Hormonal effects on insects and other endoparasites in vitro

Mosquito biology. Evolution of sexual traits influencing vectorial capacity in anopheline mosquitoes

The availability of genome sequences from 16 anopheline species provides unprecedented opportunities to study the evolution of reproductive traits relevant for malaria transmission. In Anopheles gambiae, a likely candidate for sexual selection is male 20-hydroxyecdysone (20E). Sexual transfer of this steroid hormone as part of a mating plug dramatically changes female physiological processes intimately tied to vectorial capacity. By combining phenotypic studies with ancestral state reconstructions and phylogenetic analyses, we show that mating plug transfer and male 20E synthesis are both derived characters that have coevolved in anophelines, driving the adaptation of a female 20E-interacting protein that promotes oogenesis via mechanisms also favoring Plasmodium survival. Our data reveal coevolutionary dynamics of reproductive traits between the sexes likely to have shaped the ability of anophelines to transmit malaria.

Molecular characterization of thyroid hormone receptor beta from Schistosoma japonicum and assessment of its potential as a vaccine candidate antigen against schistosomiasis in BALB/c mice

Background

Thyroid hormones (TH) modulate growth, development and differentiation and metabolic processes by interacting with thyroid hormone receptors (THRs). The purpose of this study was to identify a novel thyroid hormone receptor beta encoding gene of Schistosoma japonicum (SjTHRβ) and to investigate its potential as a vaccine candidate antigen against schistosomiasis in BALB/c mice.

Methods

The full-length cDNA sequence of SjTHRβ, its gene organization, and its transcript levels were characterized, and the phylogenetic relationship between THR, RAR and RXR from other organisms were analysis, the ability of this protein binding to a conserved DNA core motif, and its potential as a vaccine candidate antigen against schistosomiasis in BALB/c mice were evaluated.

Results

The SjTHRβ cDNA was cloned, verified by 5’ and 3’ Rapid Amplification of cDNA Ends and shown to be polyadenylated at the 3’end, suggesting the transcript is full-length. SjTHRβ is homologous to THRs from other species and has a predicted conservative DNA binding domain and ligand binding domain that normally characterizes these receptors. A comparative quantitative PCR analysis showed that SjTHRβ was the highest expressed in 21d worms and the lowest in 7 d and 13 d schistosomula. The cDNA corresponding to DNA binding domain (SjTHRβ-DBD) and ligand binding domain (SjTHRβ-LBD) were cloned and subsequently expressed in E coli. The expressed proteins were used to immunize mice and generate specific serum against recombinant SjTHRβ (rSjTHRβ). Western blotting revealed that anti-rSjTHRβ-LBD serum recognized two protein bands in extracts from 21 d worm with molecular sizes of approximately 95 kDa and 72 kDa. Electrophoretic mobility shift assay (EMSA) analysis showed that rSjTHRβ-DBD could bind to a conserved DNA core motif. Immunization of BALB/c mice with rSjTHRβ-LBD could induce partial protective efficacy(27.52% worm reduction and 29.50% liver eggs reduction)against schistosome infection. Enzyme-linked immunosorbent assay showed that mice vaccinated with recombinant SjTHRβ-LBD (rSjTHRβ-LBD) generated increased levels of specific IgG, IgG1 and IgG2a antibody. Bio-plex analysis demonstrated that rSjTHRβ-LBD induced considerably higher levels of T helper 1 cytokines (IL-2, IL-12 and TNF-α) than T helper 2 cytokines (IL-10, IL-4), suggesting that rSjTHRβ-LBD vaccination could stimulate mixed Th1/Th2 types with Th1 dominant immune responses.

Conclusions

Our study presented here identified SjTHRβ as a new schistosome THR that might play an important role in host-parasite interaction and be a vaccine candidate for schistosomiasis.

