Germline mutations of the breast tumor suppressor geneBRCA1predispose women to breast and ovarian cancers. However, loss-of-function mutations of mouseBrca1results in recessive embryonic lethality, which obscures the functions ofBRCA1in breast cancer formation. Cre-loxP-mediated tissue-specific knockout was employed to overcome this obstacle. We found that the presence of a ploxP-neo-loxP cassette in intron 10 ofBrca1resulted in severe interference with gene expression. Theneocassette was deleted in either embryonic stem cells or mice to generate theneo-less conditional knockout allele. Finally, we performed functional analysis of mammary tumorigenesis inBrca1conditional knockout mice. The methods to generate and analyze theseBrca1conditional knockout mice are described in this chapter.
