Evolution_of_programmed_DNA_elimination_in_free_living_Oscheius_nematodes

In most animals, the germline genome is segregated from the soma. In some species the somatic genome differs from the germline through a process of programmed DNA elimination (PDE). We previously identified PDE in the free-living nematode Oscheius tipulae from whole genome sequencing. We have now sequenced the genomes of four additional Oscheius species. All four also undergo PDE, eliminating up to 3.7% of the genome from sub-telomeric and chromosome-internal sites, generating new telomeres to which short arrays of telomeric repeat are added. Each elimination site is characterised by a conserved 21-base motif. Chromosome-internal elimination results in additional chromosomes in somatic cells, and internal sites are associated with chromosomal rearrangements between species. Eliminated DNA is not enriched for repeats, and no genes are consistently removed. These data support a model where PDE is part of germline control of the disposable soma by promotion of senescence through shortened telomeres.