The Department of Biomedicine
BBB seminar

BBB seminar: Daniel Chourrout

Area of genomic turbulence near vertebrates

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Daniel Chourrout
Sars International Centre for Marine Molecular Biology, University of Bergen

Tunicates are chordates, comprising also the subphylum vertebrata, but remained in the ocean. Initial phylogenetic analyses gave tunicates the basal position in the chordate tree, making many morphologists happy. It might indeed support a gradual increase of anatomical complexity during the evolution of chordates, up to the vertebrate summit. Tunicate phylogenetic position was made robust enough after we sequenced the genome of Oikopleura dioica, and this led us to opt for a somewhat different scenario. Tunicates would be the closest relatives of vertebrates and they would instead result from a secondary simplification.

Just a look at the new chordate tree and one can see extremely long branches on tunicates, reflecting a high long-term mutation rate. This is the subject of my presentation. Genome analysis showed plenty of other divergent features, including but not limited to genome compaction, loss of ancestral syntenies and the replacement of old introns. I will report on our recent efforts to figure out how such changes may have occurred, with focus on the modes of double strand break repair and intron processing. The perhaps most interesting overall question is whether rapid evolution is just an acceleration of universally conserved mechanisms or if it can make use of their very unusual modification.

Selected publications:

Henriet et al. (2019) Evolution of the U2 spliceosome for processing numerous and highly diverse non-canonical introns in the chordate Fritillaria borealis. Curr Biol 29, 3193-99

Deng et al. (2018) Prevalence of mutation-prone microhomology-mediated end joining in a chordate lacking the c-NHEJ DNA repair pathway. Curr Biol 28, 3337-41

Denoeud et al. (2010) Plasticity of animal genome architecture unmasked by rapid evolution of a pelagic tunicate. Science 330, 1381-5

Delsuc et al. (2006) Tunicates and not cephalochordates are the closest living relatives of vertebrates. Nature 439, 965-8

Seo et al. (2004) Hox cluster disintegration with persistent anteroposterior order of expression in Oikopleura dioica. Nature 431, 67-71


Chairperson: Mathias Ziegler, Department of Biomedicine