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J Zigler, Lijin Dong, Eric Wawrousek, Stacey Hose, Limin Gu, Guo-Tong Xu, Debasish Sinha; Deletion and mutation of βA3/A1-crystallin produce distinct ocular phenotypes. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3685.
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© ARVO (1962-2015); The Authors (2016-present)
To compare the ocular phenotype of the Nuc1 rat, in which βA3/A1-crystallin is mutated, with that of mice in which βA3/A1-crystallin is absent.
Mice with the βA3/A1-crystallin gene floxed were generated by conventional means, and conditional knockout mice were produced using the Cre-LoxP system. Nuc1 is the result of a spontaneous mutation in the βA3/A1-crystallin gene in the Sprague-Dawley rat which has been well described. Eyes from both models were examined structurally by H&E staining of paraffin sections. Lens crystallins were identified by western blotting with specific antibodies and transcripts by PCR analysis.
In a colony of mice (RPE-cKO) in which βA3/A1-crystallin was conditionally knocked out from the retinal pigmented epithelium, a portion of the animals (~20%) was observed to have microphthalmia, with eyes averaging about 50% of normal mass. Lenses from the microphthalmic eyes were generally transparent, but weighed only about 25% as much as did lenses from normal sized RPE-cKO eyes. Using specific antibodies, the lenses from the microphthalmic eyes were found to lack βA3- and βA1-crystallin proteins, while lenses from the normal sized RPE-cKO eyes had levels of these proteins comparable to wild type lenses. Levels of other crystallins in the lenses from microphthalmic eyes appeared to be in the normal range. In contrast to the very small, but transparent lenses in these mice, lenses rupture prior to birth in the Nuc1 rat and microphthalmia is more extreme. Mutant βA3- and βA1-crystallins are present in the Nuc1 lenses.
Some progeny from matings of RPE-cKO mice appear to be global knockouts of βA3/A1-crystallin. The very small lenses present in these mice suggest that βA3/A1-crystallins are necessary for normal lens, and eye, growth. Homozygous mutation of the βA3/A1-crystallin gene, as seen in the Nuc1 rat, causes a more severe lens and eye phenotype. These findings demonstrate that knockout and mutation of a crystallin can produce strikingly different phenotypes.
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