Programmed genome
rearrangements

We study programmed genome rearrangements in a model species: Paramecium tetraurelia, which carries a ~100 Mb germline genome. During MAC development, the genome undergoes multiple rounds of endoreplication. Concomitantly, massive programmed genome rearrangements eliminate at least 25 to 30% of germline DNA. These rearrangements include (i) removal of repeated sequences (transposons, minisatellites), leading to chromosome fragmentation or heterogeneous internal deletions and (ii) excision of ~ 45,000 short, single copy and noncoding sequences scattered throughout the genome (IES, or internal eliminated sequences).  Precise IES excision is necessary to reconstitute functional open reading frames. At least a fraction of Paramecium IESs are the degenerate remnants of transposons related to the Tc/mariner family.