Tegumental glucose permeability in male and female Schistosoma mansoni

Tegumental hexose transporters have been kinetically characterized in mated and separated male and female Schistosoma mansoni 8-12 wk postinfection. Significant gender-specific differences in Km and Vmax were observed. In mated males, the estimated constants (mean +/- SE) were: Km = 0.63 +/- 0.31 mM, Vmax = 0.93 +/- 0.44 nmol/mg worm water/min, and the Kd = 0.25 +/- 0.09 microliter/mg worm water/min. In mated females the kinetics were: Km = 0.99 +/- 0.40 mM, Vmax = 1.22 +/- 0.42 nmol/mg worm water/min, and Kd = 0.60 +/- 0.14 microliter/mg worm water/min. The influx of 2-deoxy-D-glucose and 3-O-methylglucose has been similarly characterized; these analogs share the same glucose transporter in male and female schistosomes. 2-Deoxy-D-glucose has a higher affinity, and 3-O-methylglucose a lower affinity, than does glucose. Because mated male schistosomes supply glucose to female partners, similarities between the free glucose concentration of the male and the affinity of the transporter determined for mated female schistosomes suggest that male-to-female transfer may be a potentially rate-limiting step in glucose utilization by the female. Permeability x surface are (PS) products and Vmax/Km ratios were significantly elevated in mated schistosomes, suggesting that the transporter is primarily localized to the dorsal surface of the male. Gender- and mating-specific analyses of PS products indicate that tegumental permeability to glucose is significantly increased in mated schistosomes, and compares very favorably to that of the host liver.     

Dolichol phosphate mannose synthase is differentially expressed in male and female worms of Schistosoma mansoni

The cDNA encoding the Schistosoma mansoni dolichol phosphate mannose synthase was completely sequenced, displaying the highest homology with Cricetulus griseus and Saccharomyces pombe genes. The Schistosome enzyme had a K(m) of 0.127 microM, a value that is within the range of those reported for several other species. Thin-layer chromatography of the radiolabelled schistosome lipid intermediate showed it was identical to dolichol-phosphate (C80-C105). Expression of dolichol phosphate mannose synthase of S. mansoni (SmDPMS) was analysed by Northern blot and quantified by semi-quantitative RT-PCR with cDNA from mature and immature male and female worms. Northern blot analysis revealed a single 1-kb band. Both approaches confirmed a higher level of expression in mature female worms, as compared to immature and male worms.     

Schistosoma mansoni: a comparison of male and female muscle physiology

Surface electrical activity and membrane potentials recorded from male and female Schistosoma mansoni are similar. Surface electrical activity and responses to electrical stimulation are slightly higher in females. Contractures induced by praziquantel, 60 mM K+, ouabain or 5 degrees C are slightly less in females but responses to putative neurotransmitters (5-HT, dopamine and carbachol) are the same in both sexes. Females are more susceptible to the removal of Ca2+ and to the increase of Mg2+ in the medium. These differences may be due to anatomical differences in the sexes or to the recording methods used.     

Transintegumental uptake of metabolic substrates in male and female Schistosoma mansoni.

A new method for measuring transintegumental uptake in living schistosomes in vitro has been applied to the study of individual males and females. Uptake of a 14-C labeled test metabolite was compared to that of tritiated water (a highly diffusible reference substance). Use of the short half-life (T 1/2 = 100 min) isotope 113m-Indium, bound to EDTA (ethylene diamine tetra-acetic acid, a nondiffusible reference substance) permitted quantification of the relative amount of 14-C test substance passively adhering to the schistosoma surface. Substraction of this amount provided an estimate of net uptake. D-glucose uptake, as measured by this method, increased with time, approaching equilibrium by two min; a positive correlation between temperature and glucose uptake was also observed. Nondialyzable components in rat, human, horse and fetal calf sera did not enhance glucose uptake. In both male and female schistosomes, minimal uptakes were seen for the nonmetabolizable sugar alcohol mannitol (MW = 182). L-glucose uptake was similarly low, but high uptakes were observed in both sexes for D-glucose. In addition to confirming the stereospecificity of hexose uptake, these studies suggested our technique provides a sensitive method for measurement of both high and low uptake compounds. The uptakes of D-glucose and the L-amino acids--arginine, ornithine, lysine, histidine, phenylalanine and serine--were comparatively higher in female than male schistosomes. Slight elevations in uptake by females were observed for threonine, valine and glycine, but aspartate uptake was slightly higher in males. No dramatic male-female differences were immediately apparent for the uptakes of proline, leucine, isoleucine, tyrosine and glutamate. Schistosomal uptake of L-amino acids that are essential for vertebrates was generally higher than uptake of the nonessential amino acids.     

