With Licence to Mutate
Loss of a DNA repair pathway in Oikopleura
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)