Regulation of αA-crystallin via Pax6, c-Maf, CREB and a broad domain of lens-specific chromatin

Pax6 and c-Maf regulate multiple stages of mammalian lens development. Here, we identified novel distal control regions (DCRs) of the αA-crystallin gene, a marker of lens fiber cell differentiation induced by FGF-signaling. DCR1 stimulated reporter gene expression in primary lens explants treated with FGF2 linking FGF-signaling with αA-crystallin synthesis. A DCR1/αA-crystallin promoter (including DCR2) coupled with EGFP virtually recapitulated the expression pattern of αA-crystallin in lens epithelium and fibers. In contrast, the DCR3/αA/EGFP reporter was expressed only in 'late' lens fibers. Chromatin immunoprecipitations showed binding of Pax6 to DCR1 and the αA-crystallin promoter in lens chromatin and demonstrated that high levels of αA-crystallin expression correlate with increased binding of c-Maf and CREB to the promoter and of CREB to DCR3, a broad domain of histone H3K9-hyperacetylation extending from DCR1 to DCR3, and increased abundance of chromatin remodeling enzymes Brg1 and Snf2h at the αA-crystallin locus. Our data demonstrate a novel mechanism of Pax6, c-Maf and CREB function, through regulation of chromatin-remodeling enzymes, and suggest a multistage model for the activation of αA-crystallin during lens differentiation.