Evaluating the Role of Histone H2A Variants and Epigenetic Modification in the DNA Repair System of Bdelloid Rotifers

Abstract

Bdelloid rotifers are microscopic invertebrates with an extraordinary ability to repair DNA double strand breaks (DSBs) induced by high doses of ionizing radiation. This DNA repair mechanism, although not well understood, likely evolved to allow bdelloids to recover from desiccation-induced DSBs. Interestingly, bdelloids possess histone H2A variants that are distinct from canonical H2A in that the proteins have longer C-terminal tails than those of other eukaryotes. Extended C-terminal tails are prospective targets for post-translational modifications (PTMs), which might facilitate DNA repair. The objective of this project was to use gene expression studies and high-resolution mass spectrometry (HR-MS) to investigate the role of bdelloid-specific H2A variants during DNA repair. To induce DSBs, the bdelloid Adineta vaga was exposed to 280 Gray of ionizing radiation. Following irradiation, RNA was extracted at time intervals and used for quantitative real-time PCR. Genes encoding H2Abd2 and putative H2AX were upregulated following irradiation, while other histone genes (H2B, H3, H4) were unaffected. This implies an involvement for H2A variants in DNA repair. Following irradiation, histones were also purified and subjected to HR-MS to identify relative protein quantities and PTMs in irradiated and non-irradiated bdelloids. Five H2A variants were identified and several PTMs appear to be novel to bdelloids and are candidates for involvement in DNA repair. Identifying PTM combinations and comparing those to patterns in other eukaryotes will establish the histone code for bdelloids and begin to elucidate the role for these proteins in DNA repair. This work was supported by grants from the NCRR (5P20RR016460) & NIGMS (8P20GM103429) from the NIH.