Distinct BMP-Smad Signaling Outputs Confer Diverse Functions in Dental Mesenchyme

Abstract

The canonical bone morphogenetic protein (BMP) signaling pathway plays a crucial regulatory role in tooth development by activating Smad proteins to regulate gene expression. Our previous research 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 transcriptionally regulate distinct gene sets in 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, we found that 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 that pSmad1/5-pSmad3 complexes function as transcriptional regulation units. Integrative analyses of their transcriptional targets with RNA-seq demonstrated that the atypical canonical BMP signaling regulates tooth sensory innervation and is temporally required for maintaining odontogenic inductive potential in the dental mesenchyme. This enabled the identification of potentially critical 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, shedding light on future tooth bioengineering strategies.