Schistosoma mansoni: influence of the female parasite on glutathione biosynthesis in the male

The glutathione (GSH) content of male Schistosoma mansoni increases in the absence of the female. This phenomenon, originally observed in vitro, also occurs within the host. At the time of recovery from mice, the GSH content of males from single-sex infections was 1.7-fold higher than that of paired males from mixed sex infections (P less than 0.01). The effect of mating status on male GSH biosynthetic and turnover rates was examined to determine the basis for increased GSH content in unpaired males. GSH turnover rates, measured when GSH biosynthesis was inhibited by greater than 95% with 5.0 mM DL-buthionine-SR-sulfoximine, were indistinguishable between unpaired and paired males with a first-order rate constant of 0.018 hr-1. In contrast, incorporation of L-[35S]cysteine into GSH revealed that GSH biosynthesis was 5-fold higher in unpaired than in paired males. Transport of L-cystine into male schistosomes, the presumed rate-limiting step in GSH biosynthesis, was unaffected by mating status. The GSH content increased when males were incubated in medium that had previously contained females or when separated from females by a microporous membrane. Males paired to 50% ethanol-fixed females had unchanged GSH content in vitro. It appears that male GSH biosynthesis may be regulated by a response stimulated by the female's physical presence in the gynechophoral canal and not by a soluble factor released from the female.     

Schistosoma mansoni: exposure in vitro of adult male surface antigens

Incubation of adult male Schistosoma mansoni for 24 hr in medium containing newborn calf serum or normal human plasma resulted in an increase in the amount of parasite antigen exposed at the worm surface. No effect was observed on the amount of host antigen which was present. The increase in the exposure of parasite antigens takes place progressively over 24 hr and is partially dependent on the presence of lipoproteins in the culture medium. The possibility is discussed that the increase is due to environmentally induced changes in surface membrane lipid composition.     

Homosexual male pairing in Schistosoma mansoni

and 1988. Homosexual male pairing in Schistosoma mansoni.International Journal for Parasitology 18: 1115–1117. To see whether male worms within the gynecophoral canal of another male worm would become feminized (i.e. express vestigial female-associated genes), we established homosexual pairs by twice exposing mice to male cercariae with a 4 or 6-week interval, and perfusing 3–5 weeks later. From 13 to 34% of these worms were found in pairs, compared with 0 to 7% in singly exposed controls. ‘Inner’ males in homosexual pairs showed no histological evidence of female reproductive structures, but were stunted, had poorly developed testes, and the high nuclear density characteristic of mature females. More vitelline follicles occurred in unpaired unisexual males than in homosexually paired males, fewest in bisexually paired males. Uptake of tyrosine, an indicator of vitelline development, occurred in the same relative order. The gynecophoral microenvironment often led to stunting, probably through starvation induced by the relative inaccessibility of host blood to homosexually clasped males.     

Effect of pairing in vitro on the glutathione level of male Schistosoma mansoni

The effect of in vitro incubation on the level of the intracellular nucleophile, glutathione (GSH), in adult Schistosoma mansoni was investigated. The GSH levels of freshly collected adult male and female parasites were 8.5 +/- 2.5 and 2.7 +/- 0.7 nmol/10 worms, respectively, as determined by an enzymatic assay. Twenty-four-hour incubation of unpaired males in RPMI-1640 medium at 37 C resulted in a 1.7-fold increase (P less than 0.001) in GSH level that remained elevated for at least 7 days. The increase was dependent on exogenous L-cystine, suggesting that it was due to biosynthesis of GSH. Biosynthesis in male S. mansoni was confirmed by isolating [3H] GSH from parasites incubated in medium containing L-[3H] cystine or [3H] glycine. In contrast to unpaired males, the GSH level of paired males as well as that of unpaired or paired females did not increase after 24 hr in vitro. When males that had been incubated unpaired for 24 hr were allowed to couple in vitro with freshly collected females, their GSH level fell to that of continuously paired males. These observations provide evidence that in vitro female schistosomes can influence the physiology of the male.     

Comparison between site-specific DNA binding proteins of male and female Schistosoma mansoni

Several amplicons with approximately 120 bp each, obtained from the upstream domain of Schistosoma mansoni female-specific gene F-10, were coupled to Dynabeads M-280 streptavidin. The beads were used as a matrix for affinity purification of nuclear proteins obtained from mixed populations of adult worms. A protein of approximately 12 kDa, bound to the DNA in a sequence-independent manner. In contrast, when the DNA matrix was narrowed down to smaller synthetic oligonucleotides, bearing sequences corresponding to the TATA box and the CAAT box, band-shift assays revealed that different nuclear proteins from either adult male or female worms formed complexes with the DNA adduct. In order to characterise the bound proteins, the same oligonucleotides were UV cross-linked to the male and female protein extracts. Whilst the band shift experiments showed that the proteins from each sex produced a distinct mobility pattern when the TATA box sequences were tested and a similar one when the CAAT box sequences were added to the proteins, UV cross-linking experiments revealed clear qualitative differences between both, male and female proteins and also between the proteins binding to the two motifs. These results are compatible with a model in which the differential expression of the F-10 gene might depend on individual sub-sets of proteins.     

