Summary of two complementary models illustrating Brg1's role during lens fiber cell differentiation. (A) A schematic of the Dnase2b locus including its evolutionarily conserved promoter region (-205 to + 180). Multiple Pax6- and Hsf4-binding sites were identified in the DNase2b promoter and 3'-downstream evolutionary conserved region. Hsf4 and Pax6 recruit (switch/sucrose nonfermentable) (SWI/SNF) complexes as described elsewhere [29, 30]. (B) A schematic of a DNA double-strand break (DSB) accompanied by insertions of H2A histone family, member X (H2AX) histone variant (nucleosomes shown in purple). Both SWI/SNF (including Brg1) and DNA repair (including Nbs1) complexes are then recruited to the chromatin. Both complexes are thought to regulate chromatin structure prior to and during lens fiber cell denucleation. In mouse, Nbs1-deficient lenses show incomplete denucleation of lens fiber cells .