Oral Presentation 41st Lorne Genome Conference 2020

L1 activity is a hallmark of cellular reprogramming in mammals (#25)

Sandra R Richardson (Mid-Career Award Winner) 1 , Patricia Gerdes 1 , Sue Mei Lim 2 3 4 , Adam Ewing 1 , Jose M Polo 2 3 4 , Geoffrey J Faulkner 1 5 6
  1. Mater Research Institute-University of Queensland, Woolloongabba, QLD, Australia
  2. Department of Anatomy & Developmental Biology, Monash University, Melbourne, VIC, Australia
  3. Development and Stem Cells Program, Monash Biomedicine Discovery Institute, Melbourne, VIC, Australia
  4. Australian Regenerative Medicine Institute, Monash University, Melbourne, VIC, Australia
  5. Queensland Brain Institute, University of Queensland, Brisbane, QLD, Australia
  6. Mater Medical Research Institute-University of Queensland, Woolloongabba, QLD, Australia

Long Interspersed Element 1 (LINE-1 or L1) retrotransposons are a major source of genome diversification and de novo mutagenesis in mammals1. Due to their copy-and-paste mode of mobilisation, L1 sequences occupy 17% and 18% of the human and mouse genomes, respectively, with ~100 active copies per human and ~3,000 active copies per mouse2,3,4,5. The accumulation of L1 sequences reflects an ongoing evolutionary conflict between the imperative for L1 to generate new heritable insertions, and the preservation of a stable germline genome. This conflict must play out in cells with the potential to contribute their genetic information to the next generation6. By analysing 3-generation mouse pedigrees with mouse retrotransposon-capture sequencing (mRC-seq), we found that most de novo L1 insertions can be traced to embryonic development, either in pluripotent cells of the early embryo, or in early primordial germ cells (PGCs)7. Thus, the extensive epigenetic reprogramming which characterises both of these niches may render the genome vulnerable to L1 mobilisation. Consistently, we also observe L1 mobilisation during cellular reprogramming in vitro. We applied RC-seq and whole-genome sequencing to 26 mouse induced pluripotent stem cell (miPSC) lines representing a panel of 9 parental cell types, as well as 18  single-cell miPSC clones derived from mouse embryonic fibroblasts, and uncovered a total of 41 reprogramming-associated L1 retrotransposition events. Our ongoing studies are aimed at characterising L1 regulation during cellular reprogramming, both globally and at the resolution of individual L1 copies, and understanding the consequences of reprogramming-associated L1 mutagenesis in vivo and in cultured cell models.

 

Mid-Career Award Sponsored by

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  1. Richardson, S. R. et al. Microbiology spectrum 3(2), (2015).
  2. Lander, E. S. et al. Nature 409, 860-921 (2001)
  3. Waterston, R. H. et al. Nature 420, 520-562 (2002)
  4. Brouha, B. et al. Proc Natl Acad Sci U S A 100, 5280-5285 (2003)
  5. Goodier, J. L. et al. Genome Res 11, 1677-1685 (2001).
  6. Richardson, S. R. & Faulkner, G. J. Bioessays 40, e1700189 (2018).
  7. Richardson, S. R. et al. Genome Res 27, 1395-1405 (2017).