Downregulation of aquaporin-2 parallels changes in renal water excretion in unilateral ureteral obstruction

In bilateral ureteral obstruction, both aquaporin-2 (AQP2) levels and urinary concentrating capacity are markedly reduced. However, the mechanisms involved in AQP2 downregulation are unknown. In rats with unilateral ureteral obstruction (UUO) the relative role of intrarenal and systemic factors can be evaluated. Semiquantitative immunoblotting revealed a marked decrease in AQP2 in obstructed kidneys to 23 +/- 7% (n = 9) of sham levels. This downregulation persisted 24 h after release of UUO. Furthermore, there was a significant but less extensive downregulation of AQP2 in the nonobstructed kidneys to 75 +/- 7% (n = 9) of sham levels. Consistent with impairment of collecting duct water reabsorption, free water clearance was greatly elevated in the obstructed kidneys (-2 +/- 1 microliter-min-1.kg-1, determined immediately after release) and only moderately elevated in nonobstructed kidneys (-44 +/- 5 microliters.min-1.kg-1) compared with sham-operated controls (-59 +/- 3 microliters.min-1.kg-1). Also AQP2 mRNA levels were reduced in obstructed kidneys. Immunocytochemistry confirmed the marked decrease in AQP2 expression in obstructed kidneys. In nonobstructed kidneys AQP2 was predominantly found in intracellular vesicles, which together with the reduced expression and elevated free water clearance strongly suggests a role of AQP2 in the observed compensatory diuresis from nonobstructed kidneys. The much lower AQP2 protein and mRNA levels in obstructed vs. nonobstructed kidneys are consistent with intrarenal factors playing a major role for downregulation of AQP2.

Comparisons of genetic variability and genome structure among mosquito strains selected for refractoriness to a malaria parasite

Restriction fragment length polymorphism (RFLP) markers were used to evaluate Aedes aegypti genome structure and genetic variability within and between substrains selected for different levels of refractoriness to the malaria parasite, Plasmodium gallinaceum. The MOYO-R substrain was previously selected for complete refractoriness and the MOYO-IS substrain for intermediate susceptibility from the Moyo-In-Dry (MOYO) strain by selective inbreeding (F = 0.5). Eighteen mapped RFLP markers were used to provide coverage of the mosquito genome. The two substrains showed reduced genetic diversity compared with the MOYO strain, including significant reductions in mean heterozygosity, number of alleles per locus, and proportion of polymorphic loci. Genetic differentiation between the two substrains was statistically significant, as reflected by differences in allele frequencies. Significant pairwise linkage disequillbrium among the RFLP loci was detected in all three strains, most evidently in the MOYO strain. This is surprising because the RFLP loci examined are separated by large map distances, and therefore linkage disequilibrium should decay to zero after many generations of laboratory culture. Our hypothesis to explain this phenomena is that lack of recombination, or low recombination rates in some regions of the A. aegypti genome, is a result of chromosome inversions. Finally, we used graphical genotyping, wherein whole genome genotypic information for individual mosquitoes is represented in a simple graphic format, to illustrate genome structure and allelic variation within and among the mosquito strains. Our analysis revealed an apparent chromosomal deletion on chromosome 3 for some individuals in the MOYO strain and MOYO-IS substrain.

Phenoloxidase activity in the reproductive system and egg masses of the pulmonate gastropod, Biomphalaria glabrata

Phenoloxidase (PO) activity in the albumen gland (AG) and egg masses (EM) of Biomphalaria glabrata was assessed using high-performance liquid chromatography combined with electrochemical detection and colorimetric techniques. Both AG and EM extracts catalyzed the hydroxylation of L-tyrosine (monophenol oxidase activity, MPO) and oxidation of L-dopa (diphenol oxidase activity, DPO). However, no PO activity was found in the ovotestis. Both MPO and DPO activities in AG and EM were significantly inhibited by 1-phenyl-2-thiourea and inactivated by boiling. Approximately 35% of MPO and 44% of DPO activities were detected in the soluble fraction of homogenized EM, in contrast to that of homogenized AG, which contained about 5% and 12%, respectively, of MPO and DPO activities. N-acetyl-dopamine, a diphenolic compound, enhanced the hydroxylation of tyrosine by the PO. The presence of both MPO and DPO activities also was confirmed by the accelerated accumulation of dopachrome during incubation of EM extracts with L-tyrosine in the absence of ascorbate. Temperature and pH optima for this enzyme were 30 degrees C and 7.5, respectively. The potential roles of PO in egg formation in B glabrata are discussed.

