REGULATION OF RIBOSOMAL-RNA GENE-TRANSCRIPTION DURING RETINOIC ACID-INDUCED DIFFERENTIATION OF MOUSE TERATOCARCINOMA CELLS

We have examined the mechanism of regulation of rRNA synthesis in mous e F9 teratocarcinoma cells that were induced to differentiate by retin oic acid and dibutyryl cAMP. Ribosomal RNA (rRNA) synthesis was signif icantly reduced during differentiation of F9 cells into parietal endod erm cells. Nuclear run-on assay revealed that the rRNA gene transcript ion rates were reduced in differentiated cells, and this phenomenon co uld be mimicked by in vitro transcription assay using nuclear extracts prepared from F9 stem and F9 parietal endoderm cells. Analysis of the DNA-binding activities of two RNA polymerase I (pol I) transcription factors E(1)BF/Ku and UBF revealed decreased affinity for their cognat e recognition sequences. Immunoblot analysis showed a marked reduction in the amounts of E(1)BF/Ku and UBF in the differentiated cells. Anal ysis of the steady-state RNA levels for the smaller subunit of E(1)BF/ Ku and for UBF in differentiating F9 cells revealed decreased mRNA syn thesis and increase in message level for the differentiation-specific marker laminin B1 with progression of the differentiated status of the cells. This study has demonstrated that differentiation of mouse F9 t eratocarcinoma cells into parietal endoderm cells leads to diminished rRNA synthesis, which may be mediated by reduced DNA-binding activitie s and amounts of at least two pol I transcription factors. (C) 1997 Ac ademic Press.