Trichomonas vaginalis: dehydroepiandrosterone sulfate and 17beta-estradiol alter NTPDase activity and gene expression

We investigated the effect of dehydroepiandrosterone sulfate (DHEAS) and 17beta-estradiol on NTPDase activity in fresh clinical (VP60) and long-term-grown (30236 ATCC) isolates of Trichomonas vaginalis followed by NTPDase gene transcriptional analysis. ATP hydrolysis was activated in vitro by 17beta-estradiol (0.01-1.0microM) in the VP60 isolate. Treatment for 2h with 17beta-estradiol (0.01-1microM) promoted an inhibition in nucleotide hydrolysis in the 30236 isolate whereas the 12h-treatment promoted an activation of nucleotide hydrolysis in both isolates. ADP hydrolysis was inhibited in vitro by 1.0-5.0microM DHEAS in the ATCC isolate. The treatment with DHEAS (0.01-1.0microM) for 2h inhibited ATP and ADP hydrolysis in VP60; however, during a 12h-treatment with DHEAS, nucleotide hydrolysis was inhibited in both isolates. Two NTPDase orthologous (NTPDaseA and NTPDaseB) were identified and the treatment with DHEAS for 12h was able to inhibit mRNA NTPDaseA transcript levels from the VP60. These findings demonstrate that NTPDase activity and gene expression pattern are modulated by exposure to steroids in T. vaginalis.

Impact of naturally acquired Taenia solium cysticercosis on the hormonal levels of free ranging boars

In chronically infected BALBc/AnN male mice, Taenia crassiceps cysticercosis induces changes in the host's sex steroids hormone that lead to their estrogenization and deandrogenization, with possible repercussions on their susceptibility to infections. Here reported are the serum steroid levels in free range cysticercotic male boars. Therefore, the possible effects of Taenia solium cysticerci over the pig steroid levels were evaluated. Herein are described the sex steroids and cortisol levels of non-cysticercotic (n=25) and cysticercotic (n=22) adult boars, as diagnosed by tongue inspection, all free-ranging in a typical village of an endemic rural area in Mexico. A significant reduction of testosterone (P=0.022) and a likely one of 17beta-estradiol (P=0.08) levels were found in the cysticercotic boars in comparison with those non-cysticercotic, whilst no significant differences in the cortisol and DHEA levels were detected. Serum levels of specific antibodies did not correlate with infection nor with the levels of any of the hormones measured. Results suggest that T. solium cysticercosis significantly affects the hormonal status of its porcine host independently of their antibody response.

Schistosoma mansoni (Platyhelminthes, Trematoda) nuclear receptors: Sixteen new members and a novel subfamily

Nuclear receptors (NRs) are important transcriptional modulators in metazoans. Sixteen new NRs were identified in the Platyhelminth trematode, Schistosoma mansoni. Three were found to possess novel tandem DNA-binding domains that identify a new subfamily of NR. Two NRs are homologues of the thyroid hormone receptor that previously were thought to be restricted to chordates. This study brings the total number of identified NR in S. mansoni to 21. Phylogenetic and comparative genomic analyses demonstrate that S. mansoni NRs share an evolutionary lineage with that of arthropods and vertebrates. Phylogenic analysis shows that more than half of the S. mansoni nuclear receptors evolved from a second gene duplication. As the second gene duplication of NRs was thought to be specific to vertebrates, our data challenge the current theory of NR evolution.

Dehydroepiandrosterone decreases while cortisol increases in vitro growth and viability of Entamoeba histolytica

In vitro exposure of Entamoeba histolytica trophozoites to the sex steroids 17beta-estradiol, progesterone, and dehydrotestosterone had little effect on parasite viability or proliferation. However, treatment with the adrenal steroid dehydroepiandrosterone (DHEA) markedly inhibited parasite proliferation, adherence and motility, and at a certain dose it induced trophozoite lysis. The opposite effect on proliferation was found when the trophozoites were exposed to cortisol. Moreover, DHEA decreased while cortisol increased the parasite's DNA synthesis determined by 3H-thymidine incorporation. Trophozoite lysis by DHEA appeared to be caused by a necrotic rather than an apoptotic process, as observed in propidium iodide and terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling assays. A possible mechanisms of action was derived from experiments demonstrating that the activity of a putative 3-hydroxy-3-methyl glutaryl CoA reductase detected in trophozoite extracts was inhibited in the presence of DHEA. Contrary to its in vitro inhibitory effect, in vivo administration of DHEA to infected hamsters resulted in exacerbation of the amebic liver abscesses. These results demonstrated that androgen steroids act directly upon E. histolytica growth and viability, and may shed new light on some age and gender differences in disease progression, as well as finding application in the drug treatment of human amebiasis.