Aedes aegypti: induced antibacterial proteins reduce the establishment and development of Brugia malayi

The effect of host immune activation on the development of Brugia malayi in one susceptible and four refractory strains of Aedes aegypti and in Armigeres subalbatus was assessed. A. aegypti that were immune activated by the injection of saline or bacteria 24 hr before feeding on a B. malayi-infected gerbil had significantly reduced prevalences and mean intensities of infection from those of naive controls when exposed to bloodmeals with low (105 mf/20 microliters) and medium (160 mf/20 microliters) microfilaremias. At a higher microfilaremia (237 mf/20 microliters) there were no significant differences in mean intensities, suggesting that the number of parasites ingested may affect the host's ability to mount an effective defense response. Because the major immune proteins in A. aegypti are defensins, we did Northern analyses of fat body RNA 8 hr after immune activation or bloodfeeding. All mosquitoes demonstrated rapid transcriptional activity for defensins following immune activation by intrathoracic inoculation with either saline or bacteria. However, no strain of A. aegypti, susceptible or refractory to B. malayi, nor Ar. subalbatus produced defensin transcripts after bloodfeeding on an uninfected or a B. malayi-infected gerbil. These data suggest that inducible immune proteins of mosquitoes can reduce the prevalence and mean intensity of infections with ingested parasites, but these proteins are not expressed routinely after parasite ingestion and midgut penetration and probably do not contribute to existing refractory mechanisms. Immune proteins such as defensins, however, represent potential candidates to genetically engineer mosquitoes for resistance to filarial worms.

Biogenic monoamines in the freshwater snail, Biomphalaria glabrata: influence of infection by the human blood fluke, Schistosoma mansoni

The biogenic monoamines, serotonin (5-HT), dopamine (DA) and L-dopa were measured using high performance liquid chromatography with electrochemical detection (HPLC-ED) in the extracts of the central nervous system (CNS) and plasma of uninfected freshwater snails, Biomphalaria glabrata, and in snails at 7, 14, 21 and 28 days postexposure (PE) to the miracidia of the human blood fluke, Schistosoma mansoni. Relative to age-matched uninfected snails, a general depression of biogenic amine levels was observed in the plasma (cell-free haemolymph) and the CNS of infected snails, especially during the latter phase of the prepatency period. Significant decreases were first observed in the CNS of infected snails beginning at Day 14 PE for DA and 5-HT and Day 21 PE for L-dopa. Parasite-exposed snails also exhibited an early and persistent suppression of plasma 5-HT concentrations, starting at 7 days PE and continuing throughout the infection test period. In order to determine the effect of 5-HT on reproduction and, thereby, establish a possible relationship between the observed parasite-induced reduction in 5-HT levels and parasitic castration, the effect of exogenous 5-HT on individual infected and uninfected B. glabrata was investigated. Repeated treatment with 10 microM 5-HT promoted both ovulation and oviposition in B. glabrata. Snails treated with 5-HT consistently layed more eggs than did sham-treated controls. Infected snails that were treated with 5-HT exhibited similar egg-laying rates as those of both serotonin-treated and untreated, uninfected snail groups, thus reversing the castrating effects of larval infection. These findings suggest that 5-HT acts as a stimulant for egg production in B. glabrata, and that parasitic castration may be due, at least in part, to larval-induced suppression of 5-HT in the snail's CNS and plasma during the course of infection with S. mansoni.

Mosquito dopa decarboxylase cDNA characterization and blood-meal-induced ovarian expression

