MUNC, a Long Noncoding RNA That Facilitates the Function of MyoD in Skeletal Myogenesis

Abstract

An in silico screen for myogenic long noncoding RNAs (lncRNAs) revealed nine lncRNAs that are upregulated more than 10-fold in myotubes versus levels in myoblasts. One of these lncRNAs, MyoD upstream noncoding (MUNC, also known as DRR eRNA ), is encoded 5 kb upstream of the transcription start site of MyoD, a myogenic transcription factor gene. MUNC is specifically expressed in skeletal muscle and exists as in unspliced and spliced isoforms, and its 5= end overlaps with the cis-acting distal regulatory region (DRR) of MyoD. Small interfering RNA (siRNA) of MUNC reduced myoblast differentiation and specifically reduced the association of MyoD to the DRR enhancer and myogenin promoter but not to another MyoD-dependent enhancer. Stable overexpression of MUNC from a heterologous promoter increased endogenous MyoD, Myogenin, and Myh3 (myosin heavy chain, [MHC] gene) mRNAs but not the cognate proteins, suggesting that MUNC can act in trans to promote gene expression but that this activity does not require an induction of MyoD protein. MUNC also stimulates the transcription of other genes that are not recognized as MyoD-inducible genes. Knockdown of MUNC in vivo impaired murine muscle regeneration, implicating MUNC in primary satellite cell differentiation in the animal. We also discovered a human MUNC that is induced during differentiation of myoblasts and whose knockdown decreases differentiation, suggesting an evolutionarily conserved role of MUNC lncRNA in myogenesis. Although MUNC overlaps with the DRR enhancer, our results suggest that MUNC is not a classic cisacting enhancer RNA (e-RNA) acting exclusively by stimulating the neighboring MyoD gene but more like a promyogenic lncRNA that acts directly or indirectly on multiple promoters to increase myogenic gene expression.

Linc-YY1 promotes myogenic differentiation and muscle regeneration through an interaction with the transcription factor YY1

“…More reports clearly demonstrate that bona fide single-exonic lncRNAs are as functional as multi-exonic ones; therefore, the common practice of omitting single-exonic transcripts to simplify the identification pipeline may lead to an incomplete catalogue of lincRNAs. Despite the rapidly increasing number of lincRNAs functionally investigated so far, research of lincRNA in myogenesis is still at its infancy with a handful being characterized to date 11,[38][39][40] . Our study provides a comprehensive characterization of Linc-YY1 functionally and mechanistically.…”

Non-coding RNAs in muscle differentiation and musculoskeletal disease

“…Enhancer RNAs (eRNAs) have been implicated in myogenesis (Figure 2 (87). In this case, MUNC RNA knockdown had effects on myogenin as well as on MyoD and Myh3 expression, and on other genes that are not known to be induced by MyoD.…”

<i>MyoD</i> is regulated by the miR-29a-<i>Tet1</i> pathway in C2C12 myoblast cells

“…MyoD, which is a myogenesis progressing transcription factor (32), was upregulated by Tet1 inhibition and downregulated by miR-29a inhibition in C2C12 cells mainly at days 1 and 2. MyoD is known to be the target gene of Pax-3, Myf5 and a long non-coding RNA, MUNC (32)(33)(34)(35). However, neither Tet1 nor miR-29 inhibition enhanced the expression of Myf5 in our real-time RT-PCR analysis, and miR-29a inhibition did not upregulate Pax3 in the microarray analysis.…”