Conversion of MyoD to a Neurogenic Factor: Binding Site Specificity Determines Lineage

• Mutations that redirect MyoD to NeuroD2 binding sites make it a neurogenic factor
• A MyoD chimera with a NeuroD2 bHLH domain redirects MyoD to NeuroD2 E-boxes
• Mutation of the MyoD PBX interacting residues is necessary to lose myogenic activity
• The lineage determined by a master regulatory factor can be rationally reprogrammed

SummaryMyoD and NeuroD2, master regulators of myogenesis and neurogenesis, bind to a “shared” E-box sequence (CAGCTG) and a “private” sequence (CAGGTG or CAGATG, respectively). To determine whether private-site recognition is sufficient to confer lineage specification, we generated a MyoD mutant with the DNA-binding specificity of NeuroD2. This chimeric mutant gained binding to NeuroD2 private sites but maintained binding to a subset of MyoD-specific sites, activating part of both the muscle and neuronal programs. Sequence analysis revealed an enrichment for PBX/MEIS motifs at the subset of MyoD-specific sites bound by the chimera, and point mutations that prevent MyoD interaction with PBX/MEIS converted the chimera to a pure neurogenic factor. Therefore, redirecting MyoD binding from MyoD private sites to NeuroD2 private sites, despite preserved binding to the MyoD/NeuroD2 shared sites, is sufficient to change MyoD from a master regulator of myogenesis to a master regulator of neurogenesis.

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