Non-canonical Wnt signalling in craniofacial skeletogenesis : role of wls, gpc4, wnt5b and wnt9a

• Main Author: Ling, Irving Teck-Cheng
• Published: University of Glasgow 2018
• Subjects: R Medicine (General)
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.744098

Craniofacial development requires progressive morphologic change, proliferation, differentiation and organization of chondrocytes preceding osteogenesis. The Wnt signalling pathway has been involved in regulating bone development and maintenance. As they are fated to become bone, chondrocytes require Wnt to polarize and orientate appropriately to initiate the endochondral ossification program. Although the canonical Wnt signalling has been studied in the context of bone development, the effects of non-canonical Wnt signalling in regulating the timing of cartilage maturation and subsequent bone formation in shaping ventral craniofacial structure is not well understood. In this thesis, I examined the role of the non-canonical Wnt signalling pathway (through the study of the role of wls, gpc4, wnt5b and wnt9a) in regulating zebrafish Meckel’s cartilage maturation to the onset of osteogenic differentiation. First, I show that disruption of wls resulted in a significant loss of craniofacial bone, whereas lack of gpc4, wnt5b and wnt9a resulted in severely delayed endochondral ossification. This demonstrates the importance of the non-canonical Wnt pathway in regulating coordinated ventral cartilage morphogenesis by directing chondrocyte polarity. Second, I found distinct cellular requirements within the body and midzone of the mandible. Without non-canonical Wnt signalling, chondrocytes within the midzone appear to remain in their prehypertrophic state and fail to elongate and stack. This may suggest the importance of Wnt signalling in determining jaw length and size. Third, I generated a double transgenic zebrabow line to allow cellular studies on dynamic cell behaviour during development. Finally, to further interrogate the role of Wnt signalling during chondrocyte maturation, I studied the role of intracellular Wnt trafficking. More recently, there has been increasing evidence that Wnt activity is not only regulated in the receiving cells but also on the level of its secretion (Gross and Boutros, 2013). By studying wntless (wls), a multi-transmembrane protein that shuttles Wnts from the Golgi to the plasma membrane, I found that wls trafficking through coat protein vesicles (COP) is key in neural crest specification and differentiation. These works provide important insights into the non-canonical Wnt signalling during endochondral bone formation and craniofacial lower jaw development.