RNA Synthesis and Processing during Cytodifferentiation in Fetal Rat Pancreas

Abstract

In fetal rat pancreas cytodifferentiation occurs between day 14 and day 20 of gestation and is accompanied by an exponential increase in the cellular accumulation of tissue specific proteins and an elaboration of the cellular organelles associated with their synthesis and secretion. Evaluation of RNA synthesis by [3H] uridine incorporation into trichloroacetic acid precipitable material showed that during this period the apparent rate of RNA synthesis increased 7.5 fold from 2 x 10(3) dpm/micrograms DNA/h on day 15 to 1.5 x 10(4) dpm/micrograms DNA/h on day 19; [3H] leucine uptake showed that the rate of protein synthesis increased about the same extent with the major difference being that the maximum rate of protein synthesis occurred on day 19, one day after the maximum rate of RNA synthesis. The soluble pyrimidine nucleotide pools decreased from 122 pmol/micrograms DNA on day 14 to 15 pmol/micrograms DNA on day 16 followed by an increase to 104 pmol/micrograms DNA on day 19; the purine nucleotide pools decreased from 367 pmol/micrograms DNA on day 14 to 286 pmol/micrograms DNA on day 16 and then increased to 635 pmol/micrograms DNA on day 19. These values roughly paralleled the transitions observed in the rates of RNA and protein synthesis. Agarose-acrylamide slab gel electrophoresis showed an increase in RNA synthesis and an increase in ribosomal RNA synthesis and processing with cytodifferentiation.