Involvement of thyroid hormones in chicken embryonic brain development

Area of Science:

• Developmental biology
• Neuroscience
• Endocrinology

Background:

• Thyroid hormones (THs) are vital for brain development, coordinating cell proliferation, migration, and differentiation.
• Existing research primarily focuses on late brain development, with limited understanding of early stages before embryonic TH secretion.

Purpose of the Study:

• To investigate the role of THs in both early and late brain development using the chick embryo model.
• To analyze the expression patterns of proteins regulating TH bioavailability and action during development.

Main Methods:

• Detection of T(4) and T(3) in chicken brain from early developmental stages (day 4).
• Analysis of ontogenetic expression profiles for TH transporters, deiodinases, and TH-receptors.
• Induction of hypothyroidism to assess effects on brain development.
• Microarray analysis of telencephalon gene expression in hypothyroid embryos.
• In vivo knockdown studies using chick embryos cultured ex ovo.

Main Results:

• THs (T(4) and T(3)) are present in chicken brains from day 4.
• Proteins regulating THs are expressed early (day 2) and throughout brain development (from day 4), with dynamic spatial and temporal distribution.
• Hypothyroidism during late incubation disrupts cerebellar cell migration.
• Gene expression in the telencephalon diverges in hypothyroid embryos during early development.

Conclusions:

• THs are essential for both early and late stages of chick brain development.
• The chick embryo provides a valuable model for studying THs' role in early brain development, particularly with ex ovo culture techniques.