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With Licence to Mutate

Loss of a DNA repair pathway in Oikopleura

This graph shows that in Oikopleura dioica, end joining of linear DNA fragments leads to deletions larger than in ascidians and human
This graph shows that in Oikopleura dioica, end joining of linear DNA fragments leads to deletions larger than in ascidians and human cells. The same and almost systematic deviation is observed in the repair of CRISPR induced breaks.
Photo:
Chourrout Group

Deng et al. published  «Prevalence of Mutation-Prone Microhomology-Mediated End Joining in a Chordate Lacking the c-NHEJ DNA Repair Pathway» Current Biology 28(20):3337-3341

A DNA repair pathway shared by virtually all eukaryotes is assumed to be essential. Previous genome study in Oikopleura had suggested an absence of NHEJ, a major Double Strand Break (DSB) repair pathway. This work indeed shows with experiments mimicking or inducing double strand breaks with CRISPR that Oikopleura DSBs are being repaired by a mechanism of end joining that is microhomology dependent and more mutation prone than NHEJ. Furthermore, the study of indel polymorphism tends to support that the mechanism has contributed to high level of genomic divergence. The big enigma is why such a universal DNA repair pathway has been eliminated, for example by negative selection if it had become deleterious in the particular context of tunicate larvaceans.

See how the paper was referred to and analysed by David E.K. Ferrier and Shunsuke Sogabe in their dispatch entitled "Genome Biology: Unconventional DNA Repair in an Extreme Genome" (Current Biology, Volume 28, Issue 20, Pages R1208-R1210)