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Lucy J. Dawes, Yuki Sugiyama, Ana S. Tanedo, Frank J. Lovicu, John W. McAvoy; Wnt-Frizzled Signaling Is Part of an FGF-Induced Cascade that Promotes Lens Fiber Differentiation. Invest. Ophthalmol. Vis. Sci. 2013;54(3):1582-1590. doi: 10.1167/iovs.12-11357.
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It is well established that lens fiber differentiation depends on an FGF-initiated growth factor signaling cascade. Given that recent studies indicate Wnt-Frizzled/Planar Cell Polarity (Wnt-Fz/PCP) signaling has a role in coordinating the orientation and alignment of fibers, this study set out to investigate the relationship between this pathway and FGF-induced fiber differentiation.
Rat lens epithelial explants were cultured with FGF-2. Regulators of Wnt-Fz signaling, secreted frizzled-related protein-1 (Sfrp1), and inhibitor of Wnt production-2 (IWP-2) were applied to assess the role of this pathway in FGF-induced fiber differentiation. A TCF/Lef reporter mouse was used to assess canonical Wnt-Fz/β-catenin signaling.
FGF-induced fiber differentiation was accompanied by upregulation of Wnt-Fz signaling components, Fz3, Fz6, Dishevelled-2 (Dvl2), and Dishevelled-3. During differentiation, Fz and the centrosome/primary cilium translocated to the apical tip/leading edge of similarly polarized groups of cells. Addition of Sfrp1 or IWP-2 to FGF-treated explants inhibited cell elongation and reduced expression of fiber-specific markers, filensin and β-crystallin. Expression of Wnt-Fz signaling components was also reduced and a significant reduction in the active form of Dvl2 indicated inhibition of the pathway. Analysis of the TCF/Lef reporter mouse showed no evidence of canonical Wnt-Fz/β-catenin signaling during FGF-induced fiber differentiation.
This study shows that Wnt-Fz signaling is a component of the FGF-initiated cascade that regulates fiber differentiation. The presence of groups of fibers with Fz and centrosome/primary cilium polarized to the leading edge of each cell is consistent with a role for noncanonical Wnt-Fz signaling in coordinating polarized behavior of differentiating fibers.
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