The subcellular localization of labelled tyrosine in the vitelline cells of Schistosoma mansoni

Exploring Structural and Physical Properties of Schistosome Eggs: Potential Pathways for Novel Diagnostics?

In this era of increasing demand for sensitive techniques to diagnose schistosomiasis, there is a need for an increased focus on the properties of the parasite eggs. The eggs are not only directly linked to the morbidity of chronic infection but are also potential key targets for accurate diagnostics. Eggs were the primary target of diagnostic tools in the past and we argue they could be the target of highly sensitive tools in the future if we focus on characteristics of their structure and shell surface that could be exploited for enhanced detection. In this review, we discuss the current state of knowledge of the physical structures of schistosome eggs and eggshells with a view to identifying pathways to a comprehensive understanding of their role in the host-parasite relationship and pathogenesis of infection, and pathways to new strategies for development of diagnostics.

Structural and metabolic changes in femaleSchistosoma mansoni following male stimulation

Pairing of males and females from single-sex infections results in the multiplication and differentiation of undifferentiated cells of the vitelline lobule culminating in the production of mature vitelline cells involved in egg shell formation. These changes are accompanied by increases in the rate of uptake of tyrosine, thymidine, and an increased accumulation of calcium.

Schistosoma mansoni: the egg, biosynthesis of the shell and interaction with the host

The schistosome eggshell is a hardened and tanned structure made from cross-linked proteins. It is synthesized within the female worm from many different kinds of proteins and glycoproteins. Once the egg is released in the circulation, the outer surface of the eggshell is exposed and hence a direct site of interaction between the parasite and the host. The major eggshell protein is p14, but about one third of the eggshell is made from common cellular proteins, some of which are known to be immunogenic. This has many consequences for parasite-host interactions. However, so far, the eggshell has gained little attention from researchers. We will discuss the structure of the eggshell and its role in granuloma formation, host factor binding and egg excretion.

Schistosoma mansoni: changes in the rate of tyrosine uptake by unisexual females after stimulation by males and male extracts

The rate of uptake of H3 tyrosine by unisexual females in vitro was accelerated by 22% when male worm extract was added to the culture medium. Pairing of unisexual females with mature male worms in vitro resulted in a similar acceleration of H3 tyrosine uptake. As tyrosine is avidly taken up by the vitelline gland for the formation of egg shell protein the change in the rate of H3 tyrosine uptake can be employed as a sensitive quantitative criterion for assessing its development following stimulation.

The embryonic development of Schistosoma mansoni eggs: proposal for a new staging system

Schistosomiasis is a water-borne parasitic illness caused by neoophoran trematodes of the genus Schistosoma. Using classical histological techniques and whole-mount preparations, the present work describes the embryonic development of Schistosoma mansoni eggs in the murine host and compares it with eggs maintained under in vitro conditions. Two pre-embryonic stages occur inside the female worm: the prezygotic stage is characterized by the release of mature oocytes from the female ovary until its fertilization. The zygotic stage encompasses the migration of the zygote through the ootype, where the eggshell is formed, to the uterus. Fully formed eggs are laid still undeveloped, without having suffered any cleavage. In the outside environment, eight embryonic stages can be defined: stage 1 refers to early cleavages and the beginning of yolk fusion. Stage 2 represents late cleavage, with the formation of a stereoblastula and the onset of outer envelope differentiation. Stage 3 is defined by the elongation of the embryonic primordium and the onset of inner envelope formation. At stage 4, the first organ primordia arise. During stages 5 to 7, tissue and organ differentiation occurs (neural mass, epidermis, terebratorium, musculature, and miracidial glands). Stage 7 is characterized by the nuclear condensation of neurons of the central neural mass. Stage 8 refers to the fully formed larva, presenting muscular contraction, cilia, and flame-cell beating. This staging system was compared to a previous classification and could underlie further studies on egg histoproteomics (morphological localizome). The differentiation of embryonic structures and their probable roles in granulomatogenesis are discussed herein.

