Functional analysis of novel molecular components in head organiser establishment and maintenance in the lower metazoan Hydra

• Applicant: Professor Dr. Suat Özbek
• Subject Area: Developmental Biology ; Biochemistry ; Evolutionary Cell and Developmental Biology (Zoology)
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 278882202

The organizer has a crucial role in setting up the body axes of the developing vertebrate embryo. Diverse morphogens produced and secreted from the Spemann-Mangold organizer tissue orchestrate this process by forming discrete gradients of activatory or repressive factors. In Hydra, the hypostomal head organizer acts as a signalling center that maintains and initiates the primary body axis in steady state polyps and during budding or regeneration. Secreted factors of the Wnt protein family act as primary signalling cues controlling this process. A commonly accepted hypothesis states that a gradient of beta-Catenin activity emanating from Hydras head organizer is responsible for pattern formation by providing positional information to the epithelial cells of the body column. According to the Gierer-Meinhardt theory of de novo pattern formation a diffusible long-range inhibitor is crucial in maintaining this gradient by interacting with the autocatalytic activation center. An autocatalytic feedback-loop based on TCF binding sites in its promotor region has been clearly demonstrated for Hydra Wnt3 that acts as the earliest Wnt ligand in a cascade of Wnt signalling activity during organizer formation. Although several candidates like Hydra Dkk1/2/4 are discussed as possible antagonists, there is no complete picture of the molecular players involved in the proposed activator-inhibitor system in Hydra. In the present application a novel factor is presented that could play a crucial role in this process. A metalloproteinase of the astacin family, designated as Hydra NAS-15-like, has been identified in a screen for Hydra Wnt3 processing factors. NAS-15-like expression is shown to be beta-Catenin-dependent and, in steady-state polyps, to form a gradient reflecting the proposed gradient of beta-Catenin activity in Hydras body. We hypothesize that Hydra NAS-15-like acts downstream of beta-catenin as a negative feedback regulator of Wnt activity on the protein level providing a limitation of high canonical Wnt activity to the hypostomal organiser. Major aims of the application include the elucidation of the substrate specificity of NAS-15-like and its influence on Wnt activity and patterning. In addition, by using a cDNA screen, we want to identify factors that increase Wnt stability in the body column of Hydra and thus facilitate long-range signalling.

• DFG Programme: Research Grants