An essential role for Fgfs in endodermal pouch formation influences later craniofacial skeletal patterning

Area of Science:

• Developmental Biology
• Molecular Biology
• Genetics

Background:

• Fibroblast growth factors (Fgfs) regulate pharyngeal arch development.
• Previous studies in chick and mouse (Fgf8) and zebrafish (Fgf3) highlighted Fgf roles in neural crest cell differentiation and survival.
• The precise function of Fgfs in early pharyngeal endoderm segmentation remained unclear.

Purpose of the Study:

• To investigate the role of Fgf8 and Fgf3 in early pharyngeal endoderm segmentation in zebrafish.
• To determine the necessity of Fgf signaling for pharyngeal pouch formation and subsequent cartilage development.

Main Methods:

• Time-lapse microscopy to observe pharyngeal pouch formation.
• Gene knockdown (doubly reduced Fgf8 and Fgf3) to assess functional requirements.
• Cell transplantation and pharmacological treatments.
• Analysis of pharyngeal cartilage development.

Main Results:

• Pharyngeal pouches form through directed lateral migration of endodermal cell clusters.
• Doubly reduced Fgf8 and Fgf3 led to disorganized cell migration and failed pouch formation.
• Fgf8 and Fgf3 are required in the neural keel and cranial mesoderm for early pouch formation.
• Severe reductions in hyoid and branchial cartilages were observed in Fgf-deficient embryos.
• Pouch structure defects correlated with later cartilage defects.

Conclusions:

• Fgf8 and Fgf3 signaling in the mesoderm and hindbrain organizes pharyngeal endoderm segmentation into pouches.
• Fgf-dependent pharyngeal endoderm morphogenesis is critical for the patterning of pharyngeal cartilages.
• This study reveals an essential, early role for Fgf signaling in pharyngeal development.