This point mutation occurred in a conserved residue of the extracellular loop 2 motif, which is important in docking selectivity for interactions with other connexins and thereby important in gap junction formation. This mutation is semidominant, causing dense nuclear cataracts evident by 3 weeks of age in both heterozygotes and homozygotes, and microphthalmia only in homozygotes. Lens epithelial cells do not display the typical mosaic pattern, and suture formation of the lens is aberrant in homozygotes. Dampened trans-junctional conductance in paired oocyte expression of this mutant connexin, co-expressed with wild-type GJA8 or GJA3, supports the hypothesis that this mutation functions as a dominant negative. When this mutation is backcrossed onto the C57BL/6J background congenic heterozygotes have normal sized eyeballs, slightly smaller than normal lenses, and very mild nuclear cataracts while homozygotes have microphthalmia with lenses much smaller than normal, dense nuclear cataracts and vacuole-like structures in the lens periphery. This is a more severe phenotype than that of Gja8tm1Scr homozygotes. The disruption of peripheral lens fiber cells to form the vacuole-like structures was found to require Gja3, but the microphthalmia and cataract phenotypes do not.
The Gja8R205G mutation arose spontaneously in the CWXS/Agl recombinant inbred line in the laboratory of Dr. Joe Angel at The University of Texas and was sent to Dr. Bo Chang at The Jackson Laboratory for characterization in 1995. It was maintained on this recombinant inbred background by sibling breeding and sperm was cryopreserved from homozygous males in 2012. This bankstock will be cryo-recovered using C57BL/6J oocytes so the genetic background will be a mixture of CWD/LeAgl, SJL/J, and C57BL/6J. Pups generated by cryorecovery using C57BL/6J oocytes have been proven to display the expected cataract phenotype.
|Gene Symbol and Name||Gja8, gap junction protein, alpha 8|
|Strain of Origin||CWXS/Agl|
|Molecular Note||A spontaneous C-to-G point mutation results in the amino acid substitution of arginine with glycine at position 205 (p.R205G).|