Dopa decarboxylase (DDC) functions in insect catecholamine biochemistry to produce materials essential for cross-linking reactions that result in tanning and/or melanization, include tanning of the mosquito egg chorion and encapsulation of parasites. We have cloned Ddc from the mosquito, Aedes aegypti, and studied its expression in response to blood-feeding, which initiates events necessary for egg maturation in mosquitoes. The Ae. aegypti Ddc cDNA was isolated via heterologous screening using a clone from Drosophila melanogaster. A resulting 1.87 kilobase (kb) clone was sequenced to reveal an open reading frame of 1464 bp, as well as 5'- and 3'-untranslated segments. The inferred amino acid sequence of this clone shares 81% identity with the published Drosophila Ddc cDNA, including complete identity with twenty-four contiguous amino acids encompassing the pyridoxal-5-phosphate cofactor binding domain. Analysis of an F2 intercross population derived from a parental cross between two Ae. aegypti strains (Hamburg and Moyo-In-Dry) allowed us to map Ddc to a locus on linkage group 2. Expression studies demonstrated the presence of a 2.1 kb message, the majority of which occurs in the ovaries where Ddc-specific mRNA is up-regulated in response to ingestion of a blood meal. The potential for egg-tanning in anautogenous mosquitoes as a model for understanding specific genetic events in the regulation of catecholamine metabolism is addressed.

Influence of anesthetics on the peripheral blood microfilaremia of Brugia malayi in the Mongolian jird, Meriones unguiculatus

The effects of anesthetics on the peripheral blood microfilaremia of Brugia malayi in Meriones unguiculatus were investigated. Microfilaremias were assessed by orbital puncture prior to and following the use, either individually or in tandem, of ether, Rompun, Ketaset, and sodium pentobarbital. Results indicate that the peripheral microfilaremia varied dramatically, depending on the anesthetic administered. Although microfilaremias were not affected by an initial ether exposure, counts of microfilariae increased significantly when jirds received Rompun and Ketaset, or Ketaset alone. Administration of sodium pentobarbital did not increase the number of microfilariae observed in the peripheral blood. The mode of action differs between these drugs and is likely responsible for the different effects observed. Consequently, studies involving vector-parasite interactions should take precautions to prevent parasite-induced vector mortality due to the ingestion of large numbers of microfilariae induced in the peripheral bloodstream by certain anesthetics.

Involvement of peroxidase in chorion hardening in Aedes aegypti

Peroxidase activity is detectable in Aedes aegypti ovaries, containing developing eggs, at 24 h following blood feeding, and peak peroxidase activity is reached at 36-48 h after the blood-meal. Peroxidase is associated with the chorion layer in mature eggs and the majority of the enzyme is released from the chorion layer by treating the isolated chorion fraction with SDS/urea. Analysis of the SDS/urea solubilized chorion proteins using SDS-PAGE with tropolone/H2O2 or dopa staining verified the presence of both peroxidase and phenol oxidase in the released chorion proteins. The molecular weight of chorion peroxidase is about 61,000 Da as determined by SDS-PAGE analysis. Incubation of the solubilized chorion proteins with tyrosine and H2O2 produces dityrosine, and hyrolysis of hardened egg chorion results in the detection of dityrosine and trityrosine in the chorion hydrolysate. Data suggest that chorion peroxidase is involved in the hardening of the mosquito egg chorion by catalyzing the formation of ditryrosine through tyrosine residues on structural proteins. The overall hardening of the A. aegypti egg chorion includes both peroxidase-mediated chorion protein crosslinking through dityrosine formation and phenol oxidase-catalyzed chorion melanization.

Monoclonal antibodies against Manduca sexta hemocytes bind Aedes aegypti hemocytes: characterization of six monoclonal antibodies that bind hemocytes from both species

The mechanisms by which hemocytes mediate a mosquito's defense response to parasites or pathogens are not well understood. This is due in part to difficulty in collecting intact mosquito hemocytes for experiments and to a lack of reagents, such as antibodies. Our objectives were to collect adult Aedes aegypti hemocytes under conditions suitable for immunofluorescence microscopy, and to test whether monoclonal antibodies, generated against larval Manduca sexta hemocytes, bind adult Ae. aegypti hemocytes. We present immunofluorescence micrographs of M. sexta and Ae. aegypti hemocytes stained by six monoclonal antibodies. Two antibodies, MS11 and MS32, immunolocalized to hemocyte nuclei in both species. On Western blots, these antibodies generate one signal at approximately 40 kDa and four others between 10 and 25 kDa. Immunofluorescence staining patterns of the other four antibodies were more complex. That these antibodies bind hemocytes from both species suggests significant molecular similarities exist between hemocytes from evolutionarily divergent species.

