The targeting vector was designed with (from 5' to 3') an inward-facing lox2272:loxP site, an inverted Shank3 PDZ domain (exons 13-16), another inward-facing lox2272:loxP site and an FRT-flanked neomycin resistance cassette all replacing the corresponding endogenous Shank3 sequences. Flp-mediated recombination removed the FRT-flanked neo cassette.