ИСТИНА

Cnidaria is a large phylum comprising mostly marine animals with few freshwater species. Recent phylogenies place them as a sister group to the Bilateria. Unlike Bilateria, clade Medusozoa in the phylum Cnidaria has an evolutionary simple body plan with radial symmetry and one main oral-aboral body axis. As an outgroup to the Bilateria cnidarians have a strategic position to serve as powerful models for investigation of body plan evolution and pattern formation. Our work is focused on molecular mechanisms of oral-aboral axis specification during development of a common White Sea colonial hydroid Dynamena pumila (L., 1758). Wnt signalling is required for the specification of oral pole. Wnt3 and Fzd3 are the components of canonical Wnt signalling pathway and markers of oral and aboral poles of cnidarian body, respectively. Using in situ hybridization we have shown that expression of Wnt3 and Fzd3 is became polarized from preplanula stage. Hence, our results revealed that in Dynamena oral-aboral axis is finally established at the late developmental stages. In contrast, in other cnidarian model organisms Wnt signaling components are localized asymmetrically already in the fertilized egg and animal pole of the egg gives rise to the oral structures. Moreover, according to our results gastrulation morphogenetic movements and expression pattern of body axis markers Wnt3 and Fzd3 appear to be uncoupled in Dynamena unlike in other studied cnidarian model organisms. Furthermore, we are going to investigate the expression of Brachyury transcription factors, presumably the target genes of the canonical Wnt signalling pathway. We have already described expression patterns of these genes on gastrula-planula stages. We have shown that Bra1 is a downstream target of the canonical Wnt signalling pathway. This work is supported by RFBR grant № 17-04-01988a