Aedes aegypti: a quantitative trait locus (QTL) influencing filarial worm intensity is linked to QTL for susceptibility to other mosquito-borne pathogens

Because intensity of infection was significantly increased in a substrain of Aedes aegypti selected for susceptibility to the filarial worm, Brugia malayi, experiments were designed to assess numbers of microfilariae (mf) ingested and midgut penetration by mf in this susceptible substrain as compared to a refractory substrain selected from the same parental stock. Refractory mosquitoes ingested significantly fewer mf than susceptible mosquitoes and significantly fewer numbers of mf penetrated through refractory midguts as compared to susceptible midguts. In 16.7% of the refractory midguts, no mf were able to penetrate the midgut and in three refractory mosquitoes over 250 mf were ingested, but no mf penetrated the midgut. These results indicate that permissiveness of the midgut for penetration by microfilariae can determine not only parasite intensity, but also prevalence of infection. The genetic basis for ingestion of mf and midgut penetration was assessed using restriction fragment length polymorphism markers and quantitative trait loci (QTL) mapping. This mapping identified a QTL on chromosome 2, idb[2,LF181] (idb, intensity determinant for Brugia), that seems to influence ingestion ability. This QTL is linked to a previously identified QTL for susceptibility to B. malayi, fsb[2,LF98], as well as to loci for susceptibility to the malaria parasite, Plasmodium gallinaceum, and yellow fever virus. These results suggest that this region of chromosome 2 contains one or more genes that influence susceptibility of A. aegypti to several mosquito-transmitted pathogens.

Insect immunity: isolation of three novel inducible antibacterial defensins from the vector mosquito, Aedes aegypti

The injection of Escherichia coli and Micrococcus luteus into the hemocoel of Aedes aegypti induces a potent antibacterial activity in the hemolymph. We have purified and fully characterized three 40-residue antibacterial peptides from the hemolymph of bacteria-challenged mosquitoes that are absent in naive mosquitoes. The peptides are potently active against Gram-positive bacteria and against one of the Gram-negative bacteria that were tested. The amino acid sequences clearly show that the three peptides are novel isoforms of the insect defensin family of antibacterial peptides. They differ from each other by one or two amino acid residues. We present here the complete amino acid sequences of the three isoforms and the activity spectrum of the predominant Aedes defensin.

Biochemical pathway of melanotic encapsulation of Brugia malayi in the mosquito, Armigeres subalbatus

The mosquito, Armigeres subalbatus, is naturally resistant to the filarial worm, Brugia malayi, and microfilariae (mf) penetrating the midgut are killed by melanotic encapsulation reactions in the hemocoel within 48 h following ingestion. This vector-parasite system was used to assess changes in hemolymph tyrosine, tyrosine derivatives, and catecholamine-metabolizing enzyme activities using high pressure liquid chromatography with electrochemical detection (HPLC-ED) during melanotic encapsulation reactions against mf. Tyrosine and dopa were detected in the hemolymph of both control and immune-activated (mf-exposed) mosquitoes, but not dopamine or N-acetyl dopamine (NADA). Tyrosine was significantly increased in immune-activated mosquitoes at 6 and 12 h post blood feeding, but was depleted following intrathoracic inoculation of mf in the absence of a blood meal. Dopa also was elevated in immune-activated mosquitoes at 6, 12, and 24 h post-exposure to mf. There were significant increases in phenol oxidase (PO) and dopa decarboxylase (DDC) activities in immune-activated mosquitoes as compared to controls, and these elevated activities were correlated with changes in tyrosine and dopa levels in the hemolymph. No significant differences in N-acetyl transferase (NAT) and dopachrome conversion enzyme (DCE) activities between control and immune-activated mosquitoes were observed. The possible roles these molecules play in melanotic encapsulation reactions of A. subalbatus against mf are discussed.

Restriction fragment length polymorphism mapping of quantitative trait loci for malaria parasite susceptibility in the mosquito Aedes aegypti

Susceptibility of the mosquito Aedes aegypti to the malarial parasite Plasmodium gallinaceum was investigated as a quantitative trait using restriction fragment length polymorphisms (RFLP). Two F2 populations of mosquitoes were independently prepared from pairwise matings between a highly susceptible and a refractory strain of A. aegypti. RFLP were tested for association with oocyst development on the mosquito midgut. Two putative quantitative trait loci (QTL) were identified that significantly affect susceptibility. One QTL, pgs[2,LF98], is located on chromosome 2 and accounted for 65 and 49% of the observed phenotypic variance in the two populations, respectively. A second QTL, pgs[3,MalI], is located on chromosome 3 and accounted for 14 and 10% of the observed phenotypic variance in the two populations, respectively. Both QTL exhibit a partial dominance effect on susceptibility, wherein the dominance effect is derived from the refractory parent. No indication of epistasis between these QTL was detected. Evidence suggests that either a tightly linked cluster of independent genes or a single locus affecting susceptibility to various mosquito-borne parasites and pathogens has evolved near the LF98 locus; in addition to P. gallinaceum susceptibility, this general genome region has previously been implicated in susceptibility to the filarial nematode Brugia malayi and the yellow fever virus.

