The Epigenetic Effect of Trematode Infection on the Snail Host Zeacumantus subcarinatus
Parasites are able to modify their host’s morphology and physiology to increase their own fitness and transmission success; this phenomenon is known as parasite-induced host manipulation (PIHM). Though PIHM is widely observed in many lineages, the exact mechanism by which parasites elicit these effects is yet to be determined. However, parasites may induce these host modifications by causing changes at the DNA level by causing epigenetic changes. Epigenetics encompasses environmentally-induced heritable changes in the phenotype through changes in gene expression patterns without the primary nucleotide sequence being altered. The changes in gene expression occur due modifications at both the DNA and histone level which act to either activate or silence gene expression; various hypotheses exist about the mechanisms behind these changes in gene expression. These epigenetic changes often lead to dramatic biological outcomes due to their important roles as gene regulators. Given that parasitic infection is a major environmental factor on the host, and epigenetic changes are highly reactive to such environmental factors, it is very plausible that parasites may be exploiting this system to induce the PIHM phenotypes observed. Thus, the current study investigated whether epigenetic differences were present in the mud snail Zeacumantus subcarinatus when infected with the trematodes Philophthalmus sp. and Maritrema novaezealandensis compared to uninfected conspecifics. Differences in epigenetic modifications between infected and uninfected snails were investigated at both the DNA and histone level using enzyme-linked immunosorbent assay (ELISA) to determine global DNA methylation levels and mass spectrometry (MS) to determine the patterns of histone modification in infected versus uninfected individuals. No significant differences in mean 5-methylcytosine levels were detected between uninfected Z. subcarinatus snails and those infected with either Philophthalmus sp. or M. novaezealandensis. Similarly, no overall differences were found in the pattern of global histone post-translational modifications between uninfected Z. subcarinatus snails and those infected with either Philophthalmus sp. or M. novaezealandensis. Therefore, the current study determined that parasitic infection does not broadly affect host epigenetics. These findings fit with the current knowledge in the field which finds that epigenetic changes on such broad levels often lead to disease, as these epigenetic marks are important gene regulators. Any parasite-induced epigenetic changes in their host are likely to be targeted at the level of DNA methylation patterning and changes at the individual quantity of each histone PTM, which are known to exert strong biological effects, therefore future studies should be focused at such a level.
Advisor: Poulin, Robert; Dearden, Peter
Degree Name: Master of Science
Degree Discipline: Zoology
Publisher: University of Otago
Keywords: snails; epigenetics; parasite; host-parasite
Research Type: Thesis