Identification of Schistosoma mansoni gender-associated gene transcripts by cDNA microarray profiling

BACKGROUND

Parasitic helminths of the genus Schistosoma mate, achieve sexual maturity and produce eggs in the bloodstream of their definitive hosts, and the most important pathological consequences of the infection are associated with this process. We have used cDNA microarray technology to initiate genome-wide gene-expression studies of sex and sexual development in mature Schistosoma mansoni parasites.

RESULTS

An S. mansoni-specific cDNA microarray was fabricated using 576 expressed sequence tags selected from three cDNA libraries and originating from two different parasite developmental stages. Five independent cDNA microarray hybridizations were analyzed using stringent filtering criteria and careful quality control, leading to the identification of 12 new female-associated and 4 new male-associated gene transcripts in the mature adult schistosome. Statistical analysis of variation demonstrated high levels of agreement within a cDNA microarray (correlation coefficient 0.91; median coefficient of variation 11.1%) and between cDNA microarrays (correlation coefficient 0.90; median coefficient of variation 14.4%). RT-PCR analysis confirmed the cDNA microarray results, thereby supporting the reliability of the system.

CONCLUSIONS

Our study expands the list of S. mansoni gender-associated gene transcripts from all previous studies by a factor of two. Among the new associations identified, a tyrosinase ortholog was preferentially expressed in the adult female, and a dynein light-chain ortholog was highly induced in the adult male. cDNA microarrays offer the potential for exponential leaps in the understanding of parasite biology and this study shows how molecules involved in sexual biology can be rapidly identified.

Dolichol phosphate is a rate-limiting factor in mannosyl transferase activity of adult male worms of Schistosoma mansoni

The formation of mannolipid through catalysis by mannosyl transferase of adult females of Schistosoma mansoni was found to be 2-3-fold higher than male worms. In contrast, mannosyl transferase in immature females generated approximately the same amount of mannolipid as male worms, immature or not. Exogenous dolichol phosphate added to homogenates of male worms produced a stoichiometric increase in mannolipid formation. Saturating amounts of dolichol phosphate generated similar mannosyl transferase activities in male and female homogenates, showing that in S. mansoni, dolichol phosphate is the lipid intermediate in the glycosylation reaction and that this mannolipid is a rate-limiting substrate. Thin layer chromatography revealed that the mannolipid was identical in male and female worms. Adult males incubated with 14C-acetate synthesised several apolar compounds, one of which displayed a Rf identical to that of the mannolipid. When exposed to 14C-acetate treated males in vitro, untreated females were able to incorporate a compound, which partitioned in the same way as the mannolipid. The increased mannosyl transferase-dependent mannolipid formation in adult females may reflect a higher energy demand by these parasites, which is probably associated with oogenesis.

Schistosoma mansoni: females enhance [14C]-tyrosine incorporation in males maintained in vitro

Incorporation of radiolabelled tyrosine was examined in males of Schistosoma mansoni maintained in vitro. Adult worms were recovered from mice and only those that were paired were used. Males and females were separated and placed in 4 degrees C RPMI 1640 containing 10% fetal calf serum (FCS). Individual males were incubated for 1 h either alone or with a female. Other males were incubated in a medium containing 40 ng ml-1 recombinant tumour necrosis factor alpha (rTNF alpha). Subsequently, males were incubated with or without females for 1 h in a medium containing 20 muCi ml-1 [14C]-tyrosine. All incubations were carried out in RPMI 1640 containing 10% FCS at 37 degrees C under 5% CO2. Untreated single males incorporated small amounts of labelled tyrosine. Pretreatment of single males with rTNF alpha did not affect their tyrosine incorporation (P = 0.693). However, males maintained in vitro with females incorporated 221% more tyrosine than the controls (P = 0.00008), suggesting that a chemical stimulus from the female affects tyrosine incorporation in males.

