Maternal thyroid hormones affect zebrafish embryo development

Area of Science:

• Endocrinology
• Developmental Biology
• Aquatic Toxicology

Background:

• Thyroid hormones (THs) are crucial for vertebrate development, but maternal transfer and effects in fish are not well understood.
• The somatotropic axis, regulating growth and metabolism, is a key target of THs.

Purpose of the Study:

• To investigate the impact of maternal dietary thyroxine (T4) on zebrafish (Danio rerio) development.
• To understand the role of maternal THs in regulating embryonic T3 levels and the somatotropic axis.

Main Methods:

• Female zebrafish were fed diets supplemented with T4 (12.5 or 25 μg/g body weight/day) or a control diet.
• Maternal plasma TH levels were measured, and females were bred with untreated males.
• Embryos and larvae were analyzed for survival, heartbeat, morphology, T3 content, and gene expression from 0 to 144 hours post-fertilization.

Main Results:

• Maternal T4 supplementation increased embryonic T3 levels.
• Offspring exhibited growth retardation, edema, spinal deformities, tachycardia, and increased mortality.
• Gene expression analysis revealed dysregulation of TH axis components and somatotropic genes.

Conclusions:

• Maternal THs play a critical role in regulating embryonic development and growth trajectories in zebrafish.
• Excessive maternal T4 can disrupt normal development, leading to adverse outcomes in offspring.
• This study highlights the sensitivity of early fish development to maternal hormonal environments.