Genome gymnastics: unique modes of DNA evolution and processing in ciliates

Abstract

In some ciliates, the DNA sequences of the germline genomes have been profoundly modified during evolution, providing unprecedented examples of germline DNA malleability. Although the significance of the modifications and malleability is unclear, they may reflect the evolution of mechanisms that facilitate evolution. Because of the modifications, these ciliates must perform remarkable feats of cutting, splicing, rearrangement and elimination of DNA sequences to convert the chromosomal DNA in the germline genome (micronuclear genome) into gene-sized DNA molecules in the somatic genome (macronuclear genome). How these manipulations of DNA are guided and carried out is largely unknown. However, the organization and manipulation of ciliate DNA sequences are new phenomena that expand a general appreciation for the flexibility of DNA in evolution and development.