Wnt Signaling in Development and Regeneration
Gülçin Çakan – Akdoğan, PhD, Specialist
Ansarullah, Postdoctoral Fellow
Aslı Kartal, PhD Student
Yeliz Garanlı, PhD Student
Betül Haykır, MSc Student
İsmail Küçükaylak, MSc Student
Yağmur Azbazdar, MSc Student
Esra Katkat, MSc Student
Wnt/β-catenin signaling, a vital signal transduction cascade known over the last three decades, takes its name from a family of secreted glycoproteins, the Wnt proteins, which act as pathway ligands and from the downstream effector molecule, β-catenin. Owing to its vital roles in the regulation of embryonic development, maintenance of adult tissue homeostasis and regeneration of various animal tissues and organs (see figure); misregulation of the pathway causes various cancers, genetic disorders, and degenerative diseases. A tight regulation that involves a large number of positive and negative modifiers of the pathway is thus necessary to avoid the detrimental outcomes of pathway misregulation. Understanding the molecular mechanisms of this regulation will help to elucidate its association to human diseases and to develop new potential therapeutic targets.
Our research focuses on two main themes: detailed understanding of Wnt/β-catenin signaling via the discovery of new pathway modulators and exploring the role of Wnt/β-catenin signaling in regeneration of the adult central nervous system by using zebrafish as a model.
On one side, our lab is interested in understanding how Wnt/β-catenin signaling pathway activity is fine tuned i.e. regulated by a variety of positive and negative modulators. Here we have two main lines of research. First, we aim at understanding the role of membrane rafts, which are the specialized cell surface nanodomains known to have critical functions in the regulation of various signaling pathways, in Wnt-receptor complex activation. This is an interdisciplinary study that combines molecular and cellular biology techniques with advanced biophysical methods. Disclosure of the functional role of membrane raft nanodomains in Wnt signal transduction in a broader manner will shed light on the drug discovery studies targeting the pathway proteins preferring rafts.
Second, by exploiting the feedback regulation feature of the Wnt/β-catenin pathway, we aim to characterize novel Wnt targets that might act as pathway modifiers. To identify Wnt target genes, we will apply an RNAsequencing based whole transcriptome analysis and analyze genes that are differentially expressed upon pathway manipulation. Characterization of universally regulated Wnt targets might aid in the discovery of novel Wnt pathway modifiers. Drug candidates that will be discovered via screening of small molecules targeting these modifiers will create a perfect option for targeted treatment of cancer and minimize the side effects that might emerge during treatment. Here we may exploit zebrafish embryos to identify small molecules and further validate them in adult fish.
On the other side, we aim to understand the features of Wnt-responsive cells in the highly regenerative zebrafish brain in response to injury. As zebrafish can constitutively produce new neurons throughout their life at numerous zones of stem/progenitor cells all over the brain, it represents the most widespread vertebrate neurogenesis capacity known to date and thus constitutes an ideal platform to study brain regeneration. Here we will utilize an array of molecular and cellular biology techniques including micromanipulation, histological analyses, and imaging. The outcome will help us understand how brain regeneration is controlled at the molecular level and why regeneration is very limited in the mammalian brain. Furthermore, by revealing the relationship of Wnt signaling to brain regeneration, this study will pave the way for improving brain regeneration and new approaches for the treatment of neurodegenerative diseases or brain injury.
Activation of Wnt/β-catenin signaling at the plasma membrane has been shown to occur via phosphorylation of the Wnt co-receptor LRP6 in raft membrane microdomains. However, the functional relevance of this finding for pathway activation and the molecular mechanisms regulating raft-specific activation had remained vague. In our previous work, we identified a new Wnt pathway modulator, Lypd6, as a positive feedback regulator of Wnt/β-catenin signaling and proved that it enhances signaling in zebrafish and Xenopus embryos and in mammalian cells (see figure). Lypd6, a GPI- anchored plasma membrane protein, partitions preferably into the raft membrane domains where it guarantees raft-specific phosphorylation of LRP6, which in turn activates the signaling. Hence, our study reveals that the activation of Wnt pathway components in specific plasma membrane microdomains is a target for cellular modifiers of the pathway. Future studies will not only elucidate the molecular mechanisms underlying such regulation but will also reveal whether these principles could be adopted for therapeutic interventions.
