Rescue of the genetically engineered Cul4b mutant mouse as a potential model for human X-linked mental retardation

Mutation in CUL4B, which encodes a scaffold protein of the E3 ubiquitin ligase complex, has been found inpatients with X-linked mental retardation (XLMR). However, early deletion of Cul4b in mice causes prenatallethality, which has frustrated attempts to characterize the phenotypes in vivo. In this report, we successfullyrescued Cul4b mutant mice by crossing female mice in which exons 4–5 ofCul4b were flanked by loxPsequences with Sox2-Cre male mice. In Cul4b-deficient (Cul4b