Sonic hedgehog signalling from foregut endoderm patterns the avian nasal capsule

Area of Science:

• Developmental Biology
• Craniofacial Development
• Molecular Biology

Background:

• Facial skeleton morphogenesis relies on inductive interactions between cephalic neural crest cells and epithelia.
• The foregut endoderm plays a role in these crucial developmental signaling pathways.

Purpose of the Study:

• To investigate the role of endoderm zone I (EZ-I) and its Sonic hedgehog (Shh) expression in avian nasal capsule formation.
• To elucidate the signaling mechanisms underlying facial morphogenesis.

Main Methods:

• Surgical manipulation of EZ-I in avian embryos (ablation and grafting).
• Utilized Shh-loaded beads and Shh signaling inhibitors to assess pathway necessity.
• In vitro co-culture systems to study endoderm-neural crest cell interactions.
• Analyzed Gli1 induction as a marker for Shh pathway activation.

Main Results:

• Removal of EZ-I specifically abolished mesethmoid cartilage formation.
• Addition of supernumerary EZ-I induced ectopic mesethmoid cartilage.
• Shh signaling is necessary and sufficient for mesethmoid development, as demonstrated by rescue experiments and pathway inhibition.
• Endoderm-neural crest cell interactions were confirmed in vitro via Gli1 induction.

Conclusions:

• Early endodermal regionalization, specifically Shh signaling from EZ-I, is essential for patterning the ventral nasal capsule.
• Disruption of this endodermal signaling can lead to craniofacial defects, highlighting its importance in embryonic development.
• This study provides critical insights into the molecular basis of facial morphogenesis and potential causes of congenital craniofacial anomalies.