ИСТИНА

Detailed description and analysis of embryonic and post-embryonic development is a prerequisite for further work on different aspect of morphogenesis and general developmental problems in new model species. Different hydrozoan species mostly belonging to the athecates are used as a model species for Evo-Devo projects. Recently only Clytia species within thecate hydrozoans can be considered as a model object due to the developed methods of laboratory cultivation and detailed knowledge of embryonic development. Widely distributed thecate Gonothyraea loveni (Allman, 1859) attracts attention of researches for a long time, but until now our knowledge of its embryonic and early postembryonic development remains fragmentary. The aim of the present work was to obtain the complete (integrated) description of embryonic development of this thecate species. Applying light and electron microscopy, immuno-cytochemistry and CLM we analysed development starting from the early cleavage stages, gastrulation, etc., ending with the development of the planula larva competent to the metamorphosis. Special interest focused on the formation of the nervous system during the larva development. Our results proved the great variability of spatial arrangement of blastomeres during early cleavage stages, leading nevertheless to the stable morula stage. Irrespective of observed variations in blastomeres size, gastrulation occurs via morula delamination. First signs of nerve elements were detected at the preplanula stage characterised by the onset of the embryo elongation along main axis. The nervous plexus of the mature planula larva includes longitudinal and transverse bundles arranged not very regularly. We also attempted to start the investigation of the molecular mechanisms regulating embryonic and post-embryonic development in this species. Wnt-pathway is one of the main embryonic pathways regulating cell proliferation, differentiation and determining the main body axis. Wnt3 is the main secreted factor predetermining the oral-aboral axis in cnidarians embryo. For the first time, mRNA sequence of gene homologous to the Wnt3 was isolated from G. loveni and then was cloned and sequenced. Using real-time PCR we studied the temporal dynamics of this gene expression during normal embryonic development. Spatial distribution of Wnt3 transcripts at different stages of G. loveni embryos development was analysed with the help of in situ hybridization.