Tooth Morphogenesis Flashcards
What tooth type is present in humans but not mice?
Premolars
When is the tooth type determined?
Initiation stage
When does the homeobox code activate in the lower jaw?
6 weeks in utero
What are homeobox genes?
Genes with ‘homeobox domains’ within their sequence which combine to other parts of DNA to control expression of other genes
Where in the dental mesenchyme is Barx1 expressed during the initiation stage?
Molar region
Where in the dental mesenchyme is Msx1 expressed during the initiation stage?
Incisor region
In the shrew, what do the levels of Barx1 determine?
Number of cusps (high levels = more cusps)
What is the function of the homeobox code in the context of teeth?
Decides what tooth (gene) and how complex (level)
In what tissue are homeobox genes expressed?
Dental mesenchyme
When does the PEK appear?
Bud stage
What causes the formation of the PEK?
Signals from mesenchyme: BMP4 and activin
What do FGF4 and SHH do (PEK)?
Stimulate growth of dental epithelium to form cap shape
What two factors are important in moving from the bud stage to the cap stage?
Juxtaposition of proliferating and non-proliferating cells
Rearrangement of cells (involves focal adhesion kinases)
What happens if focal adhesion kinases are lost?
Cells cannot rearrange in bud so cap stage is not reached
How is the PEK lost?
Apoptosis
What molecule is involved in apoptosis of the EK?
BMP4 (in EK)
What does the number of SEKs determine?
Number of cusps
What does the timing of initiation of SEKs relate to?
Height of the cusps formed
How could you increase cusp number?
Stimulate enamel knot-inducing pathways using activin, EDA, SHH
What makes a tooth more likely to have a cusp of Carabelli?
Larger crown area with more compact cusps
Why might bigger jaws result in larger teeth?
Alveolar bone surrounding tooth can give more space
How does hypohidrotic ectodermal dysplasia affect the teeth?
Reduced number (hypodontia)
Flattened cusps (strange peg-shaped morphology)
Abnormal enamel knot shape
What does ectodysplasin A do in tooth development?
Binds to EDAR in EK to turn on EDARADD (EDAR-associated death domain protein)
What do enamel knots express? (5)
EDAR
FGF4
P21
SHH
WNT10B
