Variations in cell plasticity and proliferation underlie distinct modes of regeneration along the antero-posterior axis in the annelid Platynereis.

The capacity to regenerate lost tissues varies significantly among animals. Some phyla, such as the annelids, display substantial regenerating abilities, although little is known about the cellular mechanisms underlying the process. To precisely determine the origin, plasticity and fate of the cells participating in blastema formation and posterior end regeneration after amputation in the annelid Platynereis dumerilii, we developed specific tools to track different cell populations. Using these tools, we find that regeneration is partly promoted by a population of proliferative gut cells whose regenerative potential varies as a function of their position along the antero-posterior axis of the worm. Gut progenitors from anterior differentiated tissues are lineage restricted, whereas gut progenitors from the less differentiated and more proliferative posterior tissues are much more plastic. However, they are unable to regenerate the stem cells responsible for the growth of the worms. Those stem cells are of local origin, deriving from the cells present in the segment abutting the amputation plane, as are most of the blastema cells. Our results favour a hybrid and flexible cellular model for posterior regeneration in Platynereis relying on different degrees of cell plasticity.

A genome resource for the marine annelid Platynereis dumerilii.

The marine annelid Platynereis dumerilii is a model organism used in many research areas including evolution and development, neurobiology, ecology and regeneration. Here we present the genomes of P. dumerilii and of the closely related P. massiliensis and P. megalops, to facilitate comparative genomic approaches and help explore Platynereis biology. We used long-read sequencing technology and chromosomal-conformation capture along with extensive transcriptomic resources to obtain and annotate a draft genome assembly of ~1.47 Gbp for P. dumerilii, of which more than half represent repeat elements. We predict around 29,000 protein-coding genes, with relatively large intron sizes, over 38,000 non-coding genes, and 580 miRNA loci. We further explore the high genetic variation (~3% heterozygosity) within the Platynereis species complex. Gene ontology reveals the most variable loci to be associated with pigmentation, development and immunity. The current work sets the stage for further development of Platynereis genomic resources.