Sponges (Porifera) represent one of the most ancient metazoan lineages. They possess unique anatomical and tissue structure, making them promising models for evolutionary studies. The high plasticity of sponge tissue and cells provide them with outstanding recovery abilities, ranging from wound healing to re-building of a functional body from dissociated cells.

We have combined several microscopy techniques to elucidate morphogeneses, cellular mechanisms and cell sources during reparative regeneration and cell reaggregation in five species from different clades: Halisarca dujardinii (Demospongiae), Aplysina cavernicola (Demosponigae), Sycon sp. (Calcarea), Leucosolenia variabilis (Calcarea) and Clathrina arnesenae (Calcarea).

The main mechanism of reparative regeneration in studied Demospongiae is cell migrations and epithelio-mesenchymal transformations, involving archaeocytes and choanocytes, which are a cell source for the recovery of lost structures. In contrast, the reparative regeneration in Calcarea occurs due to extensive remodeling of intact tissues near the wound through epithelial morphogeneses, accompanied by cell transdifferentiations.

The cell reaggregation in both Demospongiae and Calcarea involves mass cell dedifferentiation on the early stages of the process. During progressive development of multicellular aggregates, individual cell migrations and transdifferentiations ensure restoration of required cell types and intact anatomical structures. However, epithelial morphogeneses contribute to the development of calcareous sponge aggregates.

Thus, during recovery processes, sponges utilize diverse and complex morphogenetic mechanisms, with a particular importance of cell transdifferentiation. While all sponges demonstrate high recovery abilities, the morphogeneses and cell sources for the recovery of lost structures varies in different clades.
The study was support by RFBR nos.16-04-00084, 16-34-00145, 19-04-00545 and 19-04-00563 and RSF no.17-14-01089.