Identifying epigenetic differences between Ixodes scapularis (black-legged tick) infected and uninfected with Borellia burgdorferi

Abstract

Borrelia burgdorferi, the causative agent of Lyme disease, has long been recognized to modulate physiological and behavioural changes in the host for the disease, Ixodes scapularis. However, the mechanism by which this bacterium modulates these changes remains unknown. There are 3 distinct epigenetic mechanisms, histone modification, non-coding RNA regulation and DNA methylation, each of which alter gene expression through chromatin modification rather than changes in the genetic code itself. Epigenetics in the I. scapularis is relatively understudied, with little to no current research on DNA methylation specifically. Presently, it is unknown if DNA methylation changes or remains the same in the presence of B. burgdorferi. Furthermore, epigenetics has yet to be explored as the possible cause for the physiological changes in Ixodes scapularis, in response to infection by B. burgdorferi. In this study, the DNA methylation status of the pericentromeric tandem repeats family, Ixodes scapularis Repeats (ISR), in Borrelia-infected and non-infected I. scapularis samples was investigated. This was done through performing methylated-DNA immunoprecipitation reactions on I. scapularis DNA extracts of either infection status. DNA methylation status was quantified through a qPCR analysis involving the immunoprecipitated DNA, and primers targeting each ISR region. Calculations found that when comparing the ISR2A, ISR2D and ISR3 regions, overall significantly more DNA methylation was measured in the Borrelia-infected samples (p = 0.0129, n=3). The same trend was observed when targeting the ISR2B and ISR2C regions (n=1). Additionally, the ISR regions were found to be differentially methylated, with the ISR2A (p = 0005838, n=3) and the ISR3 (p = 0000833, n=3) regions experiencing significantly more DNA methylation than the ISR2D region. The ISRC region was also found to be more heavily methylated than the ISR2B region (n=1). This study found novel evidence that DNA methylation in I. scapularis may be responsive and modulated by the presence of B. burgdorferi. Additionally, it was demonstrated that distinct genomic regions can differ in their epigenetic responsiveness, and that the ISR2A, ISR2C and ISR3 may act as epigenetic markers in this organism. These results provide the groundwork for future epigenetic studies of the I. scapularis in relation to B. burgdorferi.