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Thyroid hormone-induced gene expression program for amphibian tail resorption
1Department of Embryology, Carnegie Institution of Washington, Baltimore, MD 21210.
Abstract:
The changes in gene expression leading to tail resorption that are initiated by thyroid hormone (TH) were studied in Xenopus laevis. Four of the less than 10 genes that are down-regulated during this period have been isolated; their mRNAs decay with identical kinetics. Twenty of the approximately 35 genes that are up-regulated in the first 48 h have been isolated. The up-regulated genes fall into two kinetic patterns. After a lag of several hours, the direct response genes (including thyroid hormone receptor beta) increase their mRNA level steadily for 24-48 h. The delayed genes respond mainly in the second 24 h after TH addition. The importance of these genes for tail resorption is supported by the fact that they are all regulated developmentally during normal metamorphosis in tail and respond to hormone induction when the tail becomes competent to respond to TH. The relatively simple gene expression program leading to tail resorption is contrasted with the complex and multiple periods of gene expression during limb development. The gene expression screen defines the tail resorption program and has isolated the majority of TH-regulated genes.
Insights
Thyroid hormone (TH) initiates gene expression changes for Xenopus laevis tail resorption. Researchers identified most TH-regulated genes, revealing distinct direct and delayed responses crucial for this developmental process.
Area of Science:
- Developmental Biology
- Molecular Endocrinology
- Genomics
Background:
- Thyroid hormone (TH) orchestrates complex developmental processes, including amphibian metamorphosis.
- Tail resorption in Xenopus laevis is a well-established model for studying TH-induced gene regulation.
Purpose of the Study:
- To comprehensively identify and characterize genes regulated by thyroid hormone during Xenopus laevis tail resorption.
- To elucidate the temporal patterns of gene expression changes in response to TH.
Main Methods:
- Gene expression profiling in Xenopus laevis tadpoles treated with thyroid hormone.
- Isolation and kinetic analysis of down-regulated and up-regulated genes.
- Comparison of gene expression patterns with normal tail metamorphosis and limb development.
Main Results:
- Identified the majority of TH-regulated genes involved in tail resorption.
- Observed distinct kinetic patterns for up-regulated genes: direct (early) and delayed responses.
- Down-regulated genes exhibited identical mRNA decay kinetics.
Conclusions:
- The tail resorption gene expression program is relatively simple compared to other developmental processes like limb development.
- Identified genes are developmentally regulated and respond to TH induction, confirming their role in tail resorption.
- This study provides a foundational understanding of the molecular mechanisms driving TH-mediated tail resorption.