Book of Abstracts: Albany 2009
June 16-20 2009
© Adenine Press (2008)
RNA-mediated Epigenetic Mechanism of Genome Rearrangement
RNA, normally thought of as a conduit in gene expression, has a novel mode of action in ciliates, where maternal RNA templates provide both an organizing guide for DNA rearrangements and a template that can transmit spontaneous point substitutions that may arise during somatic growth to the next generation (Nowacki et al. Nature 451, 153-158 (2008)). This opportunity for RNA-guided DNA repair is profound in its regulation of global DNA rearrangements in Oxytricha, involving loss of 95% of its germline genome, through a process that severely fragments its chromosomes and then sorts and reorders the hundreds of thousands of pieces remaining. Information for reordering comes from transiently-expressed maternal RNAs. A complete RNA cache of the maternal somatic genome may be available at a specific stage during development to provide a template for correct and precise DNA rearrangement. Furthermore, the occasional transfer of point mutations in these RNA templates to the rearranged molecules provides a mechanism for stable inheritance of acquired, spontaneous somatic mutations (in either DNA sequence or alternative splicing pattern) without altering the germline genome. This mechanism for inheritance beyond the conventional DNA genome can epigenetically transfer information across multiple generations, hinting at the power of RNA molecules to shape genome information. The evolutionary consequences of a viable mechanism in ciliates to transmit acquired characters may contribute to their cosmopolitan success, as well as high substitution rates in somatic sequence comparisons.
1Department of Ecology and Evolutionary Biology