Is thyroid hormone signaling relevant for vertebrate embryogenesis?

Area of Science:

• Developmental Biology
• Endocrinology
• Molecular Biology

Background:

• Thyroid hormones (THs) traditionally linked to postembryonic development (e.g., metamorphosis).
• Embryonic development's role in TH physiology received less attention.
• Prevailing concepts: low embryonic TH levels, TRs expressed, aporeceptor represses transcription without TH.

Purpose of the Study:

• Revisit concepts of TH physiology during embryonic development.
• Investigate TH availability in eggs and embryos.
• Explore the complex control of transcription by TRs and THs.

Main Methods:

• Review of accumulating data on TH availability.
• Analysis of emerging knowledge on TR and TH transcriptional control.
• Comparative analysis across species (amphibians, mammals).

Main Results:

• Data suggests THs play a role earlier than previously thought.
• Embryonic TH availability and TR/TH transcriptional control are more complex than models indicate.
• Existing concepts may need revision based on new findings.

Conclusions:

• THs are important throughout development, including embryonic stages.
• The interplay between TRs and THs in gene regulation is intricate.
• Further research is needed to fully elucidate TH roles in early development.