COMPARISON OF CELL REPLACEMENT IN BONE-MARROW, TESTIS AND 3 REGIONS OF SURFACE EPITHELIUM

What fraction of the proliferative pool cells in epithelial tissues functions as stem cells is still uncertain. Earlier models, based on little or no good evidence, have assumed that this fraction is close to one. Recently there have been developments suggesting that the fraction of stem cells is low, with considerable cell production being attributable to division in short-lived transit proliferative cells. This brings epithelial tissues into line with haematopoiesis and spermatogenesis. This review considers these newer developments and emphasises the similarities between three epithelial regions (skin, tongue and intestine) and bone marrow and testis. Some of the models currently under discussion relate cell position, division polarity, protection of stem genome and hence carcinogenesis. Some of the implications of these models are discussed. © 1979.