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R. De Iongh, S. Cain, G. Martinez, R. Richardson, M. Kokkinos, H. E. Abud, J. Huelsken, T. Noda, M. L. Robinson; Conditional Mutations of ß-Catenin and APC Reveal Roles for Canonical Wnt Signaling in Lens Development. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1120.
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© ARVO (1962-2015); The Authors (2016-present)
Previous studies indicate that the Wnt/ß-catenin signalling pathway is active and functional during murine lens development. To determine the role of this pathway in lens differentiation we conditionally mutated ß-catenin (Catnß) and adenomatous polyposis coli (Apc) genes to respectively inactivate or activate the pathway in different cellular compartments of the lens.
Two Cre mice lines, which express Cre in fibers only (MLR39) or in fibers and epithelium (MLR10), were used to conditionally mutate phloxed Catnß or Apc alleles during lens differentiation from E12.5. Embryonic and postnatal tissues from mutant and wild-type mice were analysed by PCR, BrdU incorporation, histology and immunofluorescence.
Both intercrosses with MLR10 (ßCat10 and Apc10) resulted in microphthalmia due to disruption of the epithelium and abnormal differentiation of fiber cells. However, neither intercross with MLR39 (ßCat39 and Apc39) showed ocular abnormalities, indicating that Catnß and Apc are not required in differentiated fiber cells. In ßCat10 mice, loss of ß-catenin resulted in epithelial cell cycle arrest, with decreased cyclinD1 and c-myc expression, reduced BrdU and phospho-histone-3 (pH3) labeling and premature cell cycle exit as shown by p57Kip2 labeling. However, there was no evidence of apoptosis. In lenses of Apc10 mice, loss of APC resulted in abnormal activation of Wnt signaling, as evidenced by nuclear ß-catenin staining. In these lenses, at E13.5, there was transient, abnormal cell cycle activation in epithelial and fiber cells (BrdU and pH3). By E15.5 most cells had exited the cell cycle (p57Kip2) and were undergoing aberrant differentiation (abnormal ß-crystallin expression), with some characteristics of EMT (α-smooth muscle actin) and widespread apoptosis.
These data indicate that Catnß and Apc, via the Wnt/ß-catenin pathway, play key roles in regulating proliferation and differentiation of epithelial cells and that the pathway is tightly regulated. Neither gene is required in differentiated fiber cells
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