A [gamma]A-Crystallin Mouse Mutant Secc with Small Eye, Cataract and Closed Eyelid

• Published in: PloS one Vol. 11; no. 8; p. e0160691
• Main Authors: Cheng, Man Hei, Tam, Chung Nga, Choy, Kwong Wai, Tsang, Wai Hung, Tsang, Sze Lan, Pang, Chi Pui, Song, You Qiang, Sham, Mai Har
• Format: Journal Article
• Language: English
• Published: Public Library of Science 11.08.2016
• Subjects: Care and treatment; Cataracts; Diagnosis; Eye; Gene mutation; Genetic aspects; Physiological aspects; China
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0160691

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 [gamma]-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 3.sup.rd and 4.sup.th Greek-key motifs of the [gamma]A-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 Cryga.sup.Secc mutant allele by RFLP. Western blot analysis of 3-week old lenses showed that the expression of [gamma]-crystallins was reduced in the Cryga.sup.Secc mutant. Furthermore, in cell transfection assays using Cryga.sup.Secc mutant cDNA expression constructs in 293T, COS-7 and human lens epithelial B3 cell lines, the mutant [gamma]A-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 Cryga.sup.Secc 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.