<i>NRMLncR,</i> a myocyte-enriched long non-coding RNA, enhances myogenesis in mouse

Myogenesis is a stepwise process encompassing myogenic progenitor proliferation, lineage commitment, differentiation, myocyte fusion, and myotube maturation, and it is orchestrated by myogenic regulatory factors (MRFs) together with signaling pathways that coordinate these transitions. Long noncoding RNAs (lncRNAs) have emerged as important regulators of muscle development and regeneration, yet how lncRNAs integrate with canonical signaling networks to shape myogenic progression remains incompletely defined. Here, we identify a novel myocyte-enriched, Notch-repressed myogenic lncRNA (<i>NRMLncR,</i> known as <i>A930003A15Rik</i>), as a previously uncharacterized regulator of mouse myogenesis. The expression of <i>NRMLncR</i> is robustly induced during primary myoblast activation and differentiation. Loss-of-function analyses show that knockdown of <i>NRMLncR</i> impairs myogenic differentiation, accompanied by reduced expression of key myogenic genes. In contrast, adenovirus-mediated overexpression of <i>NRMLncR</i> enhances myogenic differentiation <i>in vitro</i> and is associated with increased muscle fiber size <i>in vivo</i>. Mechanistically, MyoD and MyoG occupy the <i>NRMLncR</i> promoter and promote its transcription during myogenic differentiation. <i>NRMLncR</i> knockdown alerts the transcription of nearby genes, suggesting its function through a cis-regulatory mechanism. RNA pull-down assays further identify an interaction between <i>NRMLncR</i> and the RNA-binding protein CELF1. Together, these findings establish <i>NRMLncR</i> as a novel Notch-associated lncRNA that promotes myogenic differentiation and provide insight into lncRNA-dependent regulation of the myogenic program.