The lens opacity 10 mutation in Gja8 is semidominant. Homozygotes are microphthalmic with foamy cataract of the entire lens apparent when the eyes open at 12 days of age and increasing in opaqueness with age. Bladder cells are found adjacent to the anterior and posterior subcapsular regions of the lens before birth, the lens nucleus begins to liquefy by 4 days of age and ruptures posteriorly, then the lens capsule thickens. Gja8Lop10 Heterozygotes are not microphthalmic and the phenotype associated with the mutation varies according to the genetic background. A nuclear haze or snowflake nuclear opacity is found in F1 heterozygotes of some backgrounds while a more severe dense nuclear opacity is evident by 4 weeks of age in F1 heterozygotes of other backgrounds including AKR/J and BALB/cJ. The F1 heterozygote from C57BL/6J has a more mild phenotype with clear lenses at 4 weeks of age and snowflake nuclear opacity developing later. Mice homozygous for the Gja8tm1Paul targeted mutation, a recessive mutation in which the entire coding region is removed, do not display posterior lens rupture. Additionally, there is a decrease in phosphorylated Gja3 in lens extracts from Gja8Lop10 homozygotes and mice doubly homozygous for Gja8Lop10 and a targeted mutation disrupting Gja3 have a less severe phenotype than that of Gja8Lop10 homozygotes. (Runge et al., 1992; Chang et al., 2002.)
The Lop10 mutation arose spontaneously in the offspring of a BALB/cJ x AKR/J cross at The Jackson Laboratory. It was backcrossed three times to BALB/cJ then maintained by sibling mating. This mutation was later backcrossed onto the C57BL/6J background. At N3 it was made homozygous and after several generations of sibling breeding was subsequently backcrossed 3 more generations to N6 before again being made homozygous.
|Allele Name||lens opacity 10|
|Allele Synonym(s)||G22R; Lop10|
|Gene Symbol and Name||Gja8, gap junction protein, alpha 8|
|Strain of Origin||BALB/cJ x AKR/J|
|General Note||In homozygous mutant mice, eyes are microphthalmic, with a dense white cataract present when eyelids opened at the age of 12 days. Histologic changes could be traced back to the 18th day of gestation. Liquefaction of lens contents had begun by 4 days of age, with posterior herniation by 11 days old. Expression in heterozygotes varied with age and with strain of origin (J:4160).|
|Molecular Note||The mutation in the lens opacity 10 mouse was identifed as a G-to-C missense mutation (C-to-G on forward strand) in the gene, which causes a glycine to arginine substitution at codon 22 of the encoded protein (p.G22R).|