Volume 83, number 1 FEBS LETTERS November 1977 CHANGES IN THE PATTERN OF POLY(A)-CONTAINING RNA DURING TERMINAL DIFFERENTIATION IN NEUROBLASTOMA CELLS Bernard CROIZAT, Francis BERTHELOT, Armando FELSANI and Franqois GROS Laboratoire de Biochimie Cellulaire, Colldge de France, 11, Place Marcelin Berthelot, 7505 Paris, France Received 4 August 1977 1. Introduction One of the difficulties in analysing the control of genetic expression during the terminal differentiation of somatic cell systems is to decide whether the parameter under study relates to the acquisition of a new phenotype or to more general preparative events, such as the entrance into the post-mitotic stage. In the case of a neuronal system, such as mouse neuroblastoma cells, this situation is complicated by the fact that the developmental stages under comparison often refer to cell populations cultivated in different nutritional or physical conditions. Two stages are often analysed: round immature neuroblasts grown in suspension in the presence of serum or cells exhibiting the properties of mature neurones after being attached to culture dish in the absence of serum. This remark particularly applies to previous obser- vations from the literature in which the synthesis of various enzymes, or of tubulin, have been compared in the course of neuroblastoma differentiation [ 1-4]. It also refers to our previous work on the transcrip- tional activities of immature and differentiated neuroblastoma [5]. Analysis of the hydrodynamic distribution of cytoplasmic poly(A)-containing RNA species from suspension or monolayer grown cells has revealed interesting differences with the virtual disappearance in the latter kind of cells of the 16 S pulse-labelled fraction and a relative variation in the amplitudes of some other fractions. Interestingly the 15 S fraction, observable after pulse-labelling of the suspension grown cells but not after labelling of the monolayer culture, could however be detected in this latter case by hybridization to [3H]poly(U) when using polysomal poly(A)-containing RNA. This was taken as evidence that morphological differentiation does not involve major alteration of the transcription program, but variations at the level of the relative stability of some cytoplasmic messengers. A question that remained unanswered however was whether change~ observed in the pattern of pulse- labelled species did in fact correspond to the morpho- logical events accompanying terminal differentiation or to the modifications in the culture conditions which were experimentally introduced to trigger the develop- mental program. In particular, the relevance of the transition between the logarithmic growth of suspension cells and the postmitotic stationary phase of mono- layer cultures had to be explored. The present study attempts to answer the question. Cytoplasmic poly(A ÷) RNA distribution has been reinvestigated in populations of neuroblastoma attached to culture dish, in a stationary phase, under conditions where no neurite extension occurs. This was achieved by changing the culture conditions in the case of the NIE 115 clone or by using a special neuroblastoma variant, clone NIA 103, which does not undergo morphological differentiation after induc- tion by serum withdrawal [6]. Our results are consis- tent with the conclusion that there is a causality relationship between the changes in the distribution of poly(A)-containing RNAs previously described [5] and the formation of neurites. 2. Materials and methods 2.1. Suspension cultures NIE 115, a clone which has the capacity to mor- phologically differentiate when placed under per- North.Holland Publish#Tg Company - A msterdam 163