A sequence motif for DNA double-strand break and telomere healing during programmed DNA elimination
Programmed DNA Elimination (PDE) is an exception to the paradigm of genome integrity, removing selected DNA sequences during development. PDE is observed in hundreds of metazoan species from diverse phyla, but its molecular mechanisms and biological significance in most metazoa remain largely unknown. During PDE in the nematode Oscheius tipulae, DNA double-strand breaks (DSBs) are generated at subtelomeric regions, followed by the loss of DNA at chromosome ends and the healing of the DSBs with de novo telomere synthesis. By mutating a 29-bp degenerated palindromic Sequence For Elimination (SFE) motif at the break sites, we determined the sequence requirement for DSB generation and demonstrated that the conserved GGC/GCC sites are used for neotelomere formation. Introducing the SFE to the retained region adjacent to a native SFE induces DNA cleavage, telomere healing, and loss of additional DNA. Moreover, insertion of the SFE in the middle of the sex chromosome splits it into two functional chromosomes, demonstrating that the SFE function is not constrained by its genomic location. Overall, our data show that the SFE motif is both necessary and sufficient for the generation of DSBs and the healing of DSB ends via telomere addition, playing key roles in Oscheius PDE.