15 alpha-Hydroxytestosterone produced in vitro and in vivo in the sea lamprey, Petromyzon marinus

Prior research has shown that the testes of lampreys are able to synthesize 15-hydroxylated steroid hormones in vitro. Here we show that testes of the sea lamprey Petromyzon marinus L. are able to convert tritiated testosterone into tritiated 15alpha-hydroxytestosterone (15alpha-T) in high yield. The identity of the tritiated 15alpha-T has been confirmed by: co-elution with standard 15alpha-T on high performance liquid chromatography (HPLC); co-elution on thin layer chromatography (TLC); co-elution of acetylated tritiated and standard 15alpha-T on TLC; and strong binding to an antiserum developed against 15alpha-T. The strong reaction between the tritiated 15alpha-T and the antiserum has been used to develop a radioimmunoassay (RIA). The RIA operates over the range of 500-2pg per tube; and can be applied directly to plasma samples. This assay has been used to demonstrate that 15alpha-T is present in blood plasma of the sea lamprey. The concentrations of 15alpha-T in captive lamprey were found to be as follows (pg/ml; mean+/-SEM, n): parasitic stage (reproductively immature), <20, n=7; pre-ovulatory females, 156+/-30, n=8; ovulated females, 62+/-9, n=5; pre-spermiating males, 275+/-19, n=8; spermiating males, 216+/-48, n=8. When spermiating male plasma was fractionated on HPLC, immunoreactivity was found exclusively in the expected elution position of 15alpha-T. The biological significance of this steroid has yet to be established.

Inhibition of the larval ecdysis and emergence behavior of the parasitoid Cotesia congregata by methoprene

Parasitism of the tobacco hornworm, Manduca sexta, by the braconid wasp Cotesia congregata, induces developmental arrest of the host in the larval stage. During the final instar of the host, its juvenile hormone (JH) titer is elevated, preventing host metamorphosis. This study investigated the effects of hormonal manipulation of the host on the parasitoid's emergence behavior. The second larval ecdysis of the wasps coincides with their emergence from the host, and application of the juvenile hormone analogue methoprene to day 4 fifth instar hosts either delayed or totally suppressed the subsequent emergence of the wasps. Effects of methoprene were dose-dependent and no parasitoids emerged following treatment of host larvae with doses >50 &mgr;g. Parasitoids which failed to emerge eventually succumbed as unecydsed pharate third instar larvae in the hemocoel of the host. Effects of host methoprene treatment on parasitoid metamorphosis were also assessed, and metamorphic disruption occurred at much lower dosages compared with doses necessary to suppress parasitoid emergence behavior. The inhibitory effect of methoprene on parasitoid emergence behavior appears to be mediated by effects of this hormone on the synthesis or release of ecdysis-triggering hormone (ETH) in the parasitoid, the proximate endocrine cue which triggers ecdysis behavior in free-living insects. ETH accumulated in the epitracheal Inka cells of parasitoids developing in methoprene-treated hosts, suggestive of a lack of hormone release. Thus, the hormonal modulation of parasitoid emergence behavior appears to be complex, involving a suite of hormones including JH, ecdysteroid, and peptide hormones.

Ecdysteroids and oocyte development in the black fly Simulium vittatum

BACKGROUND

Oocyte development was studied in the autogenous black fly, Simulium vittatum (Diptera, Nematocera), a vector of Onchocerca volvulus, the causative agent of onchocerciasis.

RESULTS

Oocyte growth was nearly linear between adult eclosion and was complete by 72 hours at 21 degrees C. The oocyte became opaque at 14 hours after eclosion indicating the initiation of protein yolk deposition. The accumulation of vitellogenin was measured using SDS-PAGE. The density of the yolk protein bands at about 200 and 65 kDa increased during the first and second days after eclosion. The amount of protein in the 200 kDa band of vitellogenin, determined using densitometry, rapidly increased between 12 and 25 hours after eclosion. Ecdysteroid levels were measured using a competitive ELISA. Ecdysteroid levels increased rapidly and subsequently declined during the first day after eclosion.

