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Lixing W Reneker, Lanlan Wang, Girish Chandran, Abby Lueckenotte, Rebecca Irlmeier; Conditional Deletion of Apaf-1 Disrupts Mouse Lens and Anterior Segment Development. Invest. Ophthalmol. Vis. Sci. 2016;57(12):No Pagination Specified.
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© ARVO (1962-2015); The Authors (2016-present)
In our previous study on the role of programmed cell death (PCD) in lens and anterior segment development, we used mutant mice that are defective in mitochondrial-mediated apoptosis pathway, including cytochrome c KA knock-in and Apaf-1 knockout mice. We found that activation of this classical apoptosis pathway is required for lens-corneal separation and for normal anterior segment morphogenesis. Furthermore, lenses in Apaf-1-null embryos were significantly smaller than control lenses. Because Apaf-1-null embryos die before embryonic day 17.5 (E17.5), the role of Apaf-1 in lens development has not been delineated. The purpose of this study is to use Apaf-1 conditional deletion mutant to assess its function in lens development.
The ocular surface ectodermal Cre line (LeCre) was used to cross with Apaf-1-flox mice to generate conditional deletion mutant LeCre;Apaf-1flox/flox (referred as Apaf-1-CKO) mice. Developmental defects in mutant eyes and lenses were analyzed by histology and immunohistochemistry.
Apaf-1-CKO mice displayed severe anterior segment defects including persistent lens stalk, absence of anterior chamber, iridocorneal angle and corneal endothelium. The similar defects were seen in the mitochondrial death pathway deficient mutant embryos mentioned in the “Purpose”, suggesting that conditional deletion of Apaf-1 in surface ectodermal cells disrupts PCD that is required for lens-corneal separation. In contrast to the lenses in cytochrome c KA knock-in mutant mice which looked normal, the lenses in Apaf-1-CKO mutant at E13.5 were significantly smaller than the control lenses, the same lens defect was also developed in the Apaf-1-null mutant embryos. In postnatal Apaf-1-CKO lenses, the epithelial layer was thin and attenuated, and fiber cell mass showed degenerative phenotype. Expression of Pax-6 and c-Maf was normal in Apaf-1-CKO lenses at E13.5 but was downregulated in the postnatal mutant lenses. Changes in cell proliferation and differentiation are currently under investigation.
Loss of Apaf-1 results in persistent lens stalk and anterior segment dysgenesis, and severe lens defects in later developmental stage. Our results suggest that Apaf-1 is required not only for activation of PCD during early steps of lens and anterior segment development, but also for normal lens cell proliferation and fiber differentiation at later stage.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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