Poster abstracts
Poster number 9 submitted by Meredith Sigman
The transposable element’s Achilles’ heel: Do double-strand breaks trigger recognition and epigenetic silencing?
Meredith J. Sigman (Molecular Genetics, OSU), R. Keith Slotkin (Molecular Genetics, OSU)
Abstract:
Transposable elements (TEs) are mobile fragments of DNA that cause double-stranded DNA breaks upon transposition and are thus inherently mutagenic. To prevent DNA damage, multicellular organisms such as the model plant Arabidopsis thaliana transcriptionally silence TEs via heterochromatin formation enacted through epigenetic modifications such as DNA and histone methylation. Cytosine methylation is added to a TE locus through a small RNA-guided pathway termed RNA-directed DNA Methylation (RdDM). It has been previously demonstrated that RNA Polymerase V, a plant specific polymerase derived from Pol II, plays a role in DNA double-stranded break repair (1), but thus far, it is unknown whether this involvement can trigger methylation around break site. The dual role of POL V as well as other canonical RdDM proteins in double-stranded break repair begs the question of whether this pathway can also serve as a preliminary surveillance mechanism capable of targeting TE and exogenous DNA at the genome integration step. I hypothesize that the cell uses the double-strand break that the TE creates upon transposition to target DNA methylation (and hence epigenetic silencing) to a TE locus as soon as it duplicates. This study utilizes CRISPR-Cas9 mediated double-stranded breaks to assay whether a double-stranded break is sufficient to recruit proteins involved RdDM and trigger cytosine methylation. Preliminary evidence shows low level CHH methylation at a previously unmethylated region near the break site in wildtype plants. In addition to furthering the understanding of RdDM and DNA silencing, this project has broader impacts: If a double stranded break alone is sufficient to initiate DNA methylation, many researchers employing CRISPR may be drawing less that accurate conclusions due to regional epigenetic alterations around a targeted break.
References:
1. Wei, W. et al. A role for small RNAs in DNA double-strand break repair. Cell 149, 101–12 (2012)
Keywords: DNA Methylation, Double-stranded break, Epigenetic