CONCLUSION

These data show a correlation between the appearance of vitellogenin in the oocyte, and the rise in ecdysteroids. A possible relationship to molting of the nematode, Onchocerca volvulus, is discussed.

Hormones and nuclear receptors in schistosome development

A substantial but disparate body of evidence suggests that hormones affect the development of schistosomes within their definitive hosts. Here, Raymond Pierce and colleagues review such evidence for host steroid and thyroid hormones, and for ecdysteroids, and link this to the expanding knowledge of the nuclear receptors for these hormones. Phylogenetic analysis of the nuclear receptor superfamily and the characterization of the first schistosome nuclear receptors suggest that steroids and thyroid hormone probably act indirectly, or by pathways not involving the control of gene transcription. However, the probability that schistosome nuclear receptors exist for a variety of unique ligands opens up exciting possibilities for targeted drug development.

Growth-promoting effects of ecdysteroids and juvenile hormone on in vitro development of the larval endoparasitoid, Venturia canescens (Hymenoptera: Ichneumonidae)

We previously reported that lipophorin, fetal bovine serum (FBS), and 20-hydroxyecdysone (20-HE) are essential for the development of the larval endoparasitoid Venturia canescens larvae in vitro. The present study was undertaken to determine the optimal concentrations of those three substances in the MGM-450 medium, and to examine the hormonal effects of ecdysteroids and juvenile hormone (JH) on the development of the parasitoid larvae in vitro. When the culture was started with embryos at the post-germband stage, concentrations of 3 mg/ml of lipophorin and 20% of FBS were most suitable for the development of the parasitoid. The growth-promoting effect of 20-HE increased in a concentration-dependent manner and peaked at a concentration of 1 &mgr;g/ml. Excess concentration led to malformations of the larvae. Three other ecdysteroids, ecdysone, 2-deoxy-20-hydroxyecdysone, and polypodine B had the same effect, although their activity was lower than that of 20-HE. Cholesterol had no effect; most larvae failed to develop. When the medium was supplemented with JH, the duration of the developmental period was significantly shortened, but this hormone was not found to be essential.

Infection of mice lacking interleukin-7 (IL-7) reveals an unexpected role for IL-7 in the development of the parasite Schistosoma mansoni

A single intradermal administration of recombinant interleukin-7 (IL-7) has been shown to aggravate the course of murine schistosomiasis, to favor the development of Th2-associated antibodies specific for the parasite, and to alter migration kinetics and/or migratory route of the parasite within its vertebrate host. Here we show that after infection of IL-7-deficient mice with Schistosoma mansoni, the predominant parasite-specific humoral response follows a Th1 pattern, and the development of the parasite is greatly impaired. In IL-7-deficient mice, increased numbers of larvae reach the lungs and fewer larvae reach the liver, compared to control mice. In the absence of IL-7, female worms show an altered fecundity, leading to decreased numbers of eggs trapped in the tissues and to an amelioration of the pathology of the infected host. The most striking observation is the blockade of parasite growth in an IL-7-defective environment, leading to dwarf male and female worms. The results of this study have important implications for the role of IL-7 in the host-parasite relationship and show how parasites can disable or evade the host immune response.

Effects of lipophorin and 20-hydroxyecdysone on in vitro development of the larval endoparasitoid Venturia canescens (Hymenoptera: Ichneumonidae)

We previously reported that development of the embryos of the larval endoparasitoid Venturia canescens proceeded in the insect cell culture medium, MGM-450, and was promoted by the addition of a pupal extract from their host Galleria mellonella. The developmental promotion also was obtained by supplementing an equal amount of chicken egg yolk instead of the pupal extract to the medium. In this case, approximately 30% of the embryos developed into the second instar, but the value increased to more than 90% by treatment with 20-hydroxyecdysone. The medium supplemented with a G. mellonella pupal extract obtained by using Carlson's solution displayed growth-promoting ability, and in the extract, apolipophorin I was electrophoretically detected in large amounts. Both lipophorin purified from G. mellonella pupae and low density lipoprotein from chicken egg yolk acted as a growth-promoting substance for parasitoid development, although fetal bovine serum and 20-hydroxyecdysone were required as supplements to the medium for the expression of the ability. This indicated that lipophorin or lipophorin-transported lipids could act as a substance closely related to the growth-promoting factor(s) putatively involved in the host extract.

