Fig. 2. Propidium iodide staining demonstrates a mitotic cell (BC) in the oesophageal interpapillary basal layer (IBL). Cellular division in the IBL is rare and, as illustrated here, generally occurs at right angles to the underlying basement membrane. This yields one daughter cell that remains in the IBL and one that enters a zone of high proliferative activity (the epibasal layers). Mitoses in the papillary basal layer (not shown) are symmetrical, yielding two daughter cells that remain in contact with the basement membrane.