are expressed specifically in the salivary glands of the malaria vector Anopheles gambiae. Fifteen unique cDNA fragments, ranging in size from 150 to 550 bp, were isolated and sequenced in a first round of immunoscreening in COS-7 cells. All but one of the cDNAs contained putative signal sequences at their 5' ends, suggesting that they were likely to encode secreted or transmembrane proteins. Expression analysis by reverse transcription-PCR showed that at least six cDNA fragments were expressed specifically in the salivary glands. Fragments showing a high degree of similarity to D7 and apyrase, two salivary gland-specific genes previously found in Aedes aegypti, were identified. Of interest, three different D7-related cDNAs that are likely to represent a new gene family were found in An. gambiae. Moreover, three salivary gland-specific cDNA fragments that do not show similarity to known proteins in the databases were identified, and the corresponding full length cDNAs were cloned and sequenced. RNA in situ hybridization to whole female salivary glands showed patterns of expression that overlap only in part those observed in the culicine mosquito A. aegypti.

Precise excision and transposition of piggyBac in pink bollworm embryos

Transposable elements such as P, hobo, Hermes, mariner and Minos have been successfully harnessed as gene vectors to achieve the transformation of several dipteran species including Drosophila melanogaster, Ceratitis capitata and Aedes aegypti. Plasmid-based excision and transposition assays have been useful indicators of an element's ability to be mobilized in vivo and thus potentially serve as a transforming vector. We report that the transposable element piggyBac is capable of precise excision and transposition in the pink bollworm (Pectinophora gossypiella), a worldwide pest of cultivated cotton. Combined with a suitable marker gene, the piggyBac element may serve as a vector for germline transformation in this and (potentially) other lepidopteran species.

Promoter-directed expression of recombinant fire-fly luciferase in the salivary glands of Hermes-transformed Aedes aegypti

Molecular genetic analyses of biological properties characteristic of insect vectors of disease, such as hematophagy and competence for pathogens, require the ability to isolate and characterize genes involved in these processes. We have been working to develop molecular approaches for studying the promoter function of genes that are expressed specifically in the adult salivary glands of the yellow fever mosquito, Aedes aegypti. Genomic DNA fragments containing cis-acting promoter elements from the Maltase-like I (MalI) and Apyrase (Apy) genes were cloned so as to direct the expression of the reporter gene, luciferase (luc). The function of the promoters was assayed transiently in cultured insect cells and by germ-line transformation of Ae. aegypti. MalI and Apy DNA fragments consisting of at least 650 nucleotides (nt) of DNA immediately adjacent to the 5'-end of the initiation codon of the mosquito genes directed constitutive expression of the luc reporter gene in cultured cells. When introduced into Ae. aegypti chromosomes, approximately 1.5 kilobases (kb) of each promoter were able to direct the predicted developmental-, sex- and tissue-specific expression of the reporter gene in patterns identical to those determined for the respective endogenous genes.

Molecular and genetic ecotoxicologic approaches to aquatic environmental bioreporting

Molecular and population genetic ecotoxicologic approaches are being developed for the utilization of arthropods as bioreporters of heavy metal mixtures in the environment. The explosion of knowledge in molecular biology, molecular genetics, and biotechnology provides an unparalleled opportunity to use arthropods as bioreporter organisms. Interspecific differences in aquatic arthropod populations have been previously demonstrated in response to heavy metal insult in the Arkansas River (AR) California Gulch Superfund site (CGSS). Population genetic analyses were conducted on the mayfly Baetis tricaudatus. Genetic polymorphisms were detected in polymerase chain reaction amplified 16S mitochondrial rDNA (a selectively neutral gene) of B tricaudatus using single-strand conformation polymorphism analysis. Genetic differences may have resulted from impediments to gene flow in the population caused by mortality arising from exposure to heavy metal mixture pollution. In laboratory studies a candidate metal-responsive mucinlike gene, which is metal and dose specific, has been identified in Chironomus tentans and other potential AR-CGSS bioreporter species. Population genetic analyses using the mucinlike gene may provide insight into the role of this selectable gene in determining the breeding structure of B. tricaudatus in the AR-CGSS and may provide mechanistic insight into determinants of aquatic arthropod response to heavy metal insult. Metal-responsive (MR) genes and regulatory sequences are being isolated, characterized, and assayed for differential gene expression in response to heavy metal mixture pollution in the AR-CGSS. Identified promoter sequences can then be engineered into previously developed MR constructs to provide sensitive in vitro assays for environmental bioreporting of heavy metal mixtures. The results of the population genetic studies are being entered into an AR geographic information system that contains substantial biological, chemical, and geophysical information. Integrated spatial, structural, and temporal analyses of these parameters will provide invaluable information concerning environmental determinants that restrict or promote gene flow in bioreporter populations.