ИСТИНА

Multicellular animals arose along with complex gene programs controlling tissue integrity. Sponges are an essential group for revealing the stepping stones of metazoan evolution. Here, we present demosponge Halisarca dujardinii as a promising model for exploring conserved mechanisms maintaining tissue homeostasis in Metazoa. Using bulk RNA sequencing and recent genomic data, we described major changes in gene expression during distinct modes of regeneration: reaggregation from single cells and reparative regeneration of body wall. Weighted gene coexpression network analysis (WGCNA) revealed conserved regulatory framework and common set of key transcription factors participating in the restoration of tissue integrity. Tissue damage results in drastic upregulation of genes responsible for cell signalling (e.g., Wnt and Hippo pathways). The upregulation of epithelial-mesenchymal transition (EMT) program and cell dedifferentiation in this sponge is surprisingly associated with the overexpression of epithelial markers. Stem cell maintenance programs also show early response to the tissue disruption, being transcriptionally decoupled with cell cycle machinery: while we observed an increase in the expression of stem cell markers, cell cycle seems to be downregulated during the regeneration. Altogether, current morphological and RNA-seq data render both whole-body and body wall regeneration as reparative processes relying primarily on cell plasticity rather than cell proliferation.