Spreading of Wnt/beta-Catenin signal by Cdc42-dependent filopodia in the neural plate of zebrafish

• Applicant: Professor Dr. Steffen Scholpp
• Subject Area: Developmental Neurobiology
• Term: from 2013 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 248775546

Communication of cells by paracrine signaling is essential for developmental processes such as anterio-posterior patterning of the neural plate, tissue regeneration and stem cell regulation and is also a major cause of diseases such as cancer when these types of cell-cell communication becomes de-regulated. The Wnt/β-Catenin signaling is arguably one of the most important paracrine signaling pathways and an important regulator of all of the above-mentioned processes (Logan and Nusse, 2004, Angers and Moon, 2009, Clevers and Nusse, 2012). After Wnts have undergone synthesis, post-translational modification and release from secreting cells, they engage with specific cell surface receptors on nearby cells to elicit a cellular response. In the large and rapidly growing field of Wnt signaling research, there is one fundamental question that is currently not well understood.Which transport mechanisms are used to propagate the lipid-modified Wnt molecules through the aequous extracellular matrix and to form a concentration gradient of Wnt in a vertebrate tissue like the neural plate?There is still considerable debate with respect to the cellular mechanisms that control Wnt morphogen distribution. Diffusion, transcytosis or cellular protrusions have been proposed for the passage of Wnt molecules through a tissue (Port and Basler, 2010). The fact that Wnt ligands are lipid-modified and have a strong membrane affinity determines possible spreading mechanisms. Recently, several specific components that are required for Wnt secretion have been identified in Drosophila. However, little is known about the controlled secretion and transport in vertebrates. During the imaging analysis of our cell communication chip (Efremov et al., 2013) we found that cells send out long filopodia, which display an accumulation of Wnt8 proteins at their tip. Indeed, they make contact to neighboring cells with these filopodia and are able to stimulate the formation of so called signalosomes in the neighboring cells, representing the initial step of signal activation. Preliminary data suggest that the formation of these filopodia depends on Cdc42 function. Indeed, blockage of Cdc42 function reduces Wnt/β-Catenin signaling and consistently overexpression of Cdc42 increases Wnt/β-Catenin signaling in the receiving cells. Interestingly, first data indicate that this mechanism is important for patterning of the early neural plate of a zebrafish embryo. Therefore we hypothesis that filopodia based transfer of Wnt proteins is a novel mechanism for paracrine Wnt morphogen distribution in a vertebrate tissue and we will elucidate this mechanism in detail in this project.

• DFG Programme: Research Grants