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Seminar series on The Evolution of Genomic Architecture - Laura Landweber: RNA-mediated Genome Rearrangement in the Ciliate Oxytricha

  • Date: Feb 28, 2019
  • Time: 11:00 - 12:00
  • Speaker: Laura Landweber from Columbia University in New York, USA
  • Her you find more information on the speaker: https://biology.columbia.edu/people/landweber
  • Location: MPI Plön
  • Room: Lecture hall
  • Host: Jenna Gallie & Julien Dutheil

Abstract:

The ciliate Oxytricha trifallax possesses a dynamic pair of genomes, and massive DNA rearrangements produce a highly fragmented but functional somatic macronucleus from a complex germline micronucleus. This process eliminates nearly all noncoding DNA, including transposons, and rearranges over 225,000 short DNA segments to produce a second genome containing thousands of gene-sized "nanochromosomes." In the precursor, germline genome, the shattered segments of different genes often interweave with each other, frequently overlap and sometimes combinatorially assemble (Chen et al. 2014 Cell 158:1187). The mature, somatic genome contains over 16,000 nanochromosomes (Swart et al., 2013 PLoS Biology 11: e1001473). Noncoding RNAs regulate the entire process of genome rearrangement. Millions of 27nt piRNAs provide the critical information to mark and protect the retained DNA segments of the genome (Fang et al., 2012 Cell 151:1243) and a distinct set of piRNAs mark a subset of deleted regions to assist with their elimination. Maternally-inherited, long, non-coding (lnc) RNAs provide three additional layers of continuity across generations, including serving as templates for genome remodeling and RNA-guided DNA repair (Nowacki et al., 2008 Nature 451:153) while also regulating gene dosage and chromosome copy number (Nowacki et al., 2010 PNAS 107:22140). This illustrates the ability of noncodingRNAs to transmit heritable changes to the next generation. Together, Oxytricha's elaborate epigenome, assembled through complex interacting networks of both long and small non-coding RNAs, encapsulates an RNA-driven world, packaged in a modern cell.

 
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