A lentiviral transgenic approach was used to generate these mice. The Tyro-WPRE-FUGW lentiviral transgene (LV2177) was designed with a mouse tyrosinase minigene (Tyro) and woodchuck hepatitis virus post-transcriptional regulatory element (WPRE) in the FUGW self-inactivating HIV-based lentiviral vector backbone. The Tyro minigene replaced the ubiquitin-c promoter and EGFP sequences originally found in the FUGW lentiviral vector. The Tyro minigene is composed of the mouse Tyr enhancer region (623 bp), promoter region (657 bp), and 1566 bp cDNA sequence (including the stop codon); all in sense orientation relative to the FUGW backbone. There is no polyA site between the Tyro minigene and WPRE sequence. The WPRE sequence functions to enhance the mRNA transcript stability. In line OVE2265A, the lentivirus integrates into intron 2 [NCBI37/mm9; 3'-63,825,313(+)] in the antisense orientation.