A cassette containing a CMV/beta-actin promoter/enhancer, a loxP-Neo-3xpA-loxP stop signal, A-CREB, an IRES and a nuclear localized EGFP was inserted into the locus via homologous recombination. Acidic CREB (A-CREB) acts as a highly selective pan-dominant-negative reagent to the CREB gene family and consists of an acidic amphipathic extension fused to the N terminus of the CREB leucine zipper domain.