Co-localization of keratin 6a (K6a) expression with markers of mammary epithelium. Indirect immunofluorescence was performed on mammary gland sections from 6-week FVB mice, containing both terminal end buds (left column) and ducts (right column). K6a staining is shown in green for all sections. Co-localization was performed for smooth muscle α-actin (a,b), K8 (c,d), estrogen receptor α (e,f), and bromodeoxyuridine (h,i), which are all shown in red. Quantification of K6a-positive cells co-expressing estrogen receptor α or bromodeoxyuridine is shown in the bar graphs (g,j). Scale bar, 50 μm.