Related to Fig. 5 . The epidermal BM deforms around dividing basal progenitor cells. (A) Additional example of snapshots taken from time-lapse live imaging movie of basal cell division in E15.5 mTurq2-Col4a1/+;mTmG/mTmG backskin. Interphase, metaphase, and post-cytokinesis stages are shown (left to right). Bottom panel shows same images with membrane curvature measurements shown. Scale bar, 10 µm. (B) Additional example as A. (C) Quantification of the average angle of BM deformation as shown in Fig. 5 F. Data is normalized to the interphase angle for each individual dividing cell. Each line represents one dividing cell. Dark blue line represents the average of all dividing cell lines. n = 23 dividing cells. Error bars = mean + SD. (D) Average intensity projection of backskin from mTmG/mTmG E16.5 embryo labeled with Hoechst (merge, D’) and anti-β4 integrin antibody (merge, D”). (E–E”) Average intensity projection (XZ optical reconstruction) of the image shown in D. (F and G) As D and E, except showing an image taken at 4× zoom. Scale bars, 10 µm. (H–J) Representative TEM images from E18.5 mTurq2-Col4a1/+ embryonic skin showing a dividing basal progenitor cell maintaining hemidesmosome adhesions with the BM during mitotic rounding. BL = basal layer, DEJ = dermal-epidermal junction, HD = hemidesmosome, PM = plasma membrane. Dotted boxes (‘) and (“) in H denote regions magnified in I and J, respectively. Scale bars, 2 µm (H), 100 nm (I), 50 nm (J).