The non-canonical Wnt receptor Ror2 is required for cartilage cell polarity and morphogenesis of the craniofacial skeleton in zebrafish

Abstract

Non-canonical / β-catenin-independent Wnt signaling plays critical roles in tissue / cell polarity in epithelia, but its functions have been less well studied in mesenchymal tissues, such as the skeleton. Mutations in non-canonical Wnt signaling pathway genes cause human skeletal diseases such as Robinow syndrome and Brachydactyly Type B1, which disrupt bone growth throughout the endochondral skeleton. Ror2 is one of several non-canonical Wnt receptor/co-receptors. Here we show that ror2−/- mutant zebrafish have craniofacial skeletal defects, including disruptions of chondrocyte polarity. ror1−/- mutants appear phenotypically wild type, but loss of both ror1 and ror2 leads to more severe cartilage defects, indicating partial redundancy. Skeletal defects in ror1/2 double mutants resemble those of wnt5b−/- mutants, suggesting that Wnt5b is the primary Ror ligand in zebrafish. Surprisingly, the proline-rich domain of Ror2, but not its kinase domain, is required to rescue its function in mosaic transgenic experiments in ror2−/- mutants. These results suggest that endochondral bone defects in ROR-related human syndromes reflect defects in cartilage polarity and morphogenesis.

Loss of dlx5a/dlx6a Locus Alters Non-Canonical Wnt Signaling and Meckel’s Cartilage Morphology

“…Ror2 can interact with Wnt5b during gastrulation in zebrafish and a ror2 null mutant was recently reported to produce craniofacial abnormalities including altered chondrocyte polarity [15,34,43]. Interestingly, the expression of ror2 showed a trend towards more expression at both time points in mutants (Figure 6K).…”

“…The expression of frzd7a show a trend towards higher expression in mutants at 2 dpf followed by lower expression at 3 dpf, potentially to compensate for different amounts of Wnt5b ( Figure 6 J). The tyrosine kinase receptor Ror2 can interact with Wnt5b during gastrulation in zebrafish and a ror2 null mutant was recently reported to produce craniofacial abnormalities including altered chondrocyte polarity [ 15 , 34 , 43 ]. Interestingly, the expression of ror2 showed a trend towards more expression at both time points in mutants ( Figure 6 K).…”

“…This morphogenic movement is governed by the activity of non-canonical Wnts that can alter, among other processes, oriented cell division and cellular morphology [ 12 ]. Indeed, knock-down or knock-out of members of the non-canonical wnt pathways, such as wnt5b , wnt9a , frzd7a , ror2 and wls , resulted in reduced size of PA1 and PA2 structures and changes to chondrocyte cell morphology in zebrafish [ 11 , 13 , 14 , 15 , 16 , 17 ]. Futhermore, loss of wnt5b , wnt9a and ror2 in zebrafish lead to loss in cell polarity in craniofacial structures [ 11 , 15 ].…”

“…Indeed, knock-down or knock-out of members of the non-canonical wnt pathways, such as wnt5b , wnt9a , frzd7a , ror2 and wls , resulted in reduced size of PA1 and PA2 structures and changes to chondrocyte cell morphology in zebrafish [ 11 , 13 , 14 , 15 , 16 , 17 ]. Futhermore, loss of wnt5b , wnt9a and ror2 in zebrafish lead to loss in cell polarity in craniofacial structures [ 11 , 15 ]. However, the upstream signals or genes that regulate the non-canonical Wnt pathway during morphogenesis of jaw structures are still poorly understood.…”

Transforming growth factor beta signaling and craniofacial development: modeling human diseases in zebrafish

“…The first is the acquisition of planar polarity, which mediates convergence-extension movements in the zebrafish craniofacial elements, allowing them to acquire their proper shapes. This is mediated by both Fat/Dchs signaling and noncanonical Wnt signaling, which are critical for the acquisition of chondrocyte polarity during morphogenesis of craniofacial cartilage ( Kamel et al, 2013 ; Le Pabic et al, 2014 ; Sisson et al, 2015 ; Rochard et al, 2016 ; Ling et al, 2017 ; Dranow et al, 2023 ). The second is proper production and secretion of extracellular matrix proteins, which is intimately tied to chondrocyte identity.…”