Troponin T isoform expression is modulated during Atlantic halibut metamorphosis

Area of Science:

• Developmental Biology
• Molecular Biology
• Fish Biology

Background:

• Flatfish metamorphosis is a complex, thyroid hormone (TH)-driven transformation from larva to juvenile.
• The impact of THs on skeletal muscle sarcomeric protein genes during this process is not well understood.
• Troponin T (TnT) is crucial for muscle contraction and sarcomere assembly, making its study during metamorphosis important.

Purpose of the Study:

• To investigate the changes in Troponin T (TnT) gene expression during flatfish metamorphosis.
• To determine the role of thyroid hormones (THs) in regulating TnT gene expression in flatfish muscle.
• To analyze the symmetry and muscle fiber organization in relation to TnT gene expression.

Main Methods:

• Cloning of five complementary DNAs (cDNAs) for halibut TnT genes, including splice variants and novel isoforms.
• Analysis of TnT gene expression patterns during natural and T4-induced metamorphosis.
• Assessment of muscle symmetry and temporal-spatial expression of TnT genes.

Main Results:

• Five halibut TnT cDNAs were identified, including fast TnT (fTnT) variants, a novel slow muscle-specific fTnT-like (AfTnT), and sTnT2.
• THs modulated fTnT isoform expression from basic to acidic during metamorphosis.
• Expression of red muscle-specific genes (AfTnT, sTnT2) remained unchanged, and muscle organization stayed symmetrical.

Conclusions:

• Halibut muscle organization remains symmetrical post-metamorphosis, indicating molecular adaptations driven by THs.
• Species-specific differences in TnT gene expression may underlie varied larval muscle development programs in teleosts.
• These adaptations likely enhance survival by fitting teleosts to specific ecological niches.