Snail Regulates MyoD Binding-Site Occupancy to Direct Enhancer Switching and Differentiation-Specific Transcription in Myogenesis

Abstract

SUMMARY In skeletal myogenesis, the transcription factor MyoD activates distinct transcriptional programs in progenitors compared to terminally differentiated cells. Using ChIP-Seq and gene expression analyses, we show that in primary myoblasts, Snail-HDAC1/2 repressive complex binds and excludes MyoD from its targets. Notably, Snail binds E box motifs that are G/C rich in their central dinucleotides, and such sites are almost exclusively associated with genes expressed during differentiation. By contrast, Snail does not bind the A/T-rich E boxes associated with MyoD targets in myoblasts. Thus, Snai1-HDAC1/2 prevent MyoD occupancy on differentiation-specific regulatory elements, and the change from Snail to MyoD binding often results in enhancer switching during differentiation. Furthermore, we show that a regulatory network involving myogenic regulatory factors (MRFs), Snai1/2, miR-30a, and miR-206 acts as a molecular switch that controls entry into myogenic differentiation. Together, these results reveal a regulatory paradigm that directs distinct gene expression programs in progenitors versus terminally differentiated cells.

Genome-wide identification of enhancers in skeletal muscle: the role of MyoD1

“…These studies dramatically extend previous work in which MyoD1-binding sites were discovered genomewide (Blais et al 2005;Cao et al 2010). More recently, Soleimani et al (2012) identified a set of MyoD1-bound peaks, a substantial number of which were intergenic and ;5600 of which overlapped with Cao et al (2010). Overall, we found that while the majority of MyoD1-binding sites is located within gene-associated or previously uncharacterized intergenic regions (Cao et al 2010), only ;10% of all MyoD1-binding sites were located within active muscle enhancers (in both myoblasts and myotubes), suggesting that there is highly selective binding of MyoD1 to chromatin at transcriptional enhancing regions.…”

Ebf factors and MyoD cooperate to regulate muscle relaxation via Atp2a1

“…Ebf3 was inserted into the mammalian expression vector pCMV cyto using standard methods. CTAP-MyoD was obtained from Michael Rudnicki (University of Ottawa, Canada) as described 39 . PCR using specific primer for genes or genomic DNA were designed with additional restriction sites as indicated below with italic letters.…”

“…MyoD and Myf5 are two bHLH transcription factors binding to E-boxes that are important for myogenic differentiation. ChIP-seq analysis for both factors during proliferation and differentiation of primary myoblasts has been reported and reveals that MyoD binds to two sites in the Atp2a1 promoter during myoblast differentiation, whereas Myf5 does not bind under both conditions 39 . We examined binding of MyoD to E-boxes present in the Atp2a1 promoter by ChIP and could confirm strong binding to site X1 and weaker but sigificant binding also to site X5.…”

A KAP1 phosphorylation switch controls MyoD function during skeletal muscle differentiation

“…How these multiple interactions are regulated and how MyoD-dependent gene targets are defined are still incompletely understood. In muscle precursor cells, MyoD indeed binds as a heterodimer with ubiquitously expressed E proteins to thousands of genomic sites containing a so-called E-box sequence (CAGSTG) (Cao et al 2010;Soleimani et al 2012). However, only a fraction of the genes situated nearby are activated during myotube differentiation (Cao et al 2010).…”