Identification of polydisperse RNA in the cytoplasm of neurons isolated from the immature brain cortex.

The cytoplasmic RNA of 10-day-old rats was studied in bulk-isolated, cortical neurons, obtained under conditions which minimize nuclear contamination. Two RNA fractions, one enriched rRNA and the other in "polydisperse" RNA, were obtained by differential extraction with phenol. Gel electrophoresis and pulse labelling with 5-[3H]uridine were used to confirm the delayed appearance of newly synthesized rRNA in the cytoplasm and to demonstrate its stability. "Polydisperse" RNA appeared in the cytoplasm earlier and had a shorter half-life than rRNA. A wide range of molecular weights for this RNA was found with no predominant individual species. A set of cytoplasmic RNA components of molecular size between 28S and 18S was also present probably reflecting the in vivo degradation of rRNA. The significance of the unexpectedly high amounts of neuronal polydisperse RNA is discussed.