November 17, 2009, 4PM - HSB T-639

2009 marks not only the 200th anniversary of Darwin's birth but also publication of the first evolutionary theory, Lamarck's Philosophie Zoologique. RNA, normally thought of as a conduit in gene expression, displays a novel mode of action in ciliates, where RNA molecules provide both an organizing role in DNA rearrangements and a template that can transmit somatic substitutions to the next generation (Nowacki et al. 2008. Nature 451, 153-158). The opportunity for RNA-guided DNA repair is profound in Oxytricha, which destroys 95% of its germline genome through a process that severely fragments its chromosomes and then sorts and reorders the hundreds of thousands of tiny pieces remaining. Information for reordering comes from transiently-expressed maternal non-coding RNAs. A complete RNA cache of the maternal somatic genome may be available at a specific stage during development to provide a template for DNA rearrangement and transmit heritable information. Furthermore, the occasional transfer of point mutations from these RNA templates to the rearranged molecules supplies a viable mechanism for stable inheritance of acquired characters (in either DNA sequence or alternative splicing pattern) without altering the germline. This mechanism for inheritance beyond the conventional DNA genome can pass information across multiple generations, hinting at the power of RNA molecules to reshape genome information.