Keratin 6ab (K6ab)-null mammary gland whole-mount analysis. Mammary glands were isolated from intact wild-type (WT) or K6ab-null animals at 6 weeks (a–d) or transplanted WT or K6ab-null tissues were harvested after either 4 weeks of outgrowth (e–h) or 10 weeks of outgrowth after 2 days of treatment with estrogen and progesterone (i–l). Whole-mount staining of the glands to reveal ductal structures is shown at two magnifications. Scale bar, 1 mm. LN, lymph node.