Fig. 4. An overall model of cellular organization in the oesophageal epithelium. The IBL cells constitute the epithelial stem cell compartment (red). IBL cells proliferate infrequently and asymmetrically. Transit amplifying cells reside in the epibasal layers (gray). PBL cells (green) are intermediate in behavior between IBL and epibasal cells (see text). Differentiated squames are shown in yellow. PBL cells probably migrate off the tips of the oesophageal papillae as suprabasal integrin expression is a consistent finding at this site (Seery and Watt, 2000). This phenomenon is seen in the epidermis when rapidly proliferating cells migrate out of the basal layer (Rikimura et al., 1997). [Figure reprinted from (Seery and Watt, 2000) with permission from Elsevier Science].