Hemocyte alterations during melanotic encapsulation of Brugia malayi in the mosquito Armigeres subalbatus

The involvement of hemocytes in melanotic encapsulation reactions against Brugia malayi was assessed in Armigeres subalbatus. Hemocyte populations, epitope changes, phenol oxidase (PO) activity, and the presence of an 84-kDa polypeptide were investigated in mosquitoes exposed to a B. malayi-infective bloodmeal (= immune-activated), in mosquitoes given a noninfective bloodmeal (= controls), in nonbloodfed mosquitoes (= naive), or in some combination of these. Total hemocyte populations in immune-activated mosquitoes significantly decreased at 24 hr postbloodmeal (PB) as compared with controls. At 48 and 72 hr PB, hemocyte population levels in immune-activated mosquitoes increased to control levels. Epitope changes, as indicated by wheat germ agglutinin (WGA) binding, also were observed. There was a significant increase in the percentage of hemocytes binding WGA in immune-activated mosquitoes at 24 hr PB as compared with controls. Furthermore, the activity of hemocyte PO, an enzyme involved in the melanotic encapsulation pathway, was significantly elevated at 12 hr PB in immune-activated mosquitoes as compared with controls. Analysis for the presence of an 84-kDa polypeptide in A. subalbatus indicates that a 2.0-kb message in total RNA hybridized to D6.12, an Aedes aegypti cDNA encoding an 84-kDa polypeptide that is associated with melanotic encapsulation responses. The hybridization of D6.12 to RNA was not greater in immune-activated as compared to control A. subalbatus, as has been observed in A. aegypti. Results indicate that these hemocyte changes correspond in time with the melanotic encapsulation reactions of A. subalbatus against filarial worms.

Comparative linkage maps for the mosquitoes, Aedes albopictus and Ae. aegypti, based on common RFLP loci

Aedes albopictus and Aedes aegypti are members of the mosquito family Culicidae and share a haploid chromosome complement of three. Although a genetic linkage map based on restriction fragment length polymorphism (RFLP), markers exists for Ae. aegypti, the extent of synteny and linkage order conservation between the two species was unknown. A comparative linkage map for Ae. albopictus was constructed based mainly on cDNA clones from Ae. aegypti. Nearly all Ae. aegypti probes hybridized to Ae. albopictus DNA at high stringency. For eighteen RFLP markers tested, the linkage group and linear order appears to be identical for the two species. 78% of the loci tested exhibited significant deviations from the expected segregation ratio in at least one of the test crosses. An excess of heterozygote genotypes was recovered with most loci. This probably reflects the effects of lethal loci on survival of F2 progeny homozygous for the parental genotypes. These results demonstrate that comparative linkage maps based on common DNA markers provide a basis for rapidly developing linkage maps for various mosquito species, and the opportunity to examine the significance and function of orthologous quantitative trait loci associated with mosquito vector competence for disease transmission.

Dopachrome conversion activity in Aedes aegypti: significance during melanotic encapsulation of parasites and cuticular tanning

Phenol oxidase (PO) and dopachrome conversion enzyme (DCE) were partially purified from Aedes aegypti larvae by ammonium sulfate fractionation. PO from A. aegypti functions in the hydroxylation of monophenols (e.g., tyrosine and tyramine) to their related o-diphenols, and the oxidation of o-diphenols (e.g., L-dopa, dopamine, N-acetyldopamine) to their respective o-quinones. Partially purified DCE showed high specificity toward dopachrome generated from dopa with the L-configuration. The combined effects of PO and DCE significantly accelerated melanization pathways when L-dopa was used as substrate. Significant DCE activity also was detected in hemolymph samples from adult, female A. aegypti, and undoubtedly plays a role in melanotic encapsulation reactions.

