ИСТИНА

Cytoskeletal studies in sponges are fragmentary and focus mainly on the qualitative description of existing filamentary systems. However, in the absence of neurohumoral regulation and, thus, higher levels of cell connectivity, morphogenetic processes (both physiological and upon injury) depend on cytoskeletal rearrangements, its regulation through evolutionary conservative signalling pathways, and intercellular interactions. Research considering these mechanisms provides valuable data in the field of evo-devo. We studied two sponges from phylogenetically distant clades having different ecological niches: filtering calcareous sponge Leucosolenia corallorrhiza and carnivorous demosponge Lycopodina hypogea. Immunocytochemical studies were combined with confocal microscopy to describe cytoskeletal structures (actin filaments, microtubules). Time-lapse imaging, RT-qPCR and WB were used to perform functional inhibitory analysis on two different models: regeneration in calcareous sponge and nutrition cycle in demosponge. Regeneration in Leucosolenia manifests in the formation of regenerative membrane (RM) – three-layered structure sealing the wound. The main mechanism for its formation – cell shape changes and transdifferentiations in two epithelial-like layers: exopinacoderm and choanoderm. The main force that coordinates cells and pulls the membrane towards the wound is a contractile actomyosin cable. Regeneration dynamics can be disrupted with direct inhibition of myosin ATPse activity, as well as inhibition of Rho / ROCK signalling pathway components. Immunocytochemical analysis of Lycopodina tissues demonstrates high contractility. Pharmacological inhibition of actomyosin contractility can significantly alter the dynamics of the nutrition cycle. Cytoskeletal rearrangements and their regulation during various morphogenetic processes characteristic of sponges can complement the data on basal metazoans and clarify the establishment of multicellularity itself.