Distinct BMP-Smad signaling outputs confer diverse functions in dental mesenchyme

The canonical bone morphogenetic protein (BMP) signaling pathway plays a crucial regulatory role in tooth development by activating Smad proteins to regulate gene expression. We previously identified an atypical canonical BMP signaling in dental mesenchyme that is Smad4-independent but Smad1/5-dependent. This study demonstrates that phosphorylated Smad1/5 (pSmad1/5) and Smad4 regulate distinct gene sets in murine dental mesenchyme. Real-time monitoring of BMP-Smad transcriptional activity revealed that Smad4-dependent canonical BMP signaling is restricted to neurovascular cells surrounding the condensed dental mesenchymal cells where pSmad1/5 is present. Notably, pSmad1/5 in dental mesenchymal cells form complexes with pSmad3 to prevent canonical BMP signaling. CUT&RUN assays revealed genome-wide co-occupancy of pSmad1/5 and pSmad3, indicating their function as transcriptional regulation units. Integrative analyses demonstrated that this atypical canonical BMP signaling regulates tooth sensory innervation and maintains odontogenic inductive potential in dental mesenchyme, enabling the identification of crucial genes for maintaining tooth inductive capability. Our findings elucidate the operating mechanism of atypical canonical BMP signaling in dental mesenchymal cells and clarify how BMP-Smad signaling exerts diverse functions across different cell types, informing future tooth bioengineering strategies.