Abstract
Schistosomiasis affects more than 200 million people globally. The pathology of schistosome infections is due to chronic tissue inflammation and damage from immune generated granulomas surrounding parasite eggs trapped in host tissues. Schistosoma species are unique among trematode parasites because they are dioecious; females require paring with male parasites in order to attain reproductive maturity and produce viable eggs. Ex vivo cultured females lose the ability to produce viable eggs due to an involution of the vitellarium and loss of mature oocytes. In order to better understand schistosome reproductive biology we used data generated by serial analysis of gene expression (SAGE) to identify uncharacterized genes which have different transcript abundance in mature females, those that have been paired with males, and immature females obtained from unisexual infections. To characterize these genes we used bioinformatics, transcript localization, and transcriptional analysis during the regression of in vitro cultured females. Genes transcribed exclusively in mature females localize primarily in the vitellocytes and/or the ovary. Genes transcribed exclusively in females from single sex infections localize to vitellocytes and subtegumental cells. As female reproductive tissues regress, eggshell precursor proteins and genes involved in eggshell synthesis largely have decreased transcript abundance. However, some genes with elevated transcript abundance in mature adults have increased gene expression following regression indicating that the genes in this study function both in eggshell biology as well as vitellogenesis and maintenance of female reproductive tissues. In addition, we found that genes enriched in females from single sex infections have increased expression during regression in ex vivo females. By using these transcriptional analyses we can direct research to examine the areas of female biology that are both relevant to understanding the overall process of female development and worm pairing while determining novel therapeutic approaches directed at the maturation of female schistosomes.
Highlights
Schistosomiasis, caused by infections with trematode parasites from the genus Schistosoma, affects more than 200 million people worldwide [1]
We found that the genes with higher transcript abundance in sexually mature female worms were expressed in female reproductive tissues, while those transcripts enriched in sexually immature worms were present in sub-surface somatic cells
Gene identification Nineteen transcripts that were found by serial analysis of gene expression (SAGE) to be present at higher levels in AFMS and two with higher transcript abundance in AFSS were chosen for further analysis
Summary
Schistosomiasis, caused by infections with trematode parasites from the genus Schistosoma, affects more than 200 million people worldwide [1]. Schistosomula migrate first to the lungs and to the liver sinusoids. In the liver juvenile parasites begin blood feeding and pair prior to migrating to the mesenteric or rectal veins (S. mansoni and S. japonicum) or to the perivesical venous plexus of the bladder (S. hematobium) where they mature into adult parasites. Paired worms produce eggs that pass out of the host in the urine or feces. These eggs can become trapped in immune-generated granulomas in host tissues, primarily the liver, bladder wall and intestinal epithelium, causing a strong Th2 immune response resulting in the pathology associated with schistosomiasis. Since eggs are central to the pathology of schistosomiasis and the transmission of the parasite to the intermediate host it is essential to improve our understanding of worm reproductive biology
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