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L. Li, C.-H. Xia, B. Chang, X. Gong; Studies of Genetic Suppressor for Nuclear Cataracts. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5186.
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To identify the genetic modifier(s) of C57BL/6J (B6) strain background that suppresses a nuclear cataract caused by a loss of alpha3 connnexin (Gja3 or Cx46) and to investigate the molecular mechanism for the prevention of nuclear cataract formation.
A genome-wide linkage analysis was performed on alpha3 knockout mice generated from both intercross and backcross between B6 strain background and 129SvJae strain background. Nuclear cataracts of living animals were evaluated by slit lamp examination. The degree of nuclear opacity was quantitatively measured for the light-scattering by a fiber optic spectrometer. Histology, immunostaining and western blotting were used to determine the cellular and biochemical changes associated with variable nuclear cataracts.
The lod scores of genome-wide linkage analysis indicated genetic modifiers located on chromosome 2 (D2Mit148), chromosome 7 (D7Mit230) and chromosome 9 (D9Mit11). G9 alpha3 knockout mice (9th generation backcrossing into 129 strain background) containing a part of chromosome 7 of B6 strain (B6-chr7) displayed intermediate degree of nuclear cataracts. G10 alpha3 knockout mice with two alleles of B6-chr7 (B6-chr7/B6-chr7) developed mild nuclear cataracts similar to mutant mice in the B6 background while G10 alpha3 knockout mice with two alleles of 129-chr7 (129-chr7/129-chr7) had severe nuclear cataracts. Western blotting results showed that the severity of nuclear cataract was associated with the amount of cleaved alphaB- and gamma-crystallins.
A dominant suppressor of nuclear cataracts is located on chromosome 7 of B6 strain background. The severity of nuclear cataracts is correlated to the amount of cleaved forms of crystallin proteins in alpha3 knockout lenses. This genetic suppressor functions at the upstream to probably inhibit the activation of the calpain II protease, which is responsible for the cleavage of alphaB-crystallin. Fine mapping and candidate gene characterization will lead to the identification of this genetic modifier that prevents nuclear cataract formation.
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