Nutrition and culture of entomophagous insects

This article reviews the current state of knowledge concerning the nutrition of entomophagous insects and other arthropods. Early nutritional investigations focused principally on the basic dietary and nutritional requirements for beneficial insects. Based on these findings, the first attempts were made to develop mass culture methods and to formulate artificial diets that would allow rearing of parasitoids and predators in the absence of host or prey, as well as the latter's food sources. Although limited success was achieved, these studies established the nutritional foundation for later advances. Recently, attention has focused on the interaction between nutrition, physiology, behavior, and ecology of the different life stages of entomophagous species within a unified concept of nutritional ecology. This approach has resulted in more comprehensive understanding of nutrition, which in turn has facilitated the continuous artificial culture of several parasites and predators. Additional studies have confirmed the importance of supplemental feeding of the adult stages of beneficial insects for maximizing reproduction and longevity. Applications of nutritional ecology to biological control are discussed.

Interaction of calyx fluid and venom from Microplitis croceipes (Braconidae) on developmental disruption of the natural host, Heliocoverpa zea, and two atypical hosts, Galleria mellonella and Spodoptera exigua

Polydnaviruses of many braconid and ichneumonid endoparasitoids play an important role in the successful parasitism of their hosts. The host's development is altered and its immune response is also suppressed. In this study, we compared the effects of calyx fluid and venom on the development of the natural host, Helicoverpa zea, and two atypical hosts that the parasitoid does not normally attack in nature, Galleria mellonella and Spodoptera exigua. The levels of calyx fluid and\or venom injected was 0.05, 0.1 and 0.2 female equivalents (FE)/larva. In H. zea, calyx fluid significantly reduced larval growth on day 5 post injection. Venom alone did not affect larval growth but it synergized the action of calyx fluid by reducing growth earlier and for a longer period after injection. Other effects of calyx fluid on the host, either alone or in combination with venom, were an increase in developmental period, and a reduction in percent emergence and weight of adult moths. The percentage of H. zea larvae that pupated was not affected by calyx fluid or venom. In Galleria mellonella, venom alone reduced larval growth comparable to calyx fluid and both tissues induced the effects on day 1 post injection. Other effects caused by calyx fluid or venom alone or the combination were a reduction in percent pupation and emergence, and the average adult weight. In S. exigua, high mortality occurred when 4th instar larvae were injected. Although the injection of larger fifth instars reduced overall mortality, the sham-injected larvae only gained weight during the first 24 hours after injection (from day 0 to day 1). However, adults were produced at all doses of calyx fluid or venom. The effects of the virus on development in this species were a prolongation of the larval stage and reduction of adult weight by calyx fluid in combination with venom. In conclusion, injections of calyx fluid and venom of Microplitis croceipes can differentially affect the growth and development of its natural host H. zea, and atypical host, G. mellonella, but only a minimal effect was observed in S. exigua.

Schistosoma mansoni: susceptibility differences between male and female mice can be mediated by testosterone during early infection

In murine Schistosoma mansoni infections, fewer adult worms develop in male than in female mice infected with the same number of cercariae. To evaluate a potential role for testosterone in this phenomenon, testosterone levels were manipulated in groups of CBA/J mice that were then infected and monitored for survival rates, worm burdens, organomegaly, and egg production. By 16 weeks of infection, more than 80% of mice in groups with low levels of testosterone (untreated females, castrated males, or carrier-treated castrates) were dead, while less than 40% of those in groups with high levels of testosterone (sham-castrated males, testosterone-treated castrates, or testosterone-treated female mice) succumbed to infection. The mean number of worms recovered from mice in the low testosterone level groups was comparable among groups, and significantly greater than that from those in high-testosterone-level groups. The degree of organomegaly observed correlated strongly with worm burden, but the number of hepatic eggs per female worm did not differ significantly between groups. When male mice were castrated or sham-castrated 5 weeks after S. mansoni infection, no significant differences in host survival occurred. Furthermore, female mice treated with testosterone demonstrated reduced worm burdens if the testosterone was given 10 days prior to infection but not if the testosterone was given 10 days or 5 weeks after infection. Thus, the host sex bias observed in parallel-infected male and female mice appears to be related to the presence of male gonadal tissue or testosterone early in infection, during the development of immature schistosomules.

