Tissue-dependent and developmentally regulated cytosolic thyroid-hormone-binding proteins (CTBPs) in Xenopus

Area of Science:

• Developmental Biology
• Molecular Endocrinology
• Comparative Physiology

Background:

• Thyroid hormones regulate metamorphosis in amphibians like Xenopus.
• Cytosolic thyroid-hormone-binding proteins (CTBPs) play a role in mediating thyroid hormone action.
• Understanding the specific CTBPs involved and their regulation is key to deciphering developmental processes.

Purpose of the Study:

• To identify and characterize Xenopus cytosolic thyroid-hormone-binding proteins (CTBPs).
• To investigate the tissue-specific and developmental expression patterns of these CTBPs.
• To determine the binding affinities of CTBPs for thyroid hormones.

Main Methods:

• Photoaffinity labeling to identify CTBPs.
• [125I]T3-binding assays to quantify binding activity.
• Analysis of protein expression across different developmental stages and tissues (liver, head, hindlimb).

Main Results:

• A 59 kDa CTBP, predominant in adult liver, appears at metamorphic climax and persists post-metamorphosis.
• A 38 kDa CTBP is transiently expressed in the head region during metamorphic climax.
• A distinct, non-photoaffinity labeled CTBP is found in hindlimb buds, decreasing with limb growth.
• High-affinity T3 binding sites (Kd 10^-9 to 10^-8 M) were detected in liver, head, and hindlimb cytosol.

Conclusions:

• Xenopus cytosol contains at least three distinct CTBPs.
• These CTBPs exhibit tissue-dependent and developmentally regulated expression patterns.
• The identified CTBPs are likely involved in mediating thyroid hormone effects during Xenopus development and metamorphosis.