Wnt transfer in the intestinal stem cell niche

• Applicant: Dr. Lorenz Mittermeier
• Subject Area: Cell Biology ; Biochemistry
• Term: from 2019 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 436291821

The ongoing regeneration of the intestinal epithelium is critical for human health and a model for understanding the regulation of adult stem cells in their niche. Wnt signaling regulates the proliferation and differentiation of intestinal stem cells (ISCs). Excessive Wnt signaling induces increased stem cell division leading to adenomas and cancer, while the lack of Wnts causes intestinal atrophy. Consequently, Wnt signals are of the utmost importance for the strict regulation of activity and quiescence of ISCs. Recently, several groups independently demonstrated that the Wnts that control the intestinal stem cell niche are made in specialized stromal cells called telocytes. However, despite the importance of Wnts in stem cell regulation, little is known about how these pivotal regulators are delivered from telocytes to the ISCs. It was proposed that long cellular extensions of the telocytes might be essential for Wnt transfer, since they could enable a directed and precise transmission of Wnts to the ISCs. Related structures, called signaling filopodia or cytonemes, are involved in Wnt transport in other tissues. However, the exact mechanisms underlying formation, regulation and movement of telocyte extensions in the intestine are currently unknown. This research project aims to provide deeper insights into the mechanisms involved in the transmission of Wnts from telocytes to ISCs. This work will be performed in the laboratory of Prof. David Virshup at the Duke-NUS Medical School in Singapore, who is an internationally recognized expert in the field of ISC regulation by the Wnt pathway in health and disease. During my two-year postdoctoral fellowship, I will first visualize the Wnt transmitting apparatus of telocytes by high resolution light sheet and electron microscopy enabling 3D reconstruction to gain insight into the nature of the cellular extensions. Second, I will isolate Wnt secreting stromal cells to identify telocyte-enriched genes potentially important for the Wnt secreting apparatus by next generation sequencing. After selection of particular promising screening hits, expression will be validated by in situ hybridization and immunofluorescence microscopy. Finally, I will characterize selected candidate genes in established functional assays measuring transmission of Wnts from telocytes to ISCs. In summary, this project will illuminate the mechanisms by which Wnts are transported from pericryptal, stromal cells to the stem cells in the intestine to regulate proliferation, differentiation and self-renewal. As Wnt signaling is vital in diverse tissues and malfunctions of this system are often accompanied by cancer, this knowledge will have important implications for other organs and might help to develop novel therapeutic approaches to prevent or treat colorectal cancer and other Wnt-addicted diseases in humans.

• DFG Programme: Research Fellowships
• International Connection: Singapore
• Host: Professor Dr. David Virshup, Ph.D.