Neuronal restrictive silencing element is found in the KCC2 gene: molecular basis for KCC2-specific expression in neurons.

KCC2 is one of four known isoforms of the K-Cl cotransporter with an expression pattern restricted to neurons. It mediates efflux of Cl- across neuronal membranes and plays an important role in GABAergic and glycinergic neurotransmission. To understand the molecular basis for neuronal specificity of KCC2 expression, we isolated and sequenced portions of the KCC2 gene, including some of its 5' flanking (control) region. We found a 21-bp sequence, within intron 1, that shares 80% homology to the consensus site for neuronal-restrictive silencing factor binding. We demonstrated that this specific sequence of the KCC2 gene promotes transcriptional regulation by showing that nuclear proteins isolated from a mouse neural progenitor cell line interact with this 21-bp element and by establishing that this element silences reporter gene expression in nonneuronal cells.