Physiological roles of glucocorticoids during early embryonic development of the zebrafish (Danio rerio)

Abstract

Key points• Glucocorticoids are known to be present in the developing zebrafish embryo but little is known about their physiological role at this early stage.• The zebrafish embryo demonstrates a functional glucocorticoid system from around 48 h post fertilisation.• This system and the stress response is amenable to pharmacological and genetic manipulation in a manner predicted by mammalian physiology.• Glucocorticoids play a key developmental role in hatching, swimming and stress response.• The zebrafish embryo is a relevant model for the study of glucocorticoid physiology.Abstract While glucocorticoids (GCs) are known to be present in the zebrafish embryo, little is known about their physiological roles at this stage. We hypothesised that GCs play key roles in stress response, hatching and swim activity during early development. To test this, whole embryo cortisol (WEC) and corticosteroid-related genes were measured in embryos from 6 to 120 h post fertilisation (hpf) by enzyme linked immunosorbent assay (ELISA) and quantitative real-time polymerase chain reaction (qRT-PCR). Stress response was assessed by change in WEC following stirring, hypoxia or brief electrical impulses applied to the bathing water. The impact of pharmacological and molecular GC manipulation on the stress response, spontaneous hatching and swim activity at different stages of development was also assessed. WEC levels demonstrated a biphasic pattern during development with a decrease from 0 to 36 hpf followed by a progressive increase towards 120 hpf. This was accompanied by a significant and sustained increase in the expression of genes encoding cyp11b1 (GC biosynthesis), hsd11b2 (GC metabolism) and gr (GC receptor) from 48 to 120 hpf. Metyrapone (Met), an inhibitor of 11β-hydroxylase (encoded by cyp11b1), and cyp11b1 morpholino (Mo) knockdown significantly reduced basal and stress-induced WEC levels at 72 and 120 hpf but not at 24 hpf. Spontaneous hatching and swim activity were significantly affected by manipulation of GC action from approximately 48 hpf onwards. We have identified a number of key roles of GCs in zebrafish embryos contributing to adaptive physiological responses under adverse conditions. The ability to alter GC action in the zebrafish embryo also highlights its potential value for GC research.

Programming of the hypothalamic-pituitary-interrenal axis by maternal social status in zebrafish (Danio rerio)

“…Cortisol concentrations and mRNA abundance of HPI axis genes have been well characterized throughout development in zebrafish (Alsop and Vijayan, 2008;Alderman and Bernier, 2009;Wilson test was used to evaluate the effect of maternal social status on the production of a viable clutch. Maternal cortisol levels as well as maternal treatment effects on embryo size, survival at 24 hpf, hatching, baseline or stress-induced cortisol levels, and mRNA abundance were analysed by one-way ANOVA.…”

“…Ontogeny of the hypothalamic-pituitary-interrenal (HPI) axis has been well studied in zebrafish (Alsop and Vijayan, 2008;Alderman and Bernier, 2009;Wilson et al, 2013), providing the necessary groundwork for investigating effects of maternal social stress. Specific maternal mRNAs associated with the HPI axis are transferred to eggs and play a key role in embryogenesis before embryos begin to synthesize mRNAs (i.e.…”

“…As embryos become transcriptionally active, mRNA abundance of HPI axis genes increases (Alsop and Vijayan, 2009). At this point, zebrafish larvae possess all of the machinery necessary to synthesize cortisol de novo, and by 72 h postfertilization (hpf), they begin to respond to stressors with an increase in cortisol levels (Alderman and Bernier, 2009;Wilson et al, 2013). …”

A time‐course transcriptional kinetics of the hypothalamic–pituitary–gonadal and hypothalamic–pituitary–adrenal axes in zebrafish eleutheroembryos after exposure to norgestrel

“…The transcript of the Star gene was significantly induced during embryogenesis, indicating onset of the steroid biosynthetic pathway. Because Cyp11b is the final enzyme in the pathway of cortisol biosynthesis, this could limit cortisol production during the early stages of development [24]. Moreover, Hsd11b2 has been suggested to be involved in metabolizing cortisol to cortisone to protect embryos from excess cortisol exposure by eliminating receptor binding [24,25].…”

“…Therefore, our results suggest that norgestrel has potential effects on the production of androgens by affecting Hsd17b3 and Hsd11b2 transcripts, which could interfere with embryonic brain development and sexual differentiation of gonads. Furthermore, biosynthesis of cortisol may also be changed because Hsd11b2 has been suggested to be associated with the metabolism of cortisol [24,25].…”