Abstract
Schistosoma mansoni is a parasite responsible for bilharzia. This neglected tropical disease has also been prevalent in Corsica since 2013. The life cycle of the parasite is divided between a mammalian host where it does it sexual reproduction and a freshwater snail host where it does clonal multiplication. Cercariae is the parasite form that infests the mammal. The cercariae shedding follows a 24-hour rhythm based on the water activity peak of the mammalian host. In order to enhance the understanding of schistosome transmission to the mammalian host, the work of this thesis focuses on the cercariae shedding rhythm of the diurnal and nocturnal chronotypes of Schistosoma mansoni. This study is transversal by studying the phenomenon of cercariae shedding rhythm from the phenotype (chronobiology, histology) to the genes involved (genetics, epigenetics and transcriptomics). Chronobiology approaches revealed that the cercariae shedding rhythm adapts to photoperiod inversion and disappears in the absence of day/night alternation (continuous light or darkness) without however ruling on the endogenous or exogenous nature of this rhythm. The histological approach revealed that, in the absence of day/night alternation, there is an accumulation of mature cercariae waiting inside the sporocysts and an arrest of cercariogenesis thus highlighting the sporocyst as another actor in the phenotype of the cercarial emission rhythm. At the molecular level, the combination of genetic (linkage mapping), epigenetic (ChIPmentation) and transcriptomic (RNA-seq) approaches showed that no canonical clock gene is involved. However, all three approaches identified genes involved in the phototransduction mechanism with rhodopsin as the photoreceptor.