ИСТИНА

Sponges have excellent regenerative abilities, varying from the restoration of lost body fragments to the whole body regeneration. The study of the reparative regeneration showed that in different taxa it is provided by different cellular mechanisms: (1) through accumulation of pluripotent cells and the dedifferentiated cells (blastema), or (2) through remodeling of intact tissue near the wound, based on epithelial morphogenesis. The first type is typical for Demospongiae, and the second for Homoscleromorpha and Calсarea. We have combined morphological, cytological, RNA-seq, whole-mount in situ hybridization and in silico approaches to study mechanisms of morphogenetic events during regeneration in severa sponge species from Homoscleromorpha, Demospongiae, and Calcarea. Epithelial morphogenesis, mainly spreading and fusion of epithelial sheets was found to be the key morphogenetic process during regeneration for Homoscleromorpha and Calcarea, while mesenchymal morphogenesis by mesenchymal-epithelial transformations is the main mechanism during Demospongiae regeneration. Neither cell proliferation nor apoptosis play a significant role in the regeneration in sponges. Cell transdifferentiation plays an important role in the regeneration of all sponges, regardless of their phylogenetic position, its anatomy, or the type of aquiferous system. Using transcriptomics, we found that among the molecules that change their expression both shortly after damage and during pattern recovery, there are a large number of transcription factors and participants in signaling cascades, in particular, the Wnt pathway. Using in situ hybridization, we showed that Wnt and TGF-beta change their expression at different stages of regeneration. This observation confirms that these signaling pathways are involved in the patterning of the sponge body during its recovery after injury. Altogether, we demonstrate that regeneration in sponges involves a variety of processes utilized during regeneration in other animals and points to the particular importance of transdifferentiation in this process. This study was supported by the Fund of President of the Russian Federation grant no. MK-1096-2021-14 and Russian Foundation for Basic Research grant no. 21-54-15006.