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Triated actinomycin binding to DNA is closely linked to the degree of repression in chromatin. 3H-AM binding to DNA is the most pronounced in nuclei of cells committed into cycle. Inversely, in cells in the last steps of their differentiation or (and) in the resting state (non-dividing cells), 3H-AM binding for DNA is diminished down to a baseline since it is limited by the deoxynucleoproteins. Epithelial cells of stomach mucosa and duodenum demonstrate an increased cell uptake of tritiated actinomycin from the surface to the bottom of the pits. In severe gastritis and in intestinalysed metaplasia this was abolished: with a uniform enhancement of 3H-AM binding. These findings seem to indicate that these cells are derepressed.

The nuclear binding of H3 actinomycin, which is closely linked to the differentiation phenomenon, was studied in human normal gastric mucosa. Actinomycin binding decreases in cells which differentiate and becomes very low in fully differentiated cells. In the gastric pits, there is a decreasing gradient of labelling from the deeper stem cells to the well-differentiated superficial cells. This indicates that migration and renewal of the surface epithelium occurs following a 'pipe-line' system. All the undifferentiated stem cells are labelled. Where the parietal cells are concerned all degrees of labelling are observed at various levels with a decreasing proportion of labelling from the surface to the bottom of the gland. With mucous cells and chief cells in the upper part of the gland a great number of poorly labelled mucous neck cells is observed. In the middle and lower part of the gland there is a new growth of heavily labelled cells. This means that in the normal human stomach chief cells probably do not originate from mucous cells.