Epigenetic factors affect the host:pathogen interaction between schistsoma mansoni and biomphalaria glabrata

Abstract

Schistosomiasis, also known as Bilharzia, is a neglected tropical disease (NTD) caused by the Schistosoma genus of trematode parasite and is estimated to affect 250 million people globally. The nucleus is a highly organised organelle with chromosomes and genes occupying distinct and reproducible locations. However, this spatial organisation is not fixed and different events such as differentiation, environmental stimuli, stress and replicative senescence can trigger genome reorganisation within nuclei. Previous work has already shown that when Schistosoma mansoni infects its obligate intermediate host Biomphalaria glabrata, a freshwater snail, it induces chromatin reorganisation resulting in subsequent upregulation of genes. B. glabrata genome organisation is more similar to mammalian than other invertebrates, meaning that there is potential for what can be discovered in the snail model to be applicable to the mechanism of infection in the human population. The mechanisms that are responsible for inducing gene movement or chromatin reorganisation are poorly understood, but hypothesised to be partly as a result of epigenetic signalling. Histone methyl modification patterning within the nuclei of B. glabrata were investigated following several events known to induce or result in chromatin reorganisation, heat-shock, infection and ageing. Following comparisons between controls and experimental groups several changes in pattern distribution were identified. Infection of B. glabrata by S. mansoni H3K79me3 showed significant alteration not replicated by heat-shock or ageing indicating that modification of H3K79me3 is an important target for the parasite infection. As such a protocol was developed to further investigate the visual co-localisation of gene and histone modification signals. To investigate the effects that potentially disrupting this induced chromatin reorganisation can cause, several drugs have been screened in the snail to assess their effect on subsequent changes in susceptibility. Susceptibility to infection was either assessed by one of two means. An absolute method scoring for complete resistance to infection. The second was counting the number of cercariae, the human infective stage of the Schistosoma lifecycle, that were shed from the snail. Drugs chosen were shown to either inhibit gene movement or target epigenetic factors that could be signalling for genome reorganisation to occur. Preliminary data have shown that affecting the acetylation within B. glabrata nuclei affects the snail’s susceptibility to S.mansoni infection. ii B. glabrata interphase genome organisation exhibits similarity to human nuclei, making it an excellent model organism for investigating the effects of genome reorganisation in vivo and as an invertebrate could be used to replace higher order models to reduce the use of animal models in research in line with the NC3R initatives. With a comparatively short lifespan of 12 months it is ideal for exploring, in vivo, ageing related changes to genome organisation. We have previously shown that gene movement and relocation to a new non-random location is possible within a short time period following a heat shock or an infection within juvenile snails. In 12 month aged snails it is demonstrated that significant genome reorganisation has occurred, with the heat shock protein 70kDa (hsp70) loci occupying a new non-random location within the nuclei and that neither heat-shock nor S. mansoni infection can induce gene relocation. Thus indicating not just significant changes to genome organisation but a potential loss of the mechanisms that are responsible for reorganisation of the chromatin. Using fluorescent imaging techniques, alterations to histone markers, protein distribution and gene loci positioning within nuclei were investigated at varying ages within B. glabrata. This verifies work done in human senescent cells in vitro replicating changes to genome organisation and chromobility. As such this work presents B. glabrata as a new model for investigating the effects of ageing on nuclear organisation in vivo.