Thyroid hormone receptor expression in the obligatory paedomorphic salamander Necturus maculosus

Area of Science:

• Developmental Biology
• Endocrinology
• Evolutionary Biology

Background:

• Amphibian metamorphosis is regulated by thyroid hormones (TH) acting through thyroid hormone receptors (TRs).
• Necturus maculosus is an amphibian that exhibits obligate paedomorphosis, suggesting a lack of response to TH.
• Understanding TR gene expression is crucial for investigating TH-induced metamorphosis.

Purpose of the Study:

• To investigate thyroid hormone receptor (TR) gene expression patterns in Necturus maculosus.
• To examine the expression of TH-responsive genes (CTHBP and stromelysin 3) in Necturus maculosus.
• To determine if Necturus maculosus tissues are responsive to thyroid hormones.

Main Methods:

• In situ hybridization was employed to detect Necturus TRalpha and TRbeta gene expression.
• RNA probes were generated from cloned Necturus TRalpha and TRbeta genes.
• Tissue samples from Necturus maculosus were analyzed for gene expression.

Main Results:

• Necturus TRalpha gene expression was detected in the central nervous system, digestive and urinary epithelia, myocardium, and skeletal muscle.
• Necturus TRbeta gene expression was observed in the brain.
• Expression patterns of CTHBP and stromelysin 3 (ST3) were largely distinct from TR expression.

Conclusions:

• The presence of evolutionary conserved TRalpha and TRbeta genes suggests Necturus tissues express functional TRs.
• Contrary to previous hypotheses, Necturus maculosus tissues demonstrate TH responsiveness.
• This study challenges the notion of Necturus maculosus as completely unresponsive to thyroid hormones.