Characterization of genes encoding members of the nuclear hormone receptor superfamily from Onchocerca volvulus

Several lines of evidence suggest that molting in parasitic nematodes is controlled through the action of steroid molting hormones, or ecdysones. In other organisms, the central mediator of steroid hormone action is the hormone receptor. These receptor molecules are members of a superfamily of proteins called the nuclear hormone receptor family. Using an oligonucleotide derived from the amino-acid sequence of the Drosophila melanogaster ecdysone receptor, genes encoding homologues of the nuclear hormone receptor family were identified in the genome of the human filarial parasite Onchocerca volvulus. The O. volvulus genome contains at least three genes that encode putative members of the nuclear hormone receptor superfamily. A complete cDNA for one of these genes, designated OvNHR-1, has been isolated and characterized. The OvNHR-1 cDNA was 2378 bp in length, and contained a single open reading frame of 1104 bp. The open reading frame encoded a peptide with all of the features characteristic of a member of the nuclear hormone receptor superfamily of proteins. OVNHR-1 appeared to be encoded by a single-copy gene. Expression of the mRNA corresponding to OvNHR-1 was developmentally regulated, with maximal expression occurring during early embryogenesis. The polypeptide encoded by the OvNHR-1 open reading frame is antigenic in a minority of individuals exposed to O. volvulus.

Embryonic development of an endoparasitoid, Microplitis croceipes (Hymenoptera: Braconidae) in cell line-conditioned media

Embryos of the parasitoid Microplitis croceipes develop from pregerm band stage to first larval instar in cell culture medium conditioned by a cell line (IPLB-LdFB) derived from fat body from an atypical host Lymantria dispar. However, the percentage of eggs that develop normally to the first larval instar stage is significantly less than for those maintained in IPL-52B medium conditioned with host fat body tissue. Therefore, we examined the capacity of five insect cell lines to promote growth and development of pregerm band eggs in five media, IPL-52B, TC-199, TC-100, Grace's, and ExCell 400. The developmental response of M. croceipes was dependent both on the cell line and the cell culture medium used. TC-100, TC-199, and Grace's media promoted development to the germ band stage without the need for conditioning with host tissue. IPL-52B supported development to the germ band stage when a defined lipid concentrate was added. In IPL-52B medium, the IPLB-LdFB cell line promoted a significantly higher number of eggs developing to germ band relative to the other cell lines; however, none of the cell line-conditioned IPL-52B medium significantly stimulated egg hatch relative to the control medium. None of the cell line-conditioned Grace's media had a significant effect on eggs attaining germ band stage compared with the Grace's control medium. However, Grace's medium conditioned with the IAL-TND1 and IPLB-LdFB cell lines promoted development beyond germ band, resulting in a significantly higher percentage of hatching eggs than the Grace's control medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiological bases for parasite-induced alterations of host behaviour

Parasitism is defined in various ways as an intimate relationship in which one partner, the parasite, lives on or in another, the host, generally at the expense of the latter. Parasitism commonly results in a unique array of host physiological responses and adaptations. Most studies of the physiological effects of parasitism have focused on the pathological consequence of infection and disease. While many physiological changes contribute to pathogenesis, it is now recognized that parasitic infections at sub-clinical levels also produce physiological effects that either ameliorate or may not contribute to the disease process. Moreover, these physiological changes are often manifested by altered host behaviour. Behavioural studies have enabled an ecological- and evolutionary-oriented evaluation of host responses. In this fashion, physiological effects may be assessed as to whether they affect fitness and confer benefit or harm to one or both of the symbionts involved. We briefly examine how these physiological responses, specifically neural, endocrine, neuromodulatory, and immunomodulatory components, may interact to modify host behaviors. We consider the adaptiveness of these responses and how the behavioural patterns elicited may simultaneously appear adaptive for the parasite as well as the host. In addition, we address how parasite-host physiological and behavioural interactions may be altered during the course of parasitism.