Aedes aegypti: characterization of a hemolymph polypeptide expressed during melanotic encapsulation of filarial worms

We report on the initial characterization of an 84-kDa polypeptide that is differentially expressed in Aedes aegypti during melanotic encapsulation immune reactions against filarial worms. [35S]Methionine-labeled hemolymph from mosquitoes inoculated with saline, parasites that are melanized, or parasites that are not melanized was analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Results show that the level of the 84-kDa polypeptide increases considerably in those mosquitoes undergoing encapsulation reactions against parasites but remains down-regulated in those mosquitoes exposed to parasites that are not melanized or are undergoing wound healing responses (saline-inoculated). Experiments involving glycosidase treatment of hemolymph samples indicate that this polypeptide is not heavily glycosylated. Amino acid microsequencing was performed and two internal sequence fragments (15 continuous amino acids and 12 noncontinuous amino acids) were obtained. Analysis of these sequences to known sequences in a protein database did not yield any conclusive information as to the identify of the 84-kDa polypeptide. Therefore, degenerate oligonucleotide primers were designed, based on the sequence of the 15-amino-acid fragment, and used with the polymerase chain reaction (PCR) to amplify from A. aegypti genomic DNA the region between the primers. The PCR product was cloned and sequenced to verify that the nucleic acid sequence matched the known protein sequence. Screening of an A. aegypti cDNA library with this small PCR-generated clone resulted in the selection of an approximately 540-bp clone. Northern analysis with this larger cDNA clone indicates that it hybridizes to an approximately 2.0-kb message that is differentially expressed in mosquitoes undergoing melanotic encapsulation reactions against filarial worms. Furthermore, sequencing of this approximately 540-bp clone showed that it contained the 15-amino-acid sequence that had been used to design the degenerate PCR primers, indicating that an appropriate clone was selected. However, sequence analysis of this clone at the protein and nucleic acid level did not provide any conclusive answers to the identity or function of the 84-kDa polypeptide.

Reinterpretation of the genetics of susceptibility of Aedes aegypti to Plasmodium gallinaceum

Several studies have demonstrated a genetic basis for variation in susceptibility of Aedes aegypti to Plasmodium gallinaceum. Although 25 yr ago it was reported that P. gallinaceum susceptibility in Ae. aegypti is determined primarily by a single autosomal dominant gene, evidence for additional genetic factors has emerged. Two sublines, 1 refractory and 1 of intermediate susceptibility to P. gallinaceum, have been selected from the Moyo-In-Dry strain (MOYO) of Ae. aegypti. Prior to selection, the MOYO population was 20.3% refractory. Genetic crosses of the highly susceptible Rockefeller strain (ROCK) and the 2 selected sublines of the MOYO strain provide evidence for a complex mode of inheritance of Plasmodium susceptibility in Ae. aegypti.

Chromosomal mapping of two loci affecting filarial worm susceptibility in Aedes aegypti

Two quantitative trait loci (QTL) affecting susceptibility of the mosquito Aedes aegypti to the filarial worm parasite Brugia malayi were identified using restriction fragment length polymorphism (RFLP) markers. The first locus, fsb[1,LF178], resides within a 10 cM interval on chromosome 1 and exhibits a recessive effect with respect to susceptibility. The second locus, fsb[2,LF98], resides within a 9 cM interval on chromosome 2 and exhibits an additive effect on susceptibility. Significant epistasis was detected between these loci, although the effect of fsb[2,LF98] was dependent on the genetic background of the mosquito strains. Suggestions for a standard QTL nomenclature are included.

The suitability of restriction fragment length polymorphism markers for evaluating genetic diversity among and synteny between mosquito species

Restriction fragment length polymorphism (RFLP) markers derived from the yellow fever mosquito, Aedes aegypti, were used in hybridizations to genomic DNA of the following mosquito species: Ae. albopictus, Ae. togoi, Armigeres subalbatus, Culex pipiens, and Anopheles gambiae. Interspecific hybridization with Ae. aegypti probes varied from 50% (An. gambiae) to 100% (Ae. albopictus) under high stringency conditions. We demonstrated the usefulness of using RFLP profiles to examine genetic diversity between mosquito populations; Ae. aegypti RFLP markers were used to examine genetic relatedness between 10 laboratory strains of Ae. aegypti as well as between nine populations representing four Cx. pipiens subspecies. These results indicate that many Ae. aegypti RFLP markers should have direct applicability in gaining a better understanding of genome structure in other mosquito species, including RFLP linkage mapping and determinations of genetic relatedness among field populations.

