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Neurotrophin mRNA expression in the developing tooth suggests multiple roles in innervation and organogenesis
Author(s) -
Luukko Keijo,
Arumäe Urmas,
Karavanov Alexander,
Moshnyakov Maxim,
Sainio Kirsi,
Sariola Hannu,
Saarma Mart,
Thesleff Irma
Publication year - 1997
Publication title -
developmental dynamics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.634
H-Index - 141
eISSN - 1097-0177
pISSN - 1058-8388
DOI - 10.1002/(sici)1097-0177(199710)210:2<117::aid-aja5>3.0.co;2-j
Subject(s) - neurotrophin , biology , dental papilla , nerve growth factor , trigeminal ganglion , neurotrophin 3 , neurite , neurotrophic factors , microbiology and biotechnology , geniculate ganglion , axon , trk receptor , neuroscience , brain derived neurotrophic factor , receptor , pathology , odontoblast , genetics , sensory system , medicine , palsy , alternative medicine , dentin , in vitro
To analyze the roles of neurotrophins during early development of rat teeth, we studied the expression of neurotrophin mRNAs from the initiation of first molar formation to the completion of crown morphogenesis. With RNAase protection assay all neurotrophin mRNAs were detected in embryonic teeth. In situ hybridization analysis revealed developmentally changing, distinct expression patterns for nerve growth factor (NGF) and neurotrophin‐3 (NT‐3), which were shown not to be regulated by or dependent on peripheral innervation. NGF mRNAs appeared in the mesenchymal target field of the tooth at the time of the trigeminal axon ingrowth (embryonic days 14–15: E14–E15), and they were also present along the pathway taken by growing trigeminal axons. NT‐4/5 mRNAs were uniformly expressed in all epithelial cells, but brain‐derived neurotrophic factor (BDNF) transcripts were not detected. All neurotrophins induced neurite outgrowth from E13–E16 trigeminal ganglion explants. These results suggest that NGF is involved in the guidance of trigeminal axons to embryonic teeth. In postnatal teeth, expression of NGF mRNAs, but not other neurotrophins, correlated with trigeminal axon ingrowth, proposing that NGF is involved in local sprouting and establishment of the final innervation pattern of the dental papilla and dentin. These results suggest that NGF is required for tooth innervation and that other neurotrophins may also have regulatory roles. In addition, the expression patterns of NGF, NT‐3, and NT‐4/5 as well as of neurotrophin receptors suggest that the neurotrophin system may also serve non‐neuronal functions during tooth development. Dev. Dyn. 1997;210: 117–129. © 1997 Wiley‐Liss, Inc.