Poly(A)-containing RNA in neuroblastoma: immature and differentiated cells in culture

We have analysed the poly(A)-containing RNA from neuroblastoma cells at two different developmental states: either as round, immature neuroblasts grown in suspension, or as differentiated cells exhibiting the morphological properties of mature neurons, when attached to a culture dish. Suspension-grown and monolayer cells were pulse-labelled with tritiated uridine. The profile of cytoplasmic poly(A)-containing RNA from suspension cells is highly heterogeneous with peaks ranging from 16-30 S. The profile obtained from differentiated cells appears somewhat distinct from the previous one. This is evidenced by a relative decrease in the 26-S peak and a virtual disappearance of the 16-S component. In order to compare the 'steady-state' patterns of poly(A)-containing RNA in these two developmental stages, polysomal RNA was prepared from unlabelled cells. Following sucrose gradient sedimentation, each fraction was hybridized to [3H]poly(U). Examination of the two RNA hybridization profiles reveals striking similarities suggesting that 'steady-state' messenger populations include, on the average, the same subspecies. The 16-S fraction, which was not observed after the pulse-labelling of the monolayer culture, is detected here by hybridization to [3H]poly(U) when using polysomal poly(A)-containing RNA from monolayer cells as substrate. These results suggest that terminal differentiation of neuroblastoma cells is not accompanied by major alterations of the transcription program and is paralleled by a marked stabilization of the 16-S species.