Knockdown of Type 3 Iodothyronine Deiodinase Severely Perturbs Both Embryonic and Early Larval Development in Zebrafish

Abstract

Exposure to appropriate levels of thyroid hormones (THs) at the right time is of key importance for normal development in all vertebrates. Type 3 iodothyronine deiodinase (D3) is the prime TH-inactivating enzyme, and its expression is highest in the early stages of vertebrate development, implying that it may be necessary to shield developing tissues from overexposure to THs. We used antisense morpholino knockdown to examine the role of D3 during early development in zebrafish. Zebrafish possess 2 D3 genes, dio3a and dio3b. Here, we show that both genes are expressed during development and both contribute to in vivo D3 activity. However, dio3b mRNA levels in embryos are higher, and the effects of dio3b knockdown on D3 activity and on the resulting phenotype are more severe. D3 knockdown induced an overall delay in development, as determined by measurements of otic vesicle length, eye and ear size, and body length. The time of hatching was also severely delayed in D3-knockdown embryos. Importantly, we also observed a severe disturbance of several aspects of development. Swim bladder development and inflation was aberrant as was the development of liver and intestine. Furthermore, D3-knockdown larvae spent significantly less time moving, and both embryos and larvae exhibited perturbed escape responses, suggesting that D3 knockdown affects muscle development and/or functioning. These data indicate that D3 is essential for normal zebrafish embryonic and early larval development and show the value of morpholino knockdown in this model to further elucidate the specific role of D3 in some aspects of vertebrate development.

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

“…In this study, we used specific developmental staging metrics (HTA, OVL, eye pigmentation) to describe the developmental delays observed from exposure to 6-OH-BDE-47 or TDCs (Heijlen et al, 2014; Kimmel et al, 1995; Walpita et al, 2010, 2009). Additionally, positive control chemicals with known modes of action (IOP, PTU) were utilized to further examine their impacts on developmental morphology via thyroid hormone disruption Propylthiouracil targets thyroid peroxidase, and may inhibit DI 2 in fish species (Orozco et al 2000; Sanders et al, 1997; Visser et al1983).…”

“…These morphometric analyses were regarded as sensitive endpoints for thyroid disruption in zebrafish studies employing morpholino knockdown of deiodinase enzymes (Heijlen et al, 2014; Walpita et al, 2010). The HTA, OVL, and pigmentation enabled evaluation of developmental delays induced by 6-OH-BDE-47, thyroid disrupting chemicals, and native hormones.…”

“…Image J (NIH, Bethesda, MD) was used to quantify the HTA, OVL, and eye pigmentation in each embryo image (illustrated in Figure 1A) (Heijlen et al, 2014; Kimmel et al, 1995; Walpita et al, 2010, 2009) Briefly, the HTA is formed by a line between the head and body axis (parallel to the notochord in the midtrunk region at somite 5). This angle increases between 20 hpf and 70 hpf as a result of body straightening.…”

New insights into thyroid hormone action

“…D2 and D3 play a role in the developing cochlea: D3 acts prior to the onset of hearing by preventing the premature response to TH and after birth D2 amplifies T3 levels to triggers the onset of auditory function (Ng et al, 2004; Ng et al, 2009). Silencing D3 during development has detrimental effects as observed in zebrafish, which results in delayed hatching, significantly smaller size, and decreased inflation of the swim bladder (Heijlen et al, 2014). Striking studies in different species show that reactivation of D3 expression occurs in early phases of tissue regeneration e.g.…”

Thyroid disruption in zebrafish (Danio rerio) larvae: Different molecular response patterns lead to impaired eye development and visual functions

“…The eye and craniofacial development of vertebrates is a complex process that is partially regulated by thyroid hormones (Bohnsack and Kahana, 2013;Darras et al, 2015). Knock-down of specific thyroid-regulating genes as well as treatment with different thyroid disruptors resulted in reduced eye size, malformations of eyes and head, and disruption of retinal pigment cell layers of zebrafish larvae (Heijlen et al, 2014;Reider and Connaughton, 2014). It has been reported that cone photoreceptor development seems to be under direct regulation of thyroid hormones (Raine and Hawryshyn, 2009;Suzuki et al, 2013), and it has been described, that thyroid receptors are expressed in the outer nuclear layer of the retina, which contains the developing photoreceptors (Bertrand et al, 2007).…”