Skeletal muscle differentiation drives a dramatic downregulation of RNA polymerase III activity and differential expression of Polr3g isoforms

• Published in: Developmental biology 2019-10, Vol.454 (1), p.74-84
• Main Authors: McQueen, Caitlin, Hughes, Gideon L., Pownall, Mary E.
• Format: Article
• Language: English
• Subjects: Animals; Cell Differentiation - genetics; Gene Expression Regulation, Developmental; Gene Regulatory Networks; Muscle Development; Muscle, Skeletal - embryology; Muscle, Skeletal - metabolism; Promoter Regions, Genetic; Protein Isoforms; Protein Subunits - metabolism; RNA Polymerase III - genetics; RNA Polymerase III - metabolism; RNA, Messenger - genetics; RNA, Messenger - metabolism; TATA-Binding Protein Associated Factors - metabolism; Transcription, Genetic; Transcriptome; Xenopus; Xenopus Proteins - genetics; Xenopus Proteins - metabolism
• ISSN: 0012-1606; 1095-564X
• DOI: 10.1016/j.ydbio.2019.06.001

Gene regulatory networks underpinning skeletal muscle determination and differentiation have been extensively investigated, providing molecular insights into how cell lineages are established during development. These studies have exclusively focused on the transcriptome downstream of RNA polymerase II (Pol II). RNA polymerase III (Pol III) drives the production of tRNAs and other small RNAs essential for the flow of genetic information from gene to protein and we have found that a specific isoform of a subunit unique to Pol III is expressed early in the myogenic lineage. This points to the possibility that additional regulatory networks exist to control the production of Pol III transcripts during skeletal muscle differentiation. We describe the differential expression of Polr3g and its alternate isoform Polr3gL during embryonic development and using a custom tRNA microarray, we demonstrate their distinct activity on the synthesis of tRNA isoacceptors. We show that Pol III dependent transcripts are dramatically down-regulated during the differentiation of skeletal muscle, as are mRNAs coding for Pol III associated proteins Brf1 and Brf2, while Polr3gL is up-regulated alongside contractile protein genes. Forcing Polr3g expression in this context results in a partial reversal of myogenic differentiation. •There are 2 distinct isoforms of Pol III with either the subunit Polr3g or Polr3gL.•Polr3g and Polr3gL have complementary expression during development.•Polr3g is transiently expressed in early somites; Polr3gL is activated later.•Pol III activity decreases during differentiation, while Polr3gL increases.•Expression of Polr3g is not compatible with differentiation.