Monitoring of canonical BMP and Wnt activities during postnatal stages of mouse first molar root formation

Jia Wang,Shujun Ran,Bin Liu,Shensheng Gu

doi:10.1590/1678-7757-2021-0281

Abstract

Objective This study aimed to explore the precise temporospatial distributions of bone morphogenetic protein (BMP) and Wnt signaling pathways during postnatal development of mammalian tooth roots after the termination of crown morphogenesis.Methodology A total of two transgenic mouse lines, BRE-LacZ mice and BAT-gal mice, were undertaken. The mice were sacrificed on every postnatal (PN) day from PN 3d up to PN 21d. Then, the first lower molars were extracted, and the dissected mandibles were stained with 5-bromo-4-chloro-3-indolyl-β-d-galactopyranoside (X-gal) and fixed. Serial sections at 10 µm were prepared after decalcification, dehydration, and embedding in paraffin.Results We observed BMP/Smads and Wnt/β-catenin signaling activities in the dental sac, dental pulp, and apical papilla with a certain degree of variation. The position of activation of the BMP/Smad signaling pathway was located more coronally in the early stage, which then gradually expanded as root elongation proceeded and was associated with blood vessels in the pulp and developing complex apical tissues in the later stage. However, Wnt/β-catenin signaling was highly concentrated in the mesenchyme below the cusps in the early stage, gradually expanded to regions around the root in the transition/root stage, and then disappeared entirely in the later stage.Conclusions These results further confirmed the participation of both BMP and Wnt canonical signaling pathways in tooth root development, as well as formed the basis for future studies on how precisely integrated signaling pathways regulate root morphogenesis and regeneration.

Highlights

The outer enamel epithelium is confluent with the inner enamel epithelium at the cervical loop, as well as grows in the apical direction forming the bilayer of an epithelial extension called Hertwig’s epithelial root sheath (HERS), a transient structure that occurs before the complete formation of the tooth root
This study aimed to investigate postnatal M1 morphogenesis before eruption associated with active bone morphogenetic protein (BMP) and Wnt signaling distribution, matching with root development and odontogenesis
The results showed that M1 crown development was completed on postnatal day 3 (PN3) (Figures 1A, 2A) and root development began

Summary

Introduction

Analogous to the ectodermal organogenesis, a series of reciprocal and sequential epithelialmesenchymal interactions are essential for tooth root development, which occurs after crown formation. Multiple signaling cascades have implicated in these processes to guide root development in different stages. The outer enamel epithelium is confluent with the inner enamel epithelium at the cervical loop, as well as grows in the apical direction forming the bilayer of an epithelial extension called Hertwig’s epithelial root sheath (HERS), a transient structure that occurs before the complete formation of the tooth root. The formed HERS extends apically and envelops the dental papilla to form a barrier separating from the dental sac. Analogous to the ectodermal organogenesis, a series of reciprocal and sequential epithelialmesenchymal interactions are essential for tooth root development, which occurs after crown formation.. Multiple signaling cascades have implicated in these processes to guide root development in different stages.. The outer enamel epithelium is confluent with the inner enamel epithelium at the cervical loop, as well as grows in the apical direction forming the bilayer of an epithelial extension called Hertwig’s epithelial root sheath (HERS), a transient structure that occurs before the complete formation of the tooth root.. HERS disintegration orchestrates the deposition of root dentin, which subsequently initiates dental sac cell cementogenesis onto the dentin surface.. HERS disintegration orchestrates the deposition of root dentin, which subsequently initiates dental sac cell cementogenesis onto the dentin surface.4,5 It may participate in cementum formation via epithelial-mesenchymal transition.. HERS disintegration orchestrates the deposition of root dentin, which subsequently initiates dental sac cell cementogenesis onto the dentin surface. it may participate in cementum formation via epithelial-mesenchymal transition. HERS plays a vital role in root development

Methods

Results

Discussion

Conclusion