Thyroid Hormone Receptors in Two Model Species for Vertebrate Embryonic Development: Chicken and Zebrafish

Abstract

Chicken and zebrafish are two model species regularly used to study the role of thyroid hormones in vertebrate development. Similar to mammals, chickens have one thyroid hormone receptor α (TRα) and one TRβ gene, giving rise to three TR isoforms: TRα, TRβ2, and TRβ0, the latter with a very short amino-terminal domain. Zebrafish also have one TRβ gene, providing two TRβ1 variants. The zebrafish TRα gene has been duplicated, and at least three TRα isoforms are expressed: TRαA1-2 and TRαB are very similar, while TRαA1 has a longer carboxy-terminal ligand-binding domain. All these TR isoforms appear to be functional, ligand-binding receptors. As in other vertebrates, the different chicken and zebrafish TR isoforms have a divergent spatiotemporal expression pattern, suggesting that they also have distinct functions. Several isoforms are expressed from the very first stages of embryonic development and early chicken and zebrafish embryos respond to thyroid hormone treatment with changes in gene expression. Future studies in knockdown and mutant animals should allow us to link the different TR isoforms to specific processes in embryonic development.

Developmental toxicity of the PBDE metabolite 6-OH-BDE-47 in zebrafish and the potential role of thyroid receptor β

“…The thyroid nuclear receptor is encoded by two genes, TRα and TRβ. TR isoform expression varies dependent upon the tissue, developmental stage, and species (reviewed in Darras et al, 2011; Nelson and Habibi, 2009) TRα is expressed earlier and at higher levels than TRβ, but both are present at the midblastula stage and subsequent stages examined in this study (Essner et al, 1997; Liu et al, 2000; Power et al, 2001)…”

Maternal Thyroid and Glucocorticoid Hormone Interactions in Larval Fish Development, and Their Applications in Aquaculture

“…Although some authors conclude that the physiological significance of maternally derived cortisol in fish eggs is uncertain, it appears likely that permissive or synergistic actions of corticoids in thyroid-regulated processes may be of adaptive value (Brooks et al, 1997). Very early contributions of maternal THs to larval differentiation and survival are confirmed by the presence of thyroid hormone receptors (THR) long before endogenous thyroid hormone synthesis begins; several isoforms are expressed from the very first stages of development in zebrafish (Darras et al, 2011). Genes encoding the TRaA1 thyroid hormone receptor (TR) begin expression in zebrafish zygotes about 3 hr post-fertilization (Essner et al, 1997), suggesting that hormone responsiveness is an urgent embryonic need.…”

“…Genes encoding the TRaA1 thyroid hormone receptor (TR) begin expression in zebrafish zygotes about 3 hr post-fertilization (Essner et al, 1997), suggesting that hormone responsiveness is an urgent embryonic need. The detection of THR long before the onset of larval thyroid function in zebrafish has led to some doubt of the physiological role of hormone-receptor endocrine signaling in early development (Essner et al, 1997; discussed by Power et al, 2001), but zebrafish embryos have (Walpita et al, 2007) and are capable of responding to THs of maternal origin (Darras et al, 2011).…”

Maternal-Fetal Thyroid Interactions

“…about the developmental thyroid hormone mechanisms (deiodinases, transporters, sulfotransferases and receptors) in human [1,2,50,52,127,130,[151][152][153][154], rat [1,2,41,60,135,[154][155][156] and chicken [7,[157][158][159][160][161][162][163][164][165][166][167][168][169][170]. Note that the chicken is born early compared to the rat and human, as well as the rat is born early compared to the human (Table 6).…”