The Scaffold attachment factor b1 (Safb1) regulates myogenic differentiation by facilitating the transition of myogenic gene chromatin from a repressed to an activated state

Abstract

The regulation of skeletal muscle gene expression during myogenesis is mediated by lineage-specific transcription factors in combination with numerous cofactors, many of which modify chromatin structure. However, the involvement of scaffolding proteins that organize chromatin and chromatin-associated regulatory proteins has not extensively been explored in myogenic differentiation. Here, we report that Scaffold attachment factor b1 (Safb1), primarily associated with transcriptional repression, functions as a positive regulator of myogenic differentiation. Knockdown of Safb1 inhibited skeletal muscle marker gene expression and differentiation in cultured C2C12 myoblasts. In contrast, over-expression resulted in the premature expression of critical muscle structural proteins and formation of enlarged thickened myotubes. Safb1 co-immunoprecipitated with MyoD and was co-localized on myogenic promoters. Upon Safb1 knockdown, the repressive H3K27me3 histone mark and binding of the Polycomb histone methyltransferase Ezh2 persisted at differentiation-dependent gene promoters. In contrast, the appearance of histone marks and regulators associated with myogenic gene activation, such as myogenin and the SWI/SNF chromatin remodelling enzyme ATPase, Brg1, was blocked. These results indicate that the scaffold protein Safb1 contributes to the activation of skeletal muscle gene expression during myogenic differentiation by facilitating the transition of promoter sequences from a repressive chromatin structure to one that is transcriptionally permissive.

Brg1 Controls the Expression of Pax7 to Promote Viability and Proliferation of Mouse Primary Myoblasts

“…Chromatin immunoprecipitation (ChIP) assays using cultured mouse primary myoblasts were performed in triplicate from three independent biological samples as described by Dacwag et al () and Hernandez‐Hernandez et al (). Proliferating cell lysates were incubated overnight with polyclonal rabbit antisera against Brg1 (De la Serna et al, ), or normal rabbit IgG (Santa Cruz Biotechnology, sc‐3888).…”

The increasing diversity of functions attributed to the SAFB family of RNA-/DNA-binding proteins

“…For example, SAFB1 functions as a positive regulator of myogenic differentiation, with knockdown of SAFB1 inhibiting the expression of skeletal muscle genes [82]. In this case, interaction with the polycomb PRC2 complex was suggested by the persistence of the Ezh2 component of PRC2 and the repressive histone marker H3K27me3 after SAFB1 knockdown.…”

Analysis of polymorphisms in the equine MSTN gene in Polish populations of horse breeds

“…A study performed on sheep myostatin promoter region showed that the MTBF motif was influential on the transcriptional regulation activity and might play a role in the myostatin gene transcription (Du et al, 2007) alongside with OCT1 (Lakich et al, 1998). The g.66495696T 4C polymorphism changed complementarity of the sequence binding of SATB1 (special AT-rich sequence-binding protein 1) associated with chromatin and the nuclear matrix (De Belle et al, 1998) and also act as co-activator of myogenic genes during myogenic differentiation (Hernández-Hernández et al, 2013). The TATA binding protein factor (VTATA-TBP) together with TATA associated factors (TAF) are components of core promoter T T T C T 0 .…”