Sites of RNA synthesis and migration in the adrenal cortex cells of the young rat, as shown by radioautography.

Abstract

The sites of RNA synthesis, processing and migration were studied with light and electron microscope radioautography in adrenal zona fasciculata cells of the young rat. Animals were injected iv with [3H]uridine and sacrificed at various time intervals. A marked radioactive peak was found in blood at the 20 min interval, later time intervals being considered as chase periods. Labelling was high over nucleoli of fasciculata cells at 1 h, with the silver grains concentrated over the fibrillar component. Simultaneous though lower peaks occurred over the condensed chromatin and the interchromatin space. Nucleolar and extranucleolar values were decreased at 8 and 24 h, most silver grains overlaying the cytoplasm at this time period. At 8 h, the granular component of the nucleolus was more heavily labelled than the fibrillar component. This sequence of events suggests a relatively slow uptake of the labelled nucleotides and slow formation of pre-rRNA molecules in the fibrillar component of the nucleolus, with the processing into smaller subunits occurring in the granular component during initial chase. Extranucleolar RNAs were synthesized simultaneously but in a smaller rate. Most nucleolar RNA was finally transferred to the cytoplasm. This pattern will serve as a basis for studying the effects of ACTH on the different steps of RNA synthesis and transport in adrenal cortex cells.