The transgene consists of a mouse Plp promoter region (exons 1 and 2) and a cre-ESR1 cassette. The human ESR1 sequence is mutated at G400V, M543A, and L540A in the ligand-binding domain to allow activation by 4-hydroxytamoxifen (OHT) and ICI 182,780. 15 kb of mouse Plp promoter sequences drive transgene expression in oligodendrocytes and Schwann cells.