The expression pattern of thyroid hormone response genes in the tadpole tail identifies multiple resorption programs

Area of Science:

• Developmental Biology
• Molecular Endocrinology
• Cell Biology

Background:

• Amphibian metamorphosis involves significant tissue remodeling, including tail resorption.
• Thyroid hormone (TH) is a key regulator of this developmental process.
• Understanding the molecular mechanisms of TH action is crucial for deciphering developmental control.

Purpose of the Study:

• To investigate the spatial and temporal expression patterns of TH-responsive genes during amphibian tail resorption.
• To identify the specific cell types and molecular players involved in TH-induced tail resorption.
• To elucidate the genetic programs underlying the coordinated destruction of tail tissues.

Main Methods:

• In situ hybridization was used to localize gene expression within the resorbing tadpole tail.
• Expression patterns of thyroid hormone receptors (TRalpha, TRbeta) and their partners (RXRalpha, RXRbeta) were analyzed.
• Localization of early and delayed TH-responsive genes, including transcription factors and proteases, was determined.

Main Results:

• Thyroid hormone receptors and their partners are ubiquitously expressed in the tail.
• Early response genes are upregulated in cells undergoing differentiation and resorption.
• Delayed response genes, including proteolytic enzymes like stromelysin-3, are specifically expressed in invasive subepidermal fibroblasts.
• Fibroblasts surrounding muscle tissue show TH-induced gene activation, potentially leading to muscle cell death.

Conclusions:

• Invasive subepidermal fibroblasts are critical effectors of TH-induced tail resorption.
• Distinct genetic programs, regulated by TH, dictate the fate of various cell types within the tail.
• The coordinated action of TH-responsive genes in fibroblasts drives the overall resorption process.