Pancreas acinar cell differentiation. VII. Autoradiographic demonstration of intracellular radioactivity with with S-adenosyl-L-(C 3 H 3 ) methionine.

After rat pancreas anlagen were grown in an organ culture medium for 9 days and further incubated for 15, 30 or 60 minutes in media to which C(3)H(3)-Sadenosyl-L-methionine (C(3)H(3)-SAM) was added, autoradiography demonstrated radioactivity in the nucleolus, nucleus and cytoplasm of the acinar cell. Under similar circumstances, except that the anlagen were grown in a methionine-deficient (CD-MD) medium prior to incubation with C(3)H(3)-SAM, much greater concentrations of radioactivity were present in the nucleolus, nucleus and cytoplasm of the acinar cell than in the respective compartments of anlagen grown in control medium. The nucleolus showed the highest concentration of radioactivity in anlagen grown in either control or methionine-deficient medium. The nucleolus of the acinar cell of anlagen grown in CD-MD medium appeared to be the most undermethylated cellular compartment and was larger than the nucleolus of the acinar cell grown in the control CD medium, so it is possible that a deficient methylation of ribosomal RNA precursors led to a piling up of RNA in the nucleolus and a decrease in the flow of ribosomal precursors to the cytoplasm. Other substance might have been undermethylated and thereby have inhibited differentiation.