A role for canonical WNT signaling in lens development

Purpose To investigate Wnt signalling in lens development we conditionally deleted β‐catenin (CatnβEx3‐6) or mutated exon3 of β‐catenin (CatnβEx3) or truncated adenomatous polyposis coli (Apc580S) to inactivate or activate the pathway in different cellular compartments of the murine lens. Methods Cre deletor lines that express Cre in fibers only (MLR39) or in fibers and epithelium (MLR10), were used to conditionally mutate floxed CatnβEx3‐6, CatnβEx3 and Apc580S alleles in developing mouse lens from E13. Lenses from mutant and wild‐type mice were analyzed by histology, immunofluorescence and PCR arrays. Results MLR10 intercrosses result in microphthalmia; MLR39 intercrosses show no ocular abnormalities at weaning. Mice with loss of β‐catenin in fibres (MLR39Cre/CatnβEx3‐6) develop cataract in later life. Analyses of MLR10‐derived mutant mice at E13.5 show that loss of β‐catenin inactivates Wnt signals and results in loss of lens cell progenitors, with decreased E‐cadherin, cyclinD1 and cMyc expression, reduced BrdU and phosphohistone3 (pH3) labeling and premature cell cycle exit (p57Kip2). As well as Wnt signal effects, loss of β‐catenin deregulates adherens junctions resulting in loss of hexagonal fibre structure. By contrast, activating mutations of Wnt pathway (CatnβEx3, Apc580S) result in increased epithelial proliferation (BrdU, cyclinD1, PH3), apoptosis (TUNEL) and inhibition of fibre differentiation (β‐crystallin, p57Kip2). Pathway specific PCR arrays confirmed modulation of Wnt signaling in each lens mutant and show altered expression of Notch pathway, indicating these pathways operate as part of a network. Conclusion These data show Wnt signals play key roles in regulating proliferation and differentiation of lens epithelial cells and that the pathway is tightly regulated.