Reproductive costs associated with resistance in a mosquito-filarial worm system

The mosquito Armigeres subalbatus can encapsulate and kill > 80% of Brugia malayi microfilariae (mf) within 36 hr following ingestion. The cascade of biochemical events constituting this melanotic encapsulation response is also important in other mosquito biological events, including egg-chorion tanning. Certain biochemical entities, including a tyrosine precursor, are thought to be shared among these biological activities. Because of this purported tyrosine link, and because the blood meal both initiates egg development and is the source of mf, we evaluated the possibility that reproductive cost is incurred by the resistant host when undergoing a response to mf acquired in an infected blood meal. Mean time to oviposition was significantly longer for mosquitoes responding to parasites than for controls (77.7 versus 66.5 hr). Tyrosine levels in ovaries from infected mosquitoes were less than half those of controls at 24 and 48 hr, and were still significantly reduced at 72 hr following blood feeding. Ovary development, assessed via measurements and total protein content, also was delayed significantly in the experimental group, with ovary width and protein content never attaining levels found in control mosquitoes. Sections from 24-hr post-blood meal ovaries demonstrated that the normal processes of egg development, including vitelline accumulation, was drastically altered as well. The biological implications of these results are considered.

Linkage map for Aedes aegypti using restriction fragment length polymorphisms

We report construction of a genetic linkage map for the mosquito, Aedes aegypti, based on restriction fragment length polymorphisms (RFLPs). The map consists of 50 DNA markers that identify 53 loci covering 134 map units across three linkage groups. Determination of linkage associations between RFLP markers and several mutant marker loci allowed for partial integration of the RFLP markers with an existing classical genetic linkage map for A. aegypti. The RFLP markers include 42 random cDNA clones, three random genomic DNA clones, and five cDNA clones of known genes. We discuss the influence of autosomal sex determination, characteristic of culicine mosquitoes, in relation to its observed influence on segregation ratios. This has important ramifications for future efforts to identify quantitative trait loci associated with the ability of these mosquitoes to transmit various pathogens and parasites to man and other animals.

Further evidence that the genes controlling susceptibility of Aedes aegypti to filarial parasites function independently

Comparisons were made of in vivo labeled polypeptides from Aedes aegypti strains refractory to either Brugia malayi or Dirofilaria immitis. There does not seem to be a generalized "anti-parasite" polypeptide response that mosquitoes refractory to filarial worm infection produce following bloodfeeding. Instead, it seems that any response produced by these mosquitoes is localized to the tissue in which the filarial parasite develops.

Variation in Aedes aegypti mRNA populations related to strain, sex, and development

Translation products were used to monitor changes in gene expression between different strains and developmental stages of Aedes aegypti. Total RNA was isolated from fourth stadium larvae, male and female pupae, and male and female adults collected at fixed time intervals following pupation and ecdysis. Differences in RNA populations were assessed by in vitro translation followed by one- and two-dimensional polyacrylamide gel electrophoresis and fluorography. Variations in gene expression between sexes and during development were examined in Liverpool (LVP) and Rockefeller (RKF) Ae. aegypti strains. Sex-related differences consisted primarily of differing lengths of expression for certain polypeptides, although two-dimensional electrophoresis revealed changes in intensity of a 44-kD polypeptide with a pI of 7.9 between males and females. Fourth stadium larvae, pupae, and adults expressed different translation products, which probably correlated with developmental differences. Strain-related differences were observed between LVP and RKF.

Relationship of hemolymph phenol oxidase and mosquito age in Aedes aegypti

Monophenol oxidase (MPO) and diphenol oxidase (DPO) activity in hemocytes and cell-free plasma perfused from 7-, 14-, 21-, and 28-day-old Aedes aegypti mosquitoes were compared. A progressive decrease of enzyme activity was detected as mosquito age increased, and this decrease was significant in both hemocytes and cell-free plasma when mosquitoes were 28 days old as compared with that found in 7-day-old mosquitoes. There was no significant difference in total hemolymph protein as mosquito age increased. Although this decreased MPO and DPO activity might be partially responsible for the reduced immune response against filarial worms previously reported for older mosquitoes, other factors undoubtedly play a significant role.