Circular elimination of germline sequences during programmed genome rearrangement in the ciliate Oxytricha

The ciliate Oxytricha trifallax undergoes complex programmed genome rearrangements during post-zygotic development. Extrachromosomal circular DNA is known to play a role in programmed genome rearrangements in other ciliates, but its extent has not been surveyed in Oxytricha, which has the greatest number of DNA elimination and translocation events of well-studied ciliates. The programmed formation of thousands of extrachromosomal circular DNA molecules found in this study makes Oxytricha a model system for nucleic acid topology, while also yielding mechanistic insight into the process of DNA elimination during Oxytricha genome rearrangements.