Sex determination and female reproductive development in the genus Schistosoma: a review

Parasites of the genus Schistosoma were among the first metazoans to develop separate sexes, which is chromosomally determined in the fertilized egg. Despite the occurrence of specific sex chromosomes, the females of most Schistosomatidae species do not complete their somatic development and reach no sexual maturity without the presence of males. Indeed, the most controversial and at the same time most fascinating aspect about the sexual development of Schistosoma females lies on discover the nature of the stimulus produced by males that triggers and controls this process. Although the nature of the stimulus (physical or chemical) is a source of controversy, there is agreement that mating is a necessary requirement for maturation to occur and for migration of the female to a definitive final site of residence in the vascular system of the vertebrate host. It has also been proposed that the stimulus is not species-specific and, in some cases, not even genus-specific. Despite a vast literature on the subject, the process or processes underlying the meeting of males and females in the circulatory system have not been determined and as yet no consensus exists about the nature of the stimulus that triggers and maintains female development. In the studies about their role, Schistosoma males have been considered, at times pejoratively, the brother, the muscles or even the liver of females. Indeed, it still remains to be determined whether the stimulus responsible for female maturation involves the transfer of hormones, nutrients, neuromediators, mere tactile stimulation or a combination of chemotactic and thigmotactic factors.

Schistosoma mansoni: effect of recombinant tumor necrosis factor alpha on fecundity and [14C]-tyrosine uptake in females maintained in vitro

It has been reported that recombinant tumor necrosis factor alpha (rTNF alpha) stimulates egg-laying in Schistosoma mansoni females. Because tyrosine requirement is increased in female undergoing sexual maturation in preparation for oogenesis and tyrosine is a major component of eggshell protein, we wanted to determine whether females treated with rTNF alpha would also incorporate more tyrosine. Adult females were first treated with 10, 20 or 40 ng/ml rTNF alpha for 1, 3 or 6 hr in RPMI 1640 containing 10% fetal calf serum (FCS). Another two groups of females were each exposed either to males or to male excretory-secretory (ES) products for 1 hr. They were then exposed to 20 microCi/ml-1 [14C]-tyrosine for 1 hr in RPMI 1640 containing 10% FCS. All females were incubated individually unless indicated otherwise. Females incorporated more tyrosine after exposure to males or their ES products. They incorporated significantly more tyrosine when treated with rTNF alpha for 1 hr; the increased uptake correlated with increasing amounts of rTNF alpha used. Although after a 3-hr treatment with 10 ng/ml rTNF alpha females incorporated slightly more tyrosine than controls, increasing amounts of rTNF alpha had an adverse effect. Females treated with rTNF alpha for 6 hr incorporated less tyrosine than controls and those treated for 1 hr. SDS-PAGE and fluorography did not reveal any differences in polypeptide profiles of untreated and rTNF alpha-treated females. These unexpected results led us to study the effect of rTNF alpha on fecundity in females. Contrary to the published report, we observed a sharp decline in egg-laying in females when exposed to increasing concentrations of rTNF alpha in vitro.

Electrophoretical and histochemical characterization of Schistosoma mansoni phenol oxidases

The phenol oxidase system, which is thought to play a central role in eggshell formation, was analyzed by means of electrophoretic and histochemical techniques. In contrast to current beliefs, our data show that males also express the phenol oxidase activity. The analysis of the electrophoretic pattern from males and females shows differences: adult males present a major band and a faint band, migrating slightly below. Adult females express a more complex pattern composed of four bands. Histochemical studies revealed that female phenol oxidase is concentrated in the vitelline cells, is inhibited by DDC, and this inhibition is correlated with disruption of female egg production. The present studies, in agreement with other reports, reveal that female phenol oxidase may be involved in sclerotization of the S. mansoni eggshell.

