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E. C. Beyer, J. Rodriguez, P. J. Minogue, J. Pal, V. M. Berthoud, L. Ebihara; Molecular Mechanism Underlying a Congenital "Zonular Nuclear" Pulverulent Cataract Associated With a Connexin50 Mutation. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3635.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the cellular and functional consequences of a CX50 (GJA8) mutation, CX50E48K, described in a family with autosomal dominant cataract of the "zonular nuclear" pulverulent type.
Wild type CX50 and CX50E48K were expressed in Xenopus oocytes, and gap junction currents were recorded using the double whole-cell voltage-clamp technique. HeLa cells were transiently transfected with wild type CX50 or CX50E48K subcloned into pcDNA3.1/Hygro(+). The cellular distributions of wild type CX50 and CX50E48K were determined by immunofluorescence microscopy.
Wild type CX50 formed functional channels between Xenopus oocytes with a gap junctional conductance of 5.31 ± 0.44 µS. In contrast, pairs of oocytes injected with the mutant CX50E48K showed no detectable gap junction conductance above control pairs (0.30 ± 0.20 µS). When co-expressed with wild type CX50, CX50E48K did not inhibit gap junctional activity of wild type CX50. Using anti-CX50 antibodies, HeLa cells transfected with wild type CX50 showed immunopositive staining at appositional membranes and in the perinuclear region as expected. In contrast, cells transfected with CX50E48K showed no anti-CX50 immunostaining at appositional membranes, but showed substantial intracellular immunoreactivity. Its distribution overlapped with markers for the ER, ERGIC and Golgi compartments.
These results demonstrate that CX50E48K is impaired in its ability to form gap junctional plaques and acts as a loss of function mutation. The decrease in intercellular communication caused by expression of the mutant connexin may contribute to cataract formation.
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