A cre/ERT2 along with an Frt flanked neomycin selection cassette, replaces Olig3 coding sequence and was fused in frame with the ATG codon of Olig3. Mutant mice were later crossed with Gt(ROSA)26Sortm1(FLP1)Dym mice to excise the neomycin selection cassette. This is a null allele. (J:143526)