title: A γA-Crystallin Mouse Mutant Secc with Small Eye, Cataract and Closed Eyelid.
abstract: Cataract is the most common cause of visual loss in humans. A spontaneously occurred, autosomal dominant mouse mutant Secc, which displayed combined features of small eye, cataract and closed eyelid was discovered in our laboratory. In this study, we identified the mutation and characterized the cataract phenotype of this novel Secc mutant. The Secc mutant mice have eyelids that remain half-closed throughout their life. The mutant lens has a significant reduction in size and with opaque spots clustered in the centre. Histological analysis showed that in the core region of the mutant lens, the fiber cells were disorganized and clefts and vacuoles were observed. The cataract phenotype was evident from new born stage. We identified the Secc mutation by linkage analysis using whole genome microsatellite markers and SNP markers. The Secc locus was mapped at chromosome 1 flanked by SNPs rs3158129 and rs13475900. Based on the chromosomal position, the candidate cataract locus γ-crystallin gene cluster (Cryg) was investigated by sequencing. A single base deletion (299delG) in exon 3 of Cryga which led to a frame-shift of amino acid sequence from position 91 was identified. As a result of this mutation, the sequences of the 3rd and 4th Greek-key motifs of the γA-crystallin are replaced with an unrelated C-terminal peptide of 75 residues long. Coincidentally, the point mutation generated a HindIII restriction site, allowing the identification of the CrygaSecc mutant allele by RFLP. Western blot analysis of 3-week old lenses showed that the expression of γ-crystallins was reduced in the CrygaSecc mutant. Furthermore, in cell transfection assays using CrygaSecc mutant cDNA expression constructs in 293T, COS-7 and human lens epithelial B3 cell lines, the mutant γA-crystallins were enriched in the insoluble fractions and appeared as insoluble aggregates in the transfected cells. In conclusion, we have demonstrated that the Secc mutation leads to the generation of CrygaSecc proteins with reduced solubility and prone to form aggregates within lens cells. Accumulation of mutant proteins in the lens fibers would lead to cataract formation in the Secc mutant.
authors: School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong SAR, China.
authors: Man Hei
authors: MH
authors: Cheng
authors: School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong SAR, China.
authors: Chung Nga
authors: CN
authors: Tam
authors: Department of Obstetrics and Gynaecology, The Chinese University of Hong Kong, Hong Kong, China.
authors: Kwong Wai
authors: KW
authors: Choy
authors: School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong SAR, China.
authors: Wai Hung
authors: WH
authors: Tsang
authors: School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong SAR, China.
authors: Sze Lan
authors: SL
authors: Tsang
authors: Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong, China.
authors: Chi Pui
authors: CP
authors: Pang
authors: School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong SAR, China.|Centre for Reproduction Development and Growth, Li Ka Shing Faculty of Medicine, Pokfulam, Hong Kong SAR, China.
authors: You Qiang
authors: YQ
authors: Song
authors: School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong SAR, China.|Centre for Reproduction Development and Growth, Li Ka Shing Faculty of Medicine, Pokfulam, Hong Kong SAR, China.
authors: Mai Har
authors: MH
authors: Sham
mesh_terms: D000818:Animals; D019556:COS Cells; D002386:Cataract / Q000235:genetics* / Q000378:metabolism; D002522:Chlorocebus aethiops; D004252:DNA Mutational Analysis; D005124:Eye Abnormalities / Q000235:genetics*; D005141:Eyelid Diseases / Q000235:genetics*; D008040:Genetic Linkage; D060005:Genotyping Techniques; D007908:Lens, Crystalline / Q000378:metabolism / Q000473:pathology; D008810:Mice, Inbred C57BL; D038222:gamma-Crystallins / Q000235:genetics*
chemical_list: D038222:gamma-Crystallins