Developmentally regulated expression of Sema3A chemorepellant in the developing mouse incisor

Abstract

Objective. Semaphorin 3A (Sema3A) is an essential chemorepellant controlling peripheral axon pathfinding and patterning, but also serves non-neuronal cellular functions. Incisors of rodent are distinctive from molars as they erupt continuously, have only one root and enamel is present only on the labial side. The aim of this study is to address putative regulatory roles of Sema3A chemorepellant in the development of incisor innervation and formation. Materials and methods. This study analyzed expression of Sema3A mRNAs during embryonic and early post-natal stages of mouse mandibular incisor using sectional radioactive in situ hybridization. Results. Although Sema3A mRNAs were observed in condensed dental mesenchyme during the early bud stage, they were absent in dental papilla or pulp at later stages. Sema3A mRNAs were observed in the dental epithelium including the cervical loops and a prominent expression was also seen in alveolar bone. Interestingly, transcripts were absent from the mesenchymal dental follicle target area (future periodontal ligament) throughout the studied stages. Conclusion. The expression patterns of Sema3A indicate that it may control the timing and patterning of the incisor innervation. In particular, Sema3A appears to regulate innervation of the periodontal ligament, while nerve penetration into the incisor dental pulp appears not to be dependent on Sema3A. Moreover, Sema3A may regulate the functions of cervical loops and the development of alveolar bone. Future study with Sema3A deficient mice will help to elucidate the putative neuronal and non-neuronal functions of Sema3A in incisor tooth development.

Key Words::

• axon guidance
• incisors
• periodontal ligament
• radioactive in situ hybridization
• Semaphorin 3A

Acknowledgement

Kjellfrid Haukanes is acknowledged for skillful technical assistance. We thank the staff of the animal facility for careful mouse husbandry. This study has been supported by grants from the Norwegian Cancer Society and L. Meltzer's foundation.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.