LoxP sites were introduced 5' of the Mirn17 gene and 3' of the Mir92-1 gene. The floxed region was followed by an Frt-flanked neomycin cassette. The entire cluster, including Mir17, Mir18a, Mir19a, Mir20a, Mir19b-1, and Mir92-1 is flanked by the inserted loxP sites. (J:134861)