Mesodermal FGF and BMP govern the sequential stages of zebrafish thyroid specification

Area of Science:

• Developmental biology
• Endocrinology
• Genetics

Background:

• Thyroid hormone biosynthesis is crucial for development.
• Congenital thyroid diseases often stem from developmental defects.
• Thyroid precursor specification involves FGF and BMP signaling, but their interplay with transcription factors is unclear.

Purpose of the Study:

• To elucidate the interplay between FGF/BMP signaling and transcription factors during thyroid progenitor specification.
• To establish a refined model for thyroid cell specification.
• To investigate the evolutionary conservation of these mechanisms.

Main Methods:

• Analysis of Pax2a and Nkx2.4b expression dynamics in zebrafish embryos.
• Monitoring endodermal FGF and BMP signaling activities.
• Timed manipulation of FGF/BMP signaling pathways.
• Comparative analysis of Pax8 and Nkx2-1 expression in mouse embryos.

Main Results:

• A Pax2a-expressing thyroid progenitor population with high FGF signaling and low BMP/Nkx2.4b signaling was identified.
• Upregulated BMP signaling induced differentiation into lineage-committed precursors co-expressing Pax2a and Nkx2.4b.
• FGF signaling primarily regulates Pax2a, while BMP signaling regulates both Pax2a and Nkx2.4b.
• Similar expression dynamics observed for Pax8 and Nkx2-1 in mouse embryos.

Conclusions:

• A refined model of thyroid cell specification involving sequential regulation by FGF and BMP signaling is proposed.
• This model highlights the distinct roles of FGF and BMP in regulating key transcription factors.
• The findings suggest evolutionary conservation of thyroid cell specification mechanisms from zebrafish to mammals.