Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5B3, Canada.
School of Environment and Sustainability, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5C8, Canada.
Aquat Toxicol. 2019 Nov;216:105299. doi: 10.1016/j.aquatox.2019.105299. Epub 2019 Sep 16.
Selenium (Se) is an essential trace element of concern that is known to contaminate aquatic ecosystems as a consequence of releases from anthropogenic activities. Selenium is of particular toxicological concern for egg-laying vertebrates as they bioaccumulate Se through the diet and deposit excess Se to embryo-offspring via maternal transfer, a process which has been shown to result in significant teratogenic effects. The purpose of the present study was to determine and compare the in ovo effects of Se exposure on early development of a laboratory model fish species native to North American freshwater systems, the fathead minnow (Pimephales promelas), through two different exposure routes, maternal transfer and microinjection. For maternal transfer studies, fathead minnow breeding groups (3 females: 2 males) were exposed to diets containing Se-background levels (1.21 μg Se/g food, dry mass [dm]) or environmentally relevant concentrations of selenomethionine (SeMet; 3.88, 8.75 and 26.5 μg Se/g food dm) and bred for 28 days. Embryos were collected at different time points throughout the study to measure Se concentrations and to assess teratogenicity in embryos. While exposure to dietary Se did not negatively affect fecundity among treatment groups, the lowest treatment group (3.88 μg Se/g food dm) produced on average the most embryos per day, per female. The maternal transfer of excess Se occurred rapidly upon onset of exposure, reaching steady-state after approximately 14 days, and embryo Se concentrations increased in a dose-dependent manner. The greatest concentrations of maternally transferred Se significantly increased the total proportion of deformed embryo-larval fathead minnows but did not impact hatchability or survival. In a second study, fathead minnow embryos were injected with SeMet at concentrations of 0.00 (vehicle control), 9.73, 13.5 and 18.9 μg Se/g embryo dm. Microinjection of SeMet did not affect hatchability but significantly increased the proportion of deformed embryo-larval fish in a dose-dependent manner. There was a greater proportion of deformed fathead minnows at embryo Se concentrations of 18.9 μg Se/g embryo dm when exposed via microinjection versus maternal transfer at concentrations of 28.4 μg Se/g embryo dm. However, the findings suggest that both exposure routes induced analogous developmental toxicities in early life stage fish at Se concentrations between 9.73 and 13.5 μg Se/g embryo dm. Overall, this study demonstrated that microinjection has utility for studying the effects of Se in embryo-larval fish and is a promising method for the study of early life stage Se exposure in egg-laying vertebrates.
硒 (Se) 是一种必需的微量元素，由于人为活动的释放，已知会污染水生生态系统。硒对产蛋脊椎动物具有特殊的毒理学关注，因为它们通过饮食生物积累硒，并通过母体转移将多余的硒沉积到胚胎后代中，这一过程已被证明会导致严重的致畸作用。本研究的目的是通过两种不同的暴露途径，即母体转移和微注射，确定并比较暴露于硒对原产于北美的淡水系统的实验室模式鱼类——黑头呆鱼（Pimephales promelas）早期发育的体内效应。对于母体转移研究，将黑头呆鱼繁殖组（3 只雌性：2 只雄性）暴露于含有硒背景水平（1.21μg Se/g 食物，干重 [dm]）或环境相关浓度的硒代蛋氨酸（SeMet；3.88、8.75 和 26.5μg Se/g 食物 dm）的饮食中，并繁殖 28 天。在整个研究过程中，不同时间点采集胚胎以测量硒浓度并评估胚胎的致畸性。虽然饮食中硒的暴露不会影响处理组的繁殖力，但最低处理组（3.88μg Se/g 食物 dm）平均每天每只雌性产仔数最多。母体过度转移硒的速度很快，在暴露开始时就会发生，大约 14 天后达到稳定状态，胚胎中的硒浓度呈剂量依赖性增加。母体转移的最大浓度显著增加了畸形黑头呆鱼胚胎-幼鱼的总比例，但不影响孵化率或存活率。在第二项研究中，将 SeMet 以 0.00（载体对照）、9.73、13.5 和 18.9μg Se/g 胚胎 dm 的浓度注射到黑头呆