Disease relevance of Gja8

• Targeted null mutations in Gja8 and Gja3 in mice cause cataracts with recessive inheritance [1].
• 1. The macroscopic and single channel gating characteristics of connexin (Cx) 50 gap junction channels between pairs of N2A neuroblastoma cells transfected with mouse Cx50 DNA were investigated using the dual whole-cell voltage clamp technique [2].

High impact information on Gja8

• Gap junction channels formed by alpha3 (Cx46) and alpha8 (Cx50) connexin provide pathways for communication between the fiber cells in the normal transparent lens [3].
• In addition, double heterozygous knockout lenses retained normal growth and clarity, whereas knockover lenses, where native Cx46 was deleted and homozygously knocked into the Cx50 locus, displayed significantly deficient growth but maintained clarity [4].
• By mating knockin and knockout mice, we show that heterozygous replacement of Cx50 with Cx46 rescued growth but produced dominant cataracts that resulted from disruption of lens fiber morphology and crystallin precipitation [4].
• We recently mapped an autosomal semi-dominant cataract [lens opacity 10 (Lop10)] mutation to mouse chromosome 3 and identified a missense mutation (G-->C) in the Gja8 gene, which causes glycine at codon 22 to be replaced with arginine (G22R) [1].
• We also show that expression of Cx50 in paired Xenopus oocytes induces high levels of voltage-dependent conductance [5].

Biological context of Gja8

• A functional impairment of endogenous alpha 3 connexin is therefore partly responsible for cellular phenotypes in the Lop10 mice [1].
• During an ethylnitrosourea mutagenesis screen, Aey5, a new mouse mutation exhibiting an autosomal dominant congenital cataract was isolated [6].
• Filipin cytochemistry provided indirect evidence that Cx46 and Cx50 expressed alone are recruited into different lipid environments [7].
• CONCLUSIONS: These data indicate that the unique functional properties of both Cx43 and Cx50 are not required for prenatal lens development and that connexin diversity is required for regulation of postnatal growth and homeostasis [8].
• PURPOSE: To determine the roles of intercellular communication in embryonic eye growth and development, mice with a targeted deletion of the Cx43 gene were examined, and mice without both Cx43 and Cx50 were generated and analyzed [8].

Anatomical context of Gja8

• The development of the vertebrate lens utilizes a sophisticated cell-cell communication network via gap junction channels, which are made up of at least three connexin isoforms, alpha8 (Cx50), alpha3 (Cx46) and alpha1 (Cx43), and which are encoded by three different genes [9].
• Structural and immunocytochemical alterations in eye lens fiber cells from Cx46 and Cx50 knockout mice [7].
• To better understand the role of Cx50 in the pathogenesis of congenital cataract, the functional consequences of the D47A mutation in the Xenopus oocyte expression system were studied [10].
• The addition of 3T3 resulted in positive staining of Cx43 and K3 but negative staining of Cx50 in the basal epithelium [11].
• Human HeLa cells transfected with mouse connexin Cx30, Cx46 or Cx50 were used to study the electrical properties of gap junction hemichannels [12].

Associations of Gja8 with chemical compounds

• This missense mutation (D47A) resulted in an aspartate-to-alanine substitution at amino acid position 47 in the first extracellular domain of Cx50 [10].
• Mefloquine also blocked channels formed by the lens gap junction protein, Cx50 (IC(50) approximately 1.1 microM) [13].
• Inversion of both gating polarity and CO2 sensitivity of voltage gating with D3N mutation of Cx50 [14].
• The effect of CO(2)-induced acidification on transjunctional voltage (V(j)) gating was studied by dual voltage-clamp in oocytes expressing mouse connexin 50 (Cx50) or a Cx50 mutant (Cx50-D3N), in which the third residue, aspartate (D), was mutated to asparagine (N) [14].
• In excised membrane patches, application of flufenamic acid or octanol to the extracellular surface of Cx50 hemichannels reduced single channel-open probability without altering the single-channel conductance, but application to the cytoplasmic surface had no effect on the channels [15].

Physical interactions of Gja8

• A G22R point mutation in alpha8 connexin (Cx50) has been previously shown to cause a severe cataract by interacting with endogenous wild-type alpha3 connexin (Cx46) in mouse lenses [16].

Other interactions of Gja8

• Sequence analysis revealed no differences in the Gja5 gene, but identified a T-->C mutation at position 191 in the Gja8 gene, which was confirmed by an additional Mva 12691 restriction site in the genomic DNA of homozygous mutants [6].
• Freeze-fracture and fracture labeling revealed that the junctional assembly, packing organization and topographic interactions between connexons and MP26 differed when Cx46 and Cx50 were co-assembled in the wild-type or expressed separately in the two distinct knockout phenotypes [7].
• CONCLUSIONS: The identified early expression of Cx50, MIP, and Lim2 transcripts in mouse embryonic stages suggests that all three proteins play very important, probably quite different, roles in lens fiber cell differentiation [17].
• Levels of phosphorylated ERK1/2 were identical in wild-type and Cx50-deficient lens epithelia [18].
• Chromosomal assignments of mouse genes for connexin 50 and connexin 33 by somatic cell hybridization [19].

Analytical, diagnostic and therapeutic context of Gja8

• Coupled reverse transcriptase-polymerase chain reaction (RT-PCR) was used to determine gene transcript expression of MIP, Cx50, and MP19 during embryonic development [17].
• A monoclonal antibody directed against MP70 and an anti-Cx50 antibody produced against a synthetic peptide identify the same proteins on western blots and produce identical patterns of immunofluorescence on frozen sections of rodent lens [5].
• Immunostaining and Western blot analysis were used to determine protein expression of K3, Cx43, and Cx50 [11].

References