Biosciences, College of Life and Environmental Sciences, Geoffrey Pope Building, University of Exeter, Exeter, EX4 4QD, UK.
Centre for Environment, Fisheries and Aquaculture Science, Barrack Road, The Nothe, Weymouth, DT4 8UB, Dorset, UK.
Histochem Cell Biol. 2020 Nov;154(5):579-595. doi: 10.1007/s00418-020-01933-2. Epub 2020 Oct 21.
Silver is a non-essential, toxic metal widespread in freshwaters and capable of causing adverse effects to wildlife. Its toxic effects have been studied in detail but less is known about how sensitivity varies during development and whether pre-exposures affect tolerance upon re-exposure. We address these knowledge gaps using the zebrafish embryo (Danio rerio) model to investigate whether exposures encompassing stages of development prior to mid-blastula transition, when chorion hardening and epigenetic reprogramming occur, result in greater toxicity compared to those initiated after this period. We conducted exposures to silver initiated at 0.5 h post fertilisation (hpf) and 4 hpf to determine if toxicity differed. In parallel, we exposed embryos to the methylation inhibitor 5-azacytidine as a positive control. Toxicity increased when exposures started from 0.5 hpf compared to 4 hpf and LC50 were significantly lower by 1.2 and 7.6 times for silver and 5-azacyitidine, respectively. We then investigated whether pre-exposure to silver during early development (from 0.5 or 4 hpf) affected the outcome of subsequent exposures during the larvae stage, and found no alterations in toxicity compared to naïve larvae. Together, these data demonstrate that during early development zebrafish embryos are more sensitive to silver when experiments are initiated at the one-cell stage, but that pre-exposures do not influence the outcome of subsequent exposures, suggesting that no long-lasting memory capable of influencing future susceptibility was maintained under our experimental conditions. The finding that toxicity is greater for exposures initiated at the one-cell stage has implications for designing testing systems to assess chemical toxicity.
银是一种非必需的有毒金属，广泛存在于淡水中，能够对野生动物产生不利影响。其毒性作用已被详细研究，但对于其在发育过程中的敏感性变化以及预先暴露是否会影响再次暴露时的耐受性知之甚少。我们使用斑马鱼胚胎（Danio rerio）模型来解决这些知识空白，以研究在中囊胚转换之前开始的暴露（当卵壳变硬和表观遗传重编程发生时）是否会比在此之后开始的暴露产生更大的毒性。我们进行了从受精后 0.5 小时（hpf）和 4 hpf 开始的银暴露实验，以确定毒性是否不同。平行地，我们用 5-氮杂胞苷作为阳性对照来暴露胚胎。与从 4 hpf 开始的暴露相比，从 0.5 hpf 开始的暴露毒性增加，LC50 值分别降低了 1.2 和 7.6 倍，分别为银和 5-氮杂胞苷。然后，我们研究了早期发育过程中（从 0.5 或 4 hpf）预先暴露于银是否会影响幼虫期随后暴露的结果，与未接触的幼虫相比，毒性没有变化。总的来说，这些数据表明，在早期发育阶段，当实验从单细胞阶段开始时，斑马鱼胚胎对银更敏感，但预先暴露不会影响随后暴露的结果，这表明在我们的实验条件下，没有能够影响未来易感性的持久记忆被维持。在单细胞阶段开始的暴露毒性更大的发现，对于设计评估化学毒性的测试系统具有重要意义。
