Objectives:
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 of the crown. The aim of this study is to address putative regulatory roles of Sema3A chemorepellant in the development of incisor innervation and formation.
Methods:
We analyzed expression of Sema3A mRNAs during embryonic and early postnatal 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 of incisor tooth germ, they were absent in dental papilla or pulp at later stages. Sema3A mRNAs were also observed in the dental epithelium including the cervical loops and a prominent expression was also seen in alveolar bone. Of note, 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 innervation of mouse incisor. In particular, Sema3A appears to regulate innervation of the periodontal ligament, while nerve penetration into the dental pulp appears not to be dependent on Sema3A. Moreover, it may also regulate cellular functions of the cervical loop cells and the development of the 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.
This study has been supported by grants from the Norwegian Cancer Society and L. Meltzer's foundation.