And GSSG (49740, Sigma, St. Louis) were used for standard curve calibration.Lens fibers were subdivided onto cortex and nuclear fraction by a freeze-thawing technique whereby quick freezing at 280uC was followed by thawing at room temperature for 1 min, creating a clear white opacity in nucleus. The cortical and nucleus regions can then be easy separated for GSH and GSSG determination.c-Glutamyl Cysteine Ligase Activity AssayGcl activity in lens extract was measured using monobromobimane derivatization and HPLC analysis with fluorescence detection as previously reported [38].Gracillin site Age-Related 25033180 Nuclear Cataract Animal ModelFigure 4. Slit-lamp image of LEGSKO and age matched wild type mouse lens. (A). Representative images of HOM-LEGSKO mouse lens at 4 and 9 months compared with age 1326631 matched control wild type mouse lens. The same mouse was followed over a period of 9 months and lens images were taken every two months. (B). Slit-lamp images were taken periodically and lens opacity/cataract of any size were recorded for 9 months in homozygous LEGSKO mice vs. age matched wild type mice (n = 30 mice per group). LEGSKO mice developed lens opacities and cataract at much higher rate compared to wild type mice. doi:10.1371/journal.pone.0050832.gAge-Related Nuclear Cataract Animal ModelRNA Extraction and Quantitative mRNA Analysis of Gene ExpressionMinimum Information for Publication of Quantitative RealTime PCR Experiments (MIQE) guidelines [39] was followed for real time PCR analysis. Eyes were removed immediately after sacrifice. Lenses were collected and quickly frozen with liquid nitrogen and stored at 280uC. Total RNA was prepared from single lens using TRIzol reagent (Invitrogen, Grand Island, NY). RNA concentration was measured with a Nanodrop instrument (2000c, Thermal Sci). Only RNA samples with UV 260 nm/280 nm ratio of 1.9?.0 and UV 260 nm/230 nm ratio .1.8 were used for subsequent experiments. For real time PCR, total RNA was deoxyribonuclease-treated (Invitrogen, Grand Island, NY) and transcribed to complementary DNA with oligo(dT) or random hexamer primer (Invitrogen, Grand Island, NY) and Moloney murine leukemia virus reverse transcriptase (New England Biolabs, Ipswich, MA ). Real time PCR was performed with the SYBR Green method and an Applied Biosystems instrument 
(ABI StepOne Plus). Relative expression was calculated using the DDCt method with normalization to constitutive genes as indicated in the figure legends. Specific primer sequences are available on request. All reactions were performed in triplicate. Data analysis was carried out using the cycle threshold values of target gene expression normalized by GAPDH as the internal control.AGEs Determination by LC-MS/MSAmounts of carboxymethyl-lysine (CML) and carboxyethyllysine (CEL), fructose-lysine (FL), methionine sulfoxide (MetSOX), glyoxal immidazolone-1 (G-H1) and methylglyoxal immidazolone1 (MG-H1) in enzymatically digested samples were measured by electronspray positive ionization-mass spectrometric multiple reaction monitoring (ESI+MRM) with a LC-MS/MS system composed of a 2690 Separation module with a Quattro Ultima triple quadropole mass spectrometry detector (Water-Micromass, Manchester, U.K.) following the previously published procedure [40,41]. Analytes 223488-57-1 chemical information released by self-digestion of proteases in assay blanks were subtracted from analytic estimates.Staining of Freshly Isolated Lenses with Hoechst 33342 and Dihydrorhodamine 123 (DHR)Fresh isolated lenses were placed in cham.And GSSG (49740, Sigma, St. Louis) were used for standard curve calibration.Lens fibers were subdivided onto cortex and nuclear fraction by a freeze-thawing technique whereby quick freezing at 280uC was followed by thawing at room temperature for 1 min, creating a clear white opacity in nucleus. The cortical and nucleus regions can then be easy separated for GSH and GSSG determination.c-Glutamyl Cysteine Ligase Activity AssayGcl activity in lens extract was measured using monobromobimane derivatization and HPLC analysis with fluorescence detection as previously reported [38].Age-Related 25033180 Nuclear Cataract Animal ModelFigure 4. Slit-lamp image of LEGSKO and age matched wild type mouse lens. (A). Representative images of HOM-LEGSKO mouse lens at 4 and 9 months compared with age 1326631 matched control wild type mouse lens. The same mouse was followed over a period of 9 months and lens images were taken every two months. (B). Slit-lamp images were taken periodically and lens opacity/cataract of any size were recorded for 9 months in homozygous LEGSKO mice vs. age matched wild type mice (n = 30 mice per group). LEGSKO mice developed lens opacities and cataract at much higher rate compared to wild type mice. doi:10.1371/journal.pone.0050832.gAge-Related Nuclear Cataract Animal ModelRNA Extraction and Quantitative mRNA Analysis of Gene ExpressionMinimum Information for Publication of Quantitative RealTime PCR Experiments (MIQE) guidelines [39] was followed for real time PCR analysis. Eyes were removed immediately after sacrifice. Lenses were collected and quickly frozen with liquid nitrogen and stored at 280uC. Total RNA was prepared from single lens using TRIzol reagent (Invitrogen, Grand Island, NY). RNA concentration was measured with a Nanodrop instrument (2000c, Thermal Sci). Only RNA samples with UV 260 nm/280 nm ratio of 1.9?.0 and UV 260 nm/230 nm ratio .1.8 were used for subsequent experiments. For real time PCR, total RNA was deoxyribonuclease-treated (Invitrogen, Grand Island, NY) and transcribed to complementary DNA with oligo(dT) or random hexamer primer (Invitrogen, Grand Island, NY) and Moloney murine leukemia virus reverse transcriptase (New England Biolabs, Ipswich, MA ). Real time PCR was performed with the SYBR Green method and an Applied Biosystems instrument (ABI StepOne Plus). Relative expression was calculated using the DDCt method with normalization to constitutive genes as indicated in the figure legends. Specific primer sequences are available on request. All reactions were performed in triplicate. Data analysis was carried out using the cycle threshold values of target gene expression normalized by GAPDH as the internal control.AGEs Determination by LC-MS/MSAmounts of carboxymethyl-lysine (CML) and carboxyethyllysine (CEL), fructose-lysine (FL), methionine sulfoxide (MetSOX), glyoxal immidazolone-1 (G-H1) and methylglyoxal immidazolone1 (MG-H1) in enzymatically digested samples were measured by electronspray positive ionization-mass spectrometric multiple reaction monitoring (ESI+MRM) with a LC-MS/MS 
system composed of a 2690 Separation module with a Quattro Ultima triple quadropole mass spectrometry detector (Water-Micromass, Manchester, U.K.) following the previously published procedure [40,41]. Analytes released by self-digestion of proteases in assay blanks were subtracted from analytic estimates.Staining of Freshly Isolated Lenses with Hoechst 33342 and Dihydrorhodamine 123 (DHR)Fresh isolated lenses were placed in cham.