Emerin anchors Msx1 and its protein partners at the nuclear periphery to inhibit myogenesis

Abstract

Background Previous studies have shown that in myogenic precursors, the homeoprotein Msx1 and its protein partners, histone methyltransferases and repressive histone marks, tend to be enriched on target myogenic regulatory genes at the nuclear periphery. The nuclear periphery localization of Msx1 and its protein partners is required for Msx1’s function of preventing myogenic precursors from pre-maturation through repressing target myogenic regulatory genes. However, the mechanisms underlying the maintenance of Msx1 and its protein partners’ nuclear periphery localization are unknown. Results We show that an inner nuclear membrane protein, Emerin, performs as an anchor settled at the inner nuclear membrane to keep Msx1 and its protein partners Ezh2, H3K27me3 enriching at the nuclear periphery, and participates in inhibition of myogenesis mediated by Msx1. Msx1 interacts with Emerin both in C2C12 myoblasts and mouse developing limbs, which is the prerequisite for Emerin mediating the precise location of Msx1, Ezh2, and H3K27me3. The deficiency of Emerin in C2C12 myoblasts disturbs the nuclear periphery localization of Msx1, Ezh2, and H3K27me3, directly indicating Emerin functioning as an anchor. Furthermore, Emerin cooperates with Msx1 to repress target myogenic regulatory genes, and assists Msx1 with inhibition of myogenesis. Conclusions Emerin cooperates with Msx1 to inhibit myogenesis through maintaining the nuclear periphery localization of Msx1 and Msx1’s protein partners.

Emerin interacts with histone methyltransferases to regulate repressive chromatin at the nuclear periphery

“…H3K9me2 and H3K27me3 are the products of G9a ( Shinkai and Tachibana, 2011 ) and EZH2 ( Tan et al, 2014 ), respectively, and inhibition of these HMTs disrupts LAD formation ( Towbin et al, 2012 ; Harr et al, 2015 ). The mechanism of HMT recruitment to LADs remains unclear, but HDAC3 was shown to recruit EZH2 to repressive loci ( Wang et al, 2011 ; Zhang et al, 2012 ; Emmett and Lazar, 2019 ) and emerin was shown to recruit EZH2 and H3K27me3 to the nuclear periphery in C2C12 myoblasts and 293T cells ( Ma et al, 2019 ).…”

“…One candidate protein is Msx1. Emerin was shown to bind Msx1 and bridge an interaction between EZH2 and emerin ( Ma et al, 2019 ). G9a was also shown to interact with Msx1 ( Wang and Abate-Shen, 2012a ), so it is possible Msx1 mediates the binding of emerin to HMTs.…”

“…The functional interaction of emerin with EZH2 and Msx1 is important for myogenic differentiation. Emerin knockdown in proliferating C2C12 myoblasts was shown to displace EZH2 and H3K27me3 from the nuclear periphery ( Ma et al, 2019 ), suggesting emerin binding to EZH2 organizes repressive chromatin at the periphery ( Wang and Abate-Shen, 2012b ). Further, the catalytic activity of EZH2 was essential for myogenic differentiation ( Caretti et al, 2004 ).…”

“…Msh homeobox 1 (Msx1) has been shown to colocalize with polycomb repressive complex 2 (PRC2) and H3K27me3 at the nuclear periphery in C2C12 cells and primary myoblasts ( Wang et al, 2011 ). Emerin is responsible for the recruitment of Msx1 and EZH2 to the nuclear envelope ( Ma et al, 2019 ). EZH2, the catalytic component of PRC2, mediates the trimethylation of H3K27 ( Tan et al, 2014 )—a repressive histone modification reported to be enriched in lamina-associated domains ( van Steensel and Belmont, 2017 ).…”

“…ChIP-Seq experiments show H3K27me3 enrichment and repression of transcriptional regulators Myf5 and MyoD is dependent upon Msx1 ( Wang et al, 2011 ). Localization of Msx1 and EZH2 at the nuclear envelope is emerin-dependent, as emerin-knockdown in C2C12 myoblasts caused both Msx1 and EZH2 localization to be lost at the inner nuclear membrane ( Wang and Abate-Shen, 2012b ; Ma et al, 2019 ).…”