(a) A proposed hierarchical and regionalized gene regulatory network, summarizing the source and identity of signals that regulate transcription of Bmp2 for downstream specification of Sp7+/Col1A1+ osteoblasts in the periosteal niche. Boxed regions, biological compartments; Boxed text, inputs evaluated in this study; Double arrows in a link, communication across territories; Flat footpads ending at genetic loci, transcriptional inhibition; Pointed footpads ending at genetic loci, transcriptional induction; Diamonds under footpads, evidence of direct cis-regulatory interaction provided by our study; White bubbles, protein/protein interactions. Made with Biotapestry.org.