Many organisms monitor the annual change in day-length, and use this information for seasonal timing of their developmental, physiological and behavioural response. The molecular mechanisms underlying this photoperiodic timing are largely unknown. The wasp, Nasonia vitripennis, is an emerging model organism that exhibits a strong photoperiodic response: short autumnal days experienced by females leads to the inductionof developmental arrest (diapause) in their progeny, allowing winter survival of the larvae. How do the females control the developmental trajectory of their offspring is unclear. Here, I took advantage of the available complete genome sequence of the wasp, and tested the role of epigenetics in the photoperiodic response. I used reduced representation bisulfite sequencing (RRBS) to profile DNA methylation in adult females subjected to different photoperiods, and identified substantial differential methylation at the single base level. I have also found that knocking-down DNAmethyltransferase (Dnmt1a, Dnmt3), or blocking DNA methylation pharmacologically, largely disrupts thephotoperiodic diapause response of the wasps. In another set of experiments, I assessed the prevalence of 5-hydroxy methyl cytosine (5hmC), which is an intermediate in DNA demethylation in mammals. The results show that 5hmC is present in Nasonia although in limited amount and suggests that 5hmC-dependent demethylation may be evolutionary conserved in invertebrates. The role of microRNA (miRNA) in the photoperiodic response was also tested. I experimentally validated 32 of the computationally predicted Nasonia miRNA and tested their expression levels by using stem-loop real-time PCR. I identified significant differential expression in a sub-set of miRNA, which was induced by the photoperiod. To my knowledge, this is the first example uncovering the role of epigenetics in photoperiodic timing in insects.
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