Molecular characterization of young and mature odontoblasts.
The odontoblast is the secretory cell responsible for primary, secondary and tertiary reactionary dentinogenesis. We provide evidence that the changes in secretory activity of odontoblasts reflect differential transcriptional control and that common regulatory processes may exist between dentine and bone.


BACKGROUND
Based on the hypothesis that differential dentine secretion (primary and secondary dentinogenesis) is associated with changes in the transcriptional control within the cell, we have investigated the transcriptome of odontoblasts at young and mature stages and subsequently used this information to identify key regulatory intracellular pathways involved in this process.


METHODS
We used microarray analysis to compare the transcriptome of early stage (primary dentinogenesis) and late stage (secondary dentinogenesis) odontoblasts from 30 month old bovine teeth. Secondarily, we used post-array sqRT-PCR to confirm the differential expression of 23 genes in both populations of odontoblasts. Finally, immunohistochemistry was performed on bovine and murine tissues with antibodies to DMP1 and anti-phospho p38 proteins.


RESULTS
DMP-1 and osteocalcin gene expression were up-regulated in the mature odontoblasts, whereas collagen I, DSPP, TGF-beta1 and TGF-beta1R gene expression were down-regulated. Microarray analysis highlighted 574 differentially regulated genes (fold change>2 - p<0.05). This study supports further existing similarities between pulp cells and bone cells. Using post-array Sq-RT-PCR we characterized transcript levels of genes involved in the p38 MAP kinase pathway (PTPRR, NTRKK2, MAPK13, MAP2K6, MKK3). Differential p38 gene activation was confirmed by immunohistochemistry for p38 protein in murine teeth. Finally, immunohistochemistry for DMP1 indicated that odontoblasts involved in primary and secondary dentinogenesis may coexist in the same tooth.


CONCLUSIONS
As established in bone cells, the transcriptome of the odontoblast was shown here to evolve with their stage and functional maturity. Identification of the involved signalling pathways, as highlighted for p38, will enable the deciphering of physiology and pathology of mineralised tissue formation.
Simon
S
S
INSERM, UMR S 872, Centre de Recherche des Cordeliers, Paris, France. srs635@bham.ac.uk
Smith
A J
AJ
Lumley
P J
PJ
Berdal
A
A
Smith
G
G
Finney
S
S
Cooper
P R
PR
D000818:Animals; D002417:Cattle; D016922:Cellular Senescence; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D007150:Immunohistochemistry; D007180:Incisor / Q000166:cytology / Q000378:metabolism; D051379:Mice; D009804:Odontoblasts / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D012313:RNA / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014078:Tooth Eruption / Q000235:genetics; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D010750:Phosphoproteins; D012313:RNA; D048051:p38 Mitogen-Activated Protein Kinases