DSSS - Programmed-DNA elimination in Mesorhabditis nematodes

In several species across multiple eukaryotic phyla - from single-celled ciliates to vertebrates - the somatic genome is reduced whereas the germline genome is maintained intact. Although Programmed DNA Elimination (PDE) was first described in 1887, neither the mechanisms, function nor evolution of PDE have been elucidated so far in multicellular eukaryotes due to a lack of genetically-tractable species.

We recently discovered, firstly using cytology, massive PDE in Mesorhabditis, a genus of free-living nematodes, which - in contrast to other historically studied eliminating animal species - is genetically tractable. With preliminary bioinformatic analyses, we showed that elimination mainly concerns repeated elements plus a few species-specific protein-coding genes (Rey & al. doi: 10.1016/j.cub.2023.07.058). Using new sequencing methods, notably combining long-read sequencing (PacBio HiFi, Nanopore) and Hi-C, we have improved the assembly and identified a sequence motif at breakpoints. I will present our strategy to identify the PDE effectors in Mesorhabditis. We and others have also extended our discovery of PDE to many other species within the Rhabditidae family. We are now using this unique set of species with or without PDE (notably C. elegans does not eliminate) to explore the evolution of PDE.