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Proceedings of the National Academy of Sciences of the United States of America logoLink to Proceedings of the National Academy of Sciences of the United States of America
. 1993 Sep 1;90(17):7933–7936. doi: 10.1073/pnas.90.17.7933

Coordinated decreases in rRNA gene transcription factors and rRNA synthesis during muscle cell differentiation.

D E Larson 1, W Xie 1, M Glibetic 1, D O'Mahony 1, B H Sells 1, L I Rothblum 1
PMCID: PMC47261  PMID: 8396256

Abstract

rRNA synthesis decreases significantly during the differentiation of rat L6 myoblasts to myotubes. Nuclear run-on assays demonstrated that the decrease was attributable to decreased rates of rRNA gene transcription. Immunoblot analysis indicated a marked reduction in amounts of the RNA polymerase I transcription factors UBF1 and UBF2 (upstream binding factors 1 and 2, respectively). The levels of these factors dropped in parallel with the down-shift in rRNA gene transcription. The amount of UBF does not fall due to a general decrease in cellular protein, as myosin heavy-chain protein accumulates markedly during this same time. RNA blots of total RNA isolated from myoblasts and differentiating myotubes showed a decrease in the mRNA for UBF, at the same time the mRNA for myogenin was accumulating. The down-shift in UBF mRNA levels preceded the decrease in the protein levels for UBF. There have been reports that the acute response of the rRNA gene transcription system to physiological signals in many systems involves an RNA polymerase I-associated factor. However, our results imply that the regulation of rRNA gene DNA transcription in response to physiological processes, such as differentiation, may involve multiple regulatory pathways.

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Selected References

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