Top panel, LPMs residing in the peritoneal cavity respond to retinoic acid, which activates primed retinoic acid responsive enhancers. These in turn induce the expression of direct retinoic acid target genes that include transcription factors (e.g., GATA6, RARβ) that collaborate with PU.1 to select and activate LPM-specific enhancers. Lower panel, MG residing in the brain respond to TGFβ, which activates primed SMAD-responsive enhancers. These in turn induced the expression of direct SMAD target genes that include transcription factos (e.g., Mef2b) that collaborate with PU.1 to select and activate MG-specific enhancers.