Endogenous exons 2-6 and the LTR insertions in intron 6 were deleted, and a construct containing an HA-tag at the N-terminus of the coding sequence and DNA sequence of exon 2 to exon 7 was inserted. This eliminated the expression of a truncated Dicer isoform in mouse oocytes that is dependent on the LTR insertions. (J:285120)