Figure 3: Luminal cells mainly exhibit symmetrically horizontal divisions.

(a) Immunodetection of dividing luminal cells by staining for CK5 and phosphorylated histone H3 (P-H3, a marker to show the mitotic cell), P63 and laminin, CK8 and P-H3 and AR and P-H3. (b) Defining the spindle orientation of luminal cells by AR and γ-tubulin staining to indicate mitotic spindle orientations of luminal cells, which are either horizontal or vertical to the basement membrane. Yellow arrowheads point to the positions of centrosomes indicated by γ-tubulin staining. (c) Quantification of spindle orientation of luminal cells at different developmental stages of AP prostate lobes (P10, P15 and P20) shows that the spindle orientation of luminal cells is mainly horizontal to the basement membrane. See also Supplementary Table S3 for further data. (d) Analysis of distribution of polarity proteins in dividing luminal cells by staining for ZO-1 and Survivin, Par3 and P-H3, Par3 and Epcam or aPKC and Epcam. Yellow arrowheads indicate the positions of polarity proteins in dividing luminal cells. (e) Confocal analysis of dividing luminal cells by triple staining for Survivin, p63 and CK8 respectively, indicates that the two daughter cells of horizontal divisions of luminal cells are non-basal, luminal cells. Dashed lines in a, b, d, e denote the positions of the basement membrane (bold) and the boundary of dividing luminal cells (light). All sections are counterstained by 4',6-diamidino-2-phenylindole (DAPI) (blue). Scale bars, 10 μm.