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

Abstract

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.

Associations between C-section and hand grip strength: an observational analysis and genome-wide environmental interaction study

“…POLR3G gene and WASL gene showed significant G×E interaction effects on left grip strength while CRPPA gene and APBB2 gene showed significant G×E interaction effects on right grip strength. POLR3G participants in the transcription of RNA polymerase III (Pol III) and express in the skeletal muscle cell lineage, which results in a significant reduction in the activation of muscle genes 41 . In addition, the POLR3G overexpression had some ability to reverse differentiation 41 .…”

“…POLR3G participants in the transcription of RNA polymerase III (Pol III) and express in the skeletal muscle cell lineage, which results in a significant reduction in the activation of muscle genes 41 . In addition, the POLR3G overexpression had some ability to reverse differentiation 41 . WASL gene encodes a member of the Wiskott-Aldrich syndrome (WAS) protein family named N-WASP, which is expressed ubiquitously 42 .…”

MAF1, a repressor of RNA polymerase III-dependent transcription, regulates bone mass

“…Two RNA pol III isoforms are differentially expressed between pluripotent and differentiated embryonic stem cells (ESCs) ( Haurie et al, 2010 ; Wong et al, 2011 ; Wang et al, 2020 ). RNA pol III-dependent transcription also modulates the formation of hematopoietic lineages in zebrafish ( Wei et al, 2016 ) and transcription is downregulated during skeletal muscle differentiation of Xenopus tropicalis ( McQueen et al, 2019 ). MAF1 enhances the formation of mesoderm in embryonic stem cells, and the downregulation of RNA pol III-dependent transcription enhances the differentiation of ESCs and 3T3-L1 cells into adipocytes ( Chen et al, 2018 ).…”

Maf1, a repressor of RNA polymerase III-dependent transcription, regulates bone mass

“…Two RNA pol III isoforms are differentially expressed between pluripotent and differentiated embryonic stem cells (ESCs) (24)(25)(26). RNA pol III-dependent transcription also modulates the formation of hematopoietic lineages in zebrafish (27) and transcription is downregulated during skeletal muscle differentiation of Xenopus tropicalis (28). Maf1 enhances the formation of mesoderm in embryonic stem cells, and the downregulation of RNA pol III-dependent transcription enhances the differentiation of ESCs and 3T3-L1 cells into adipocytes (29).…”