Schistosoma mansoni: adult worm chemoattraction with barriers of specific molecular weight exclusions

Chemoattraction studies were done with Schistosoma mansoni adults from mice. To test for attraction or repulsion, some worm pairs were separated mechanically and the individuals placed in polycarbonate chambers. Experiments were done at 37 C and chambers contained dialysis tube chimneys. In all cases, heterosexual attraction occurred when one worm, but not two worms, were placed in the chimneys. Unperforated chimneys with specific molecular weight (Mr) exclusions were compared with perforated chimneys to study heterosexual attraction. Attraction was similar in designs using perforated chimneys and those with 50,000 and 12,000 Mr exclusions, but none was seen in chimney designs with 1000 Mr exclusions.     

Schistosoma mansoni: praziquantel-induced changes to the female reproductive system

The long-term in vivo effects of a single subcurative dose (200 mg/kg body wt of mouse) of praziquantel on the ultrastructure of the female reproductive system of Schistosoma mansoni were investigated. Morphological changes in the structure of both the vitelline gland and the ovary were apparent within 24 hr post-treatment, and lead to a partial or complete regression of both organ systems. Associated with this regression was a cessation of egg production. In surviving, paired females, irrespective of the initial severity of the drug-induced damage, both the vitelline gland and the ovary completely redeveloped and lead eventually to a resumption of egg production. In contrast, in unpaired, previously mature females the reproductive system also regressed but did not redevelop. In these cases, although the initial changes in the reproductive system were the result of drug action, the long-term regressive changes were due to discontinued male stimulation.     

Schistosoma japonicum is less sensitive to cyclosporin A in vivo than Schistosoma mansoni.

We compared the toxic effects of cyclosporin A (CsA) on postmigratory immature Schistosoma mansoni and Schistosoma japonicum in mice. For each species, CsA was administered either relatively early or late during development. Exposure of 20-day-old S. mansoni to 1 subcutaneous dose of CsA (50 mg/kg) reduced the worm burden by 45% and induced herniae and/or boli of the gut in 32% of perfusable worms. These results agree with previous reports. In addition, CsA induced a marked liver shift (37% of total worm number). For S. japonicum, CsA was administered at 11 days postinfection (PI) because this species migrates more quickly. Killing of worms and damage to the gut were not observed, and only a slight liver shift occurred. Similarly, these effects were not recorded when CsA was administered at the later times of 34 days PI for S. mansoni and 17 days PI for S. japonicum. For both species, CsA stunted worms, affecting both sexes early PI but only females late PI. In conclusion, immature worms of S. japonicum are less sensitive than S. mansoni to CsA. Also, S. mansoni displays marked age-dependent differences in its sensitivity to CsA.     

Schistosoma mansoni: nitrothiazolines and the male tegument

Within 24 hr of treatment of the mouse host with BW484C, 2-[5-nitro-2-(pivaloylimino)-4-thiazoline-3-yl]diacetamide, pairs of Schistosoma mansoni exhibited "hepatic shift" and began to leave the mesenteric veins. The tegument of the males was altered, both morphologically and physiologically, while that of females was unaffected. This morphological damage to males correlated well with therapeutic efficacy against both sexes in a range of analogues of BW484C. However, parasites removed from mice after treatment but before the hepatic shift and then maintained in vitro were far from moribund as treated males could be maintained for 8 days in vitro, although this was 5 days less than males from untreated mice. Females survived as well as control worms. In contrast, male and female S. mansoni remaining in their host after therapy were invaded by host cells in the liver after 2 days. The morphological effects and reduction of the in vitro survival of males treated in the mouse and removed after 24 hr could be simulated by in vitro exposure for 24 hr to 10(-5) M BW484C. Females were not susceptible to this regime. It was concluded that worm pairs were swept to the liver as a result of drug dependent damage to the tegument of the male and that phagocytic invasion of male and female schistosomes by host cells within the liver was an important factor in the efficacy of BW484C. The biochemical events underlying the effects on the tegument of male worms remain unknown.     

Schistosoma mansoni: activity responses in vitro to praziquantel.

The effects of praziquantel, a novel antischistosomal compound, on the activity of adult Schistosoma mansoni (Liverpool strain) in vitro were investigated. Worm activity was modified at all concentrations of praziquantel. High concentrations (above 0.5 microgram/ml) produced rapid paralysis, whilst low concentrations of praziquantel stimulated worm activity. It is concluded that such activity modification could lead to worm displacement in vivo.