ИСТИНА

Hydrozoan cnidarians at the polyp stage form highly elaborated colonies with a variety of branching patterns that makes them ideal models for studying the mechanisms of body plan diversification. Our study is focused on the molecular mechanisms of colony patterning in the non-model hydrozoan Dynamena pumila. Dynamena colony consists of stolons and monopodialy branching shoots. Both structures grow due to activity of terminally located growth tips: the shoot growth tip and the stolon growth tip. In the course of colony growth, shoot growth tip is repeatedly divided into three parts: two lateral hydrants and the central shoot growth tip primordium. It is well known that the canonical Wnt/β- catenin (cWnt) signaling pathway plays a crucial role in the establishment of the oral-aboral axis in cnidarians. However, a role for cWnt signaling in the spatial patterning of structurally complex hydrozoan colonies is not clear. We provide evidence suggesting that the key components of cWnt pathway (β- catenin, tcf) and the Wnt-responsive gene, Brachyury 2, are involved into specification and patterning of shoot growth tip. Pharmacological experiments indicate that hyper-activation of the cWnt pathway abolishes the formation of shoot growth tips, but not stolon growth tips in a young Dynamena colony. This leads to development of a stolonal colony characteristic for other hydrozoan species. Inhibition of Wnt/β-catenin pathway arrests the formation of shoot growth tips, but restoration of cWnt signaling leads to transdifferentiaton of shoot growth tip primordium into stolon growth tip. Our findings demonstrate that a fine-tuning of the canonical Wnt signaling could be one of the leading factors in the evolution of the spatial organization of hydrozoan colony. This work is funded by Russian Foundation for Basic Research, grant number 17-04-01988 A.