Nance-Horan syndrome, characterized by congenital
cataracts, craniofacial, dental abnormalities and mental disturbances, is an X-linked disorder with significant phenotypic heterogeneity. Affected individuals have mutations in the NHS (
Nance-Horan syndrome) gene typically resulting in premature truncation of the
protein. This report underlines the complexity of the regulation of the NHS gene that transcribes several
isoforms. We demonstrate the differential expression of the two NHS
isoforms, NHS-A and NHS-1A, and differences in the subcellular localization of the
proteins encoded by these
isoforms. This may in part explain the pleiotropic features of the syndrome. We show that the endogenous and exogenous NHS-A
isoform localizes to the cell membrane of mammalian cells in a cell-type-dependent manner and that it co-localizes with the tight junction (TJ)
protein ZO-1 in the apical aspect of cell membrane in epithelial cells. We also show that the NHS-1A
isoform is a cytoplasmic
protein. In the developing mammalian lens, we found continuous expression of NHS that became restricted to the lens epithelium in pre- and postnatal lens. Consistent with the in vitro findings, the NHS-A
isoform associates with the apical cell membrane in the lens epithelium. This study suggests that disturbances in intercellular contacts underlie cataractogenesis in the
Nance-Horan syndrome. NHS is the first gene localized at TJs that has been implicated in congenital
cataracts.