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Polarizing activity, Sonic hedgehog, and tooth development in embryonic and postnatal mouse
1Department of Anatomy and Histology, School of Dental Medicine, University of Pennsylvania, Philadelphia 19104, USA.
Summary
Tooth germs exhibit polarizing activity, similar to developing limbs, inducing extra digits and expressing key developmental genes like Sonic hedgehog (Shh). This activity is crucial for tooth morphogenesis and is concentrated in specific regions during development.
Area of Science:
- Developmental Biology
- Oral Biology
- Regenerative Medicine
Background:
- Tooth development shares similarities with limb morphogenesis, involving complex epithelial-mesenchymal interactions.
- Investigating conserved morphogenetic signals between these systems can reveal fundamental developmental mechanisms.
Purpose of the Study:
- To determine if developing tooth germs possess polarizing activity, analogous to limb development.
- To identify molecular signals, such as Sonic hedgehog (Shh), involved in tooth morphogenesis.
Main Methods:
- Grafting mouse embryo tooth germs onto chick embryo wing buds to assess polarizing activity.
- In situ hybridization and immunohistochemistry to detect gene and protein expression (Hoxd-12, Hoxd-13, Shh).
Main Results:
- Tooth germ grafts induced supernumerary digits in host wing buds, confirming polarizing activity.
- Polarizing activity varied with developmental stage, peaking at late bell stage, and showed a proximo-distal gradient in incisors.
- Tooth germs express Sonic hedgehog (Shh), particularly in the enamel knot and differentiating ameloblasts, and induce Hoxd gene expression.
Conclusions:
- Developing tooth germs possess significant polarizing activity, mediated by factors like Shh.
- These signals play critical roles in establishing polarity and regulating morphogenesis during tooth development.
- Shh is likely involved in cytogenetic events during odontogenesis, particularly with differentiating ameloblasts.