Incorporation of radiolabelled amino acids by adult Schistosoma japonicum: further characterization of a putative eggshell precursor protein

The synthesis patterns of female-specific proteins of Schistosoma japonicum were further investigated with particular reference to the 34 kDa putative eggshell precursor protein. Adult male and female worms of S. japonicum were metabolically labelled with 14C-tyrosine, 14C-glycine and 35S-methionine in vitro. The rates of amino acid incorporation for female worms were significantly higher than for males in all radiolabelling experiments. Labelled proteins were resolved by two-dimensional gel electrophoresis and visualized by fluorography. By using 14C-tyrosine and 14C-glycine, the 34 kDa female protein band resolved into three major spots with pI 6.0, 5.8 and 5.6. On the other hand, labelling studies using 35S-methionine failed to reveal synthesis of any corresponding spots at Mr 34 kDa. These results, together with the observations that eggshell hydrolysates are very rich in glycine but poor in methionine, suggested that the 34 kDa putative eggshell precursor protein of S. japonicum consists of at least three isoelectric forms. In addition, we have demonstrated several other female-specific polypeptides synthesized by this worm.

Identification of a putative eggshell precursor protein of the female Schistosoma japonicum

In adult worms of Schistosoma japonicum, a prominent radiolabelled female-specific protein (34 kDa) was demonstrated on fluorography of SDS gels with the pulse incorporation of 14C-tyrosine in vitro, though it was difficult to detect major female-specific proteins by direct staining methods. This female-specific protein was demonstrated to localize exclusively in the vitelline cells by indirect immunofluorescence using the rabbit anti-34 kDa female protein antiserum. It was shown that 14C-tyrosine was selectively incorporated into the vitelline cells by the pulse labelled autoradiographs. Two days after the exposure of worms to radio-tyrosine, the shells of eggs in the uterus were demonstrated to have become radioactive, indicating that 14C-tyrosine-labelled protein was used as a material for the eggshell. In the fluorograph of proteins extracted from newly laid eggs in vitro, the prominent band was not found at the 34 kDa region, but a lot of radioactivity appeared at higher than 100 kDa. The results suggested that a 34 kDa female protein was a precursor of the eggshell and became a much larger protein molecule as a result of cross-linking during eggshell hardening.

Possible eggshell protein gene from Schistosoma mansoni

We have identified and sequenced a cDNA clone of a mRNA found only in mature female schistosomes. This mRNA is not detectably synthesized by female worms from single sex infections (unisexual females), by males or by the developing miracidia in the eggs. The clone hybridises to a highly abundant polyadenylated mRNA of approximately 1500 nucleotides. The nucleotide sequence of the clone predicts a polypeptide comprising two repetitive regions. A pentapeptide repeat with the consensus sequence Gly-Tyr-Asp-Lys-Tyr, and a region rich in histidine residues. Hybrid selected mRNA translated in vitro with [3H]tyrosine as labelled amino acid yields a polypeptide of 48 kDa (p48) that corresponds to the major [3H]tyrosine labelled translation product of female worm total mRNA. p48 does not label with [35S]methionine and is absent from the translation products of male and unisexual female mRNAs. The amino acid sequence of p48 has significant homologies to silk moth chorion proteins and we suggest that it is one of the major components of the schistosome eggshell probably accounting for the high level of [3H]tyrosine incorporation into the vitellaria of Schistosoma mansoni. The tyrosine content of the polypeptide suggests that it may play a role in phenol oxidase mediated cross-linking of the schistosome eggshell and in support of this we find that mushroom phenol oxidase will cause the specific cross-linking of p48 in in vitro translation products.

Estudo morfológico do Schistosoma mansoni Sambon, 1907 encontrado na espécie humana

O presente trabalho estuda; a morfologia do Schistosoma mansoni Sambon, 1907, obtido por filtração extra-corpórea de 5 (cinco) pacientes do Hospital São Vicente de Paula em Minas Gerais. Foram elucidados detalhes morfológicos até então controvertidos na literatura, tendo sido, inclusive, correlacionados com os estudados pela microscopia eletrônica por outros autores. Não foram observadas diferenças morfológicas entre os vermes humanos e os descritos em animais de pequeno porte.