Spatial and temporal coordination of signaling pathways in tissue differentiation: Developmental atlas of protein expression during zebra finch beak maturation

BACKGROUND: Morphogenesis depends on spatial and temporal coordination of signaling pathways, yet context-specificity in interactions among these pathways during cartilage and bone differentiation remains poorly understood. Here we map cellular and histological localization of regulatory proteins forming core craniofacial developmental pathways of the zebra finch (Taeniopygia guttata) to provide insight into their functional roles during beak morphogenesis. RESULTS: We present an atlas of spatiotemporal coexpression of β-catenin, Bmp4, CaM, Dkk3, Fgf8, Ihh, Tgfβ2, and Wnt4 across embryonic stages HH29-42. Early stages (HH29-32), showed broad expression across epithelial and mesenchymal tissues, followed by progressive compartmentalization by HH36, with pronounced divergence among tissues. Notably, at later stages, proteins showed tissue-specific distributions in boundary versus core regions of chondrogenic and osteogenic domains, indicating coordinated cross-pathway patterning during cartilage and bone formation. CONCLUSIONS: We find that osteogenesis in the zebra finch beak is organized by coordinated signaling between boundary-associated cells and differentiating cores; cross-pathway feedback establishes bone and cartilage differentiation while maintaining boundaries. Our results corroborate core aspects of craniofacial signaling dynamics and yet reveal unexpected subcellular localization of some key proteins identifying regulatory complexity not captured by prior transcript-level maps. This atlas provides a protein-level baseline for comparative and mechanistic studies of avian beak morphogenesis.