|AWARDS AND RECOGNITION
• Turkish Academy of Science (TÜBA) Young Scientist (GEBİP) Award 2016
• Academy of Science Young Scientist (BAGEP) Award 2016
• L’Oréal & Unesco Turkey National Women in Science Award 2015
• TÜBİTAK and The Marie Curie Action COFUND (FP7) 2015, Scientific Advisor
• EMBO Installation Grant 2014
• Scientific and Technological Research Council of Turkey (TUBITAK) Reintegration Fellowship 2014
Full list and citations: Google Scholar: Gunes Ozhan
• Sezgin E, Azbazdar Y, Ng XW, Teh C, Simons K, Weidinger G, Wohland T, Eggeling C, Ozhan G. Binding of canonical Wnt ligands to their receptor complexes occurs in ordered plasma membrane environments. FEBS J. 2017 Aug; 284(15): 2513-2526.
• Schneider F, Waithe D, Clausen MP, Galiani S, Koller T, Ozhan G, Eggeling C, Sezgin E. Diffusion of lipids and GPI-anchored proteins in actin-free plasma membrane vesicles measured by STED-FCS. Mol Biol Cell. 2017 Jun 1;28(11): 1507-1518.
• Gunes Ozhan and Gilbert Weidinger. Wnt/beta-catenin signaling in heart regeneration. Cell Regen (Lond). 2015 Jul 8;4(1):3.
• Kizil C*, Küchler B*, Yan JJ*, Ozhan G, Moro E, Argenton F, Brand M, Weidinger G and Antos CL. Simplet/Fam53b is required for Wnt signal transduction by regulating β-catenin nuclear localization. Development. 2014 Sep;141(18): 3529-39. *equal contribution.
• Wehner D, Cizelsky W, Vasudevaro MD, Ozhan G, Haase C, Kagermeier-Schenk B, Röder A, Dorsky RI, Moro E, Argenton F, Kühl M, Weidinger G. Wnt/β-Catenin Signaling Defines Organizing Centers that Orchestrate Growth and Differentiation of the Regenerating Zebrafish Caudal Fin. Cell Rep. 2014 Feb 13;6(3):467- 81.
• Luz M, Spannl-Müller S, Ozhan G, Kagermeier-Schenk B, Rhinn M, Weidinger G, Brand M. Dynamic Association with Donor Cell Filopodia and Lipid-Modification Are Essential Features of Wnt8a during Patterning of the Zebrafish Neuroectoderm. PLoS One. 2014 Jan 10;9(1):e84922.
• Özhan G, Sezgin E, Wehner D, Pfister AS, Kühl SJ, Kagermeier- Schenk B, Kühl M, Schwille P, Weidinger G. Lypd6 enhances Wnt/β- catenin signalling by promoting Lrp6 phosphorylation in raft plasma membrane domains. Dev Cell. 2013 Aug 26;26(4):331-45.
• Moro E, Ozhan-Kizil G, Mongera A, Beis D, Wierzbicki C, Young RM, Bournele D, Domenichini A, Valdivia LE, Lum L, Chen C, Amatruda JF, Tiso N, Weidinger G, Argenton F. In vivo Wnt signalling tracing through a transgenic biosensor fish reveals novel activity domains. Dev Biol. 2012 Jun 15;366(2):327-40.
• Kagermeier-Schenk B, Wehner D*, Ozhan-Kizil G*, Yamamoto H, Li J, Kirchner K, Hoffmann C, Stern P, Kikuchi A, Schambony A, Weidinger G. The transmembrane protein Waif1/5T4 inhibits Wnt/β-catenin signalling and activates noncanonical Wnt pathways by modifying LRP6 subcellular localization. Dev Cell. 2011 Dec 13;21(6):1129-43. *equal contribution.
• Ozhan, G and Weidinger, G. Restoring Tissue Homeostasis: Wnt Signaling in Tissue Regeneration After Acute Injury. Wnt signalling in Development and Disease: Molecular Mechanisms and Biological Functions. May 2014, Wiley-Blackwell. Editors: Stefan P. Hoppler and Randall T. Moon. ISBN: 978-1-118-44416-0.