Analysis of mouse side population (SP) cells. Flow cytometric analysis of mouse cells stained with Hoechst 33342: (a) SP in mouse mammary epithelial cells (box), (b) SP in mouse bone marrow cells. X axis, Hoechst red fluorescence intensity (FL5); Y axis, Hoechst blue fluorescence intensity (FL4). (c) RT-PCR analysis of ABC transporter cassette proteins in SP and non-SP cells from mouse mammary epithelial cells. M, molecular weight marker; Brcp1, breast cancer resistance protein; Mrp, multidrug resistance-associated protein. Sizes of bands: Brcp1, 327 bp; Mrp1, 701 bp; Mrp3, 301 bp; Mrp4, 222 bp.