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E. I. Frolova; Expression of Activated ß-catenin Alters the Patterning of the Optic Cup. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5693.
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© ARVO (1962-2015); The Authors (2016-present)
Progress in elucidating Wnt signaling pathways reveals that Wnt proteins are important molecular regulators involved in the control of differentiation of many tissues, as well as in the maintenance of stem cells and tissue-specific progenitors. However, the role of Wnts in eye development has just begun to be unveiled. Previously, we and others have shown that several Wnts, their receptors and modulators are expressed during early eye development. We hypothesize that Wnts might regulate retinal stem cell differentiation and modulate the partitioning of the optic cup into retina, ciliary epithelium, RPE and optic nerve fields.
To analyze the role of canonical Wnt signaling in optic cup differentiation, we expressed a truncated stabilized form of beta-catenin (constitutively active; CA-catenin) in the optic vesicle using a replication-competent RCAS retroviral vector or plasmid containing the same form of CA-catenin under the control of a CMV/chick ß-actin enhancer/promoter. The plasmids were electroporated into the optic vesicle at stage 10 and the embryos were sacrificed 2-7 days after electroporation. The changes in the optic cup development were analyzed using immunofluorescent staining with the antibodies specific to different optic tissues or in situ hybridization with probes against different isoform of collagen IX.
The expression of CA-catenin in the optic cup led to multiple developmental abnormalities. The large portion of the anterior and ventral parts of the optic cup was expressing the collagen IX implicating that they differentiated into ciliary epithelium. The epithelium in the posterior optic cup contained multiple long protrusions into the vitreous cavity; the protrusions were usually comprised of a one-cell layered epithelium. Immunofluorescent staining with anti-Pax2 and Pax6 Abs showed much of the folded epithelium to be Pax2-positive. The choroid fissure did not close in any treated eyes. In eyes with more than two-thirds of the optic epithelium expressing CA-catenin, the optic nerve could not be morphologically identified. The RPE layer contained large, non-pigmented areas, mostly localized to the dorsal part of the eye. These areas were stained either with Pax2 or Pax6 Abs, but not with markers for the differentiated RPE or retinal neurons. We also observed abnormalities in the lens, cornea and periocular tissues, which were probably the result of abnormal optic cup development.
These results imply that canonical Wnt signaling has distinct effects on different retinal progenitors.
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