Gap junctions containing alpha 8-connexin (MP70) in the adult mammalian lens epithelium suggests a re-evaluation of its role in the lens

A missense mutation in one of the three lens connexins, alpha 8-connexin, h as been recently shown to be the genetic basis of the zonular pulverant len s cataract. This connexin had been considered to be expressed only in lens fibre cells. The present studies show that alpha 8-connexin is also express ed in the lens epithelial cell layer. For this study, the distribution of gap junctions in the adult bovine lens has been investigated by confocal immunofluorescence microscopy using antib odies against alpha 8-connexin (MP70) and alpha 1-connexin (Cx43). In addit ion to the anticipated localisation of a8-connexin to the broad faces of le ns fibre cells as reported in other species, a8-connexin was also found col ocalized with alpha 1-connexin at plaques in the lateral epithelial-epithel ial plasma membranes of the bovine lens. These data suggest that mixed alph a 8-connexin/alpha 1-connexin plaques are between epithelial cells at their apico-lateral plasma membranes, rather than between epithelial and fibre c ells. Indeed, freeze fracture analyses of the epithelial-fibre cell interfa ce failed to reveal gap junctions connecting the epithelium and the underly ing fibre cells. Importantly, microdissection and subsequent immunoblotting of lens epithelium samples confirmed the immunolocalisation results. The d ata suggest mature mammalian lens epithelial cells could form either hetero meric, heterotypic and/or mixed homomeric-homotypic gap junctional complexe s with unique physiological properties, an important point when considering the role of epithelial cell connexins in cataractogenesis. (C) 1999 Academ ic Press.