Thyroid hormone induces constitutive keratin gene expression during Xenopus laevis development

Area of Science:

• Developmental Biology
• Molecular Endocrinology
• Amphibian Metamorphosis

Background:

• Thyroid hormone (T3) is crucial for amphibian metamorphosis.
• Keratin gene expression changes significantly during Xenopus laevis development.
• Previous studies indicated a two-step activation process for 63-kDa keratin genes in vivo.

Purpose of the Study:

• To investigate the role of T3 in activating 63-kDa keratin genes in vitro.
• To characterize the T3-dependent step in keratin gene activation.
• To determine if T3 induces a stable change in epidermal cells.

Main Methods:

• In vitro explant cultures of Xenopus laevis skin.
• Addition of T3 to skin cultures at different developmental stages.
• Measurement of keratin mRNA concentration over time.
• Analysis of gene transcription and expression levels.

Main Results:

• The activation of 63-kDa keratin genes in vitro requires two steps, similar to in vivo.
• A significant latent period of approximately 2 days exists between T3 addition and increased keratin mRNA.
• Transient T3 exposure at stage 40 leads to high-level gene expression at stage 48, even without continuous T3.
• Induced genes are stably expressed, and T3 has no further effect by the end of metamorphosis.

Conclusions:

• T3 induces a stable, long-term change in epidermal cells, enabling later expression of 63-kDa keratin genes.
• This T3-induced change can persist through significant cell proliferation and development.
• T3 initiates constitutive expression of 63-kDa keratin genes during metamorphosis.