Deiodinase Knockdown during Early Zebrafish Development Affects Growth, Development, Energy Metabolism, Motility and Phototransduction

Abstract

Thyroid hormone (TH) balance is essential for vertebrate development. Deiodinase type 1 (D1) and type 2 (D2) increase and deiodinase type 3 (D3) decreases local intracellular levels of T3, the most important active TH. The role of deiodinase-mediated TH effects in early vertebrate development is only partially understood. Therefore, we investigated the role of deiodinases during early development of zebrafish until 96 hours post fertilization at the level of the transcriptome (microarray), biochemistry, morphology and physiology using morpholino (MO) knockdown. Knockdown of D1+D2 (D1D2MO) and knockdown of D3 (D3MO) both resulted in transcriptional regulation of energy metabolism and (muscle) development in abdomen and tail, together with reduced growth, impaired swim bladder inflation, reduced protein content and reduced motility. The reduced growth and impaired swim bladder inflation in D1D2MO could be due to lower levels of T3 which is known to drive growth and development. The pronounced upregulation of a large number of transcripts coding for key proteins in ATP-producing pathways in D1D2MO could reflect a compensatory response to a decreased metabolic rate, also typically linked to hypothyroidism. Compared to D1D2MO, the effects were more pronounced or more frequent in D3MO, in which hyperthyroidism is expected. More specifically, increased heart rate, delayed hatching and increased carbohydrate content were observed only in D3MO. An increase of the metabolic rate, a decrease of the metabolic efficiency and a stimulation of gluconeogenesis using amino acids as substrates may have been involved in the observed reduced protein content, growth and motility in D3MO larvae. Furthermore, expression of transcripts involved in purine metabolism coupled to vision was decreased in both knockdown conditions, suggesting that both may impair vision. This study provides new insights, not only into the role of deiodinases, but also into the importance of a correct TH balance during vertebrate embryonic development.

Thyroid hormone signaling specifies cone subtypes in human retinal organoids

“…Conversion of T4 to T3 occurs locally in target tissues to induce gene expression responses (34,35). Deiodinases, enzymes that modulate the levels of T3 and T4, are expressed in the retinas of mice, fish, and chicken (29,(36)(37)(38)(39)(40).…”

Mechanisms of Photoreceptor Patterning in Vertebrates and Invertebrates

“…They are expressed in regionalized areas and/or at different time points in the chick(169), mouse(210, 211), and zebrafish retinas(212-214). In mice, Deiodinase 2 (Dio2), which converts thyroid hormone from the inactive T4 to the active T3 form, is expressed at higher levels in the dorsal retina(210, 215) and likely establishes a T3 gradient(216) (Fig.…”

Impaired swim bladder inflation in early life stage fathead minnows exposed to a deiodinase inhibitor, iopanoic acid

“…Nonetheless, there is supporting evidence from a number of deiodinase knockdown studies that suggest a specific role for deiodinase activity in the process of swim bladder inflation (as well as numerous other developmental events in fish). For example, knockdown of dio1 and dio2 significantly reduced swim bladder inflation (96 hpf) in zebrafish [47], and knockout of dio2 in zebrafish also resulted in defects in swim bladder inflation [48]. Deiodinase 3 knockdown had an even more pronounced effect on swim bladder inflation, but also impacted both larval length and hatching success, suggesting perhaps a more systemic developmental impact [46,47].…”