Schistosoma mansoni is a member of a genus of platyhelminths whose members cause the disease schistosomiasis. Particularly prevalent in sub-Saharan Africa, it is thought to be directly responsible for approximately 5500 deaths per year, as well as contributing significantly to morbidity, being responsible for 3.3 million lost disability-adjusted life years. Schistosomes are dioecious and male and female worms find one another and pair in the blood vessels of the host’s liver. This sets in motion a unique feature of schistosome biology, the pairing-dependent sexual maturation of the female worms. Over the course of the next three weeks, the females fully develop their reproductive organs, especially ovaries and vitellarian tissue, to allow for the production of large quantities of eggs, which not only play a crucial role in the transmission of the parasites but are also responsible for much of the pathology associated with schistosomiasis.

This thesis aims to explore the changes in gene expression which take place following pairing and result in the sexual maturation of females. To do so, RNA-Seq data was produced from male and female worms from mixed sex as well as single sex infections at 18, 21, 28, 35, 38 and 49 days post infection and analysed to understand when and how gene expression changes in paired worms. Then gene expression was examined in worms that had been removed from their partner to examine the process of regression, where female worms lose much of their reproductive tissue. The last experiments describe examine gene expression in the testes and ovaries of schistosomes, to reveal differences between the gonads of worms from mixed and single sex infections and understand in more detail how these worms may regulate the growth of their reproductive organs, contributing to our knowledge of schistosome biology.