Cell death and reproductive regression in female Schistosoma mansoni

The vitellarium is a highly proliferative organ, producing cells which are incorporated along with a fertilized ovum into the schistosome egg. Vitellarial growth fails to occur in virgin female schistosomes in single sex (female-only) infections, and involution of this tissue, which is accompanied by physical shrinkage of the entire worm, occurs when mature females sexually regress upon removal from their male partners. We have found that upon removal from their hosts into tissue culture, female parasites regress whether they are mated or not, but that cessation of egg production and a decline in expression of the vitelline gene p14 is delayed by mating. We used BrdU labeling to investigate whether there was a loss of proliferation in the vittelarium that might account for regression and found that the proliferation rate declined equally in paired and singled females once placed into culture. However, TUNEL staining and Caspase 3 activity measurements indicate that the loss of vitrellarial cellularity associated with regression is associated with profound apoptotic vitelline cell death, which is not apparent in the vitellaria of paired females immediately ex vivo, and which develops in vitro regardless of whether males are present or not. Furthermore, primordial vitellaria in virgin females have a high frequency of apoptotic cells but are characterized by a proliferation rate that is indistinguishable from that in fully developed vitellaria in mature paired females. Taken together, our data suggest that the vitelline proliferation rate is independent of pairing status. In contrast, the survival of vitelline cells, and therefore the development of the vitellarium, is highly male-dependent. Both processes are negatively affected by removal from the host regardless of whether male worms are present or not, and are unsustainable using standard tissue culture approaches.     

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.     

Tyrosine kinase and cooperative TGFbeta signaling in the reproductive organs of Schistosoma mansoni

Drug-induced suppression of female schistosome sexual maturation is an auspicious strategy to combat schistosomiasis since the eggs are the causative agent. The establishment of drug targets requires knowledge about the molecular mechanisms that regulate the development of the female reproductive organs, which include vitellarium and ovary. This review summarizes recent studies suggesting tyrosine kinases as important factors for the regulation of female gonad development. In this context, especially cytoplasmatic tyrosine kinases of the Src class seem to play dominant roles. Moreover, experimental data and theoretical concepts are provided supporting a crosstalk between tyrosine kinase and TGFbeta signaling in the production of vitellocytes. Finally, we take advantage from the schistosome genome project to propose a model for the regulation of vitelline-cell production and differentiation.     

Schistosoma mansoni: Astiban-induced damage to tegument and the male reproductive system

Astiban produced structural damage in male Schistosoma mansoni (Puerto Rican strain) in mice. The degree of disorganization was directly related to the dosage administered, although initial changes in structure for the first three doses (3 × 30–40 mg/kg) varied between individual worms of the same infection. More consistent damage to the tegument, parenchyma, and reproductive organs occurred after 6 × 40 mg/kg of Astiban injections. Exposure of the subtegumentary musculature preceded appearance of an increased number of noncytoplasmic spaces in various tissues, probably a result of osmotic stress. Testicular disorganization was prominent initially in spermatozoa and spermatids, but became more generalized with drug accumulation. The sustentacular cells showed increased phagocytic activity with testicular damage. Continuous administration of drug resulted in a general distortion of the worm's morphology. However, partial recovery occurred within 22 days following cessation of drug administration.     

Stability and reproductive fitness of Schistosoma mansoni isolates with decreased sensitivity to praziquantel.

These studies are focused on schistosomes derived from human infections not cured by three successive doses of praziquantel that also produced infections in mice that were significantly more difficult to cure than infections with control worms. Half (three of six) of these isolates retained their decreased response to praziquantel after multiple passages through the life-cycle in the absence of therapeutic pressure. Two of the isolates, including the one initially least sensitive to praziquantel; reverted, to a sensitivity not significantly different from controls. For example, the EE6 isolate initially required 680 mg/kg praziquantel to affect a 50% reduction in worm load in murine infections, but after only six passages through the life cycle over 5 years this was reduced to 113 mg/kg, not different from control infections. The stability of some of the isolates and the reversion of others indicates that the biological or genetic factors conferring decreased praziquantel response varies among the isolates. The three isolates that retained decreased sensitivity to praziquantel all showed compromises in reproductive fitness in the laboratory, expressed most frequently as a decreased cercarial production from snails infected with those isolates compared to controls. For example, the total cercarial production of snails infected with the EE10 isolate was only 57% that of controls. The reversion of some of the isolates to a praziquantel sensitive state and the decreased reproductive fitness of those that did not revert suggest that there is some biological cost associated with the relative praziquantel insensitivity of these worms, which could help limit the impact of such isolates in the field. Infections with the less sensitive isolates also produced significantly less circulating schistosomal antigen in mice, suggesting that a decrease in the host immune response elicited by these worms could be one of the factors contributing to the diminished praziquantel efficacy.     

Catecholamine-containing neurons in Schistosoma mansoni

Summary Falck's method for the demonstration of monoamines was applied to the flatworm Schistosoma mansoni. Whole mount preparations and sections of frozen dried specimens showed that a primary catecholamine is present in four pairs of large nerve cells and in two longitudinal fiber tracts showing varicosities. Smaller neurons were found along these tracts. They are united by commissures and give off many branches which end in small dilatations.Contribution number 14 from the Schistosomiasis Research Unit, Institute of Biological Sciences, Federal University of Minas Gerais, Brazil. This study has been supported by research grants from the U.S. Army (DAAC 19-70-G-0023 and DAHG-70-G-0028), CAPES and Conselho Nacional de Pesquisas, Brazil. For technical assistance we thank Mr. Rubens Miranda, technician supported by the Conselho Nacional de Pesquisas of Brazil.     

Fucosyltransferases in Schistosoma mansoni development

Glycoconjugate-bound fucose, abundant in the parasite Schistosoma mansoni, has been found in the form of Fucalpha1,3GlcNAc, Fucalpha1,2Fuc, Fucalpha1,6GlcNAc, and perhaps Fucalpha1,4GlcNAc linkages. Here we quantify fucosyltransferase activities in three developmental stages of S. mansoni. Assays were performed using fluorophore-assisted carbohydrate electrophoresis with detection of radioactive fucose incorporation from GDP-[(14)C]-fucose into structurally defined acceptors. The total fucosyltransferase-specific activity in egg extracts was 50-fold higher than that in the other life stages tested (cercaria and adult worms). A fucosyltransferase was detected that transferred fucose to type-2 oligosaccharides (Galbeta1,4GlcNAc-R), both sialylated (with the sialic acid attached to the terminal Gal by alpha2,3 or 2,6 linkage) and nonsialylated. Another fucosyltransferase was identified that transferred fucose to lactose-based and type-2 fucosylated oligosaccharides, such as LNFIII (Galbeta1,4(Fucalpha1,3)GlcNAcbeta1,3Galbeta1,4Glc). A low level of fucosyltransferase that transfers fucose to no-sialylated type-1 oligosaccharides (Galbeta1,3GlcNAc-R) was also detected. These studies revealed multifucosylated products of the reactions. In addition, the effects of fucose-type iminosugars inhibitors were tested on schistosome fucosyltransferases. A new fucose-type 1-N-iminosugar was four- to sixfold more potent as an inhibitor of schistosome fucosyltransferases in vitro than was deoxyfuconojirimycin. In vivo, this novel 1-iminosugar blocked the expression of a fucosylated epitope (mAb 128C3/3 antigen) that is associated with the pathogenesis of schistosomiasis.     

Schistosoma mansoni and Schistosoma japonicum: Utilization of amino acids

, , and 1972. Schistosoma mansoni and Schistosoma japonicum: utilization of amino acids. International Journal for Parasitology 2: 425–430. The production of ¹⁴CO₂ from 12 labeled amino acids by S. mansoni and S. japonicum was studied. No ¹⁴CO₂ was detected from incubations with glycine, isoleucine, leucine, lysine or phenylalanine. Differences were found between sexes and/or species for the other amino acids studied. Species related differences included a greater rate of metabolism of glutamic and aspartic acid by S. mansoni than by S. japonicum. Proline and histidine were utilized by S. mansoni males and females, respectively. S. japonicum male worms did not utilize proline, while histidine was not utilized by the female of this species. Major sex related differences included greater ¹⁴CO₂ production from glutamic acid, aspartic acid and arginine by S. mansoni males than by females, and the utilization of histidine by male S. japonicum but not by females. Incubation in tyrosine resulted in the release of only small amounts of ¹⁴CO₂ by female worms of both species but no ¹⁴CO₂ production by male worms.     

Underestimation of Schistosoma mansoni prevalences

Field methods used for detecting Schistosoma mansoni infection miss a certain proportion of the infections. Prevalences of infection appear to be far under-estimated by faecal screening, with important consequences for control and research. Sake de Vlos and Bruno Gryseels investigate how the number of undetected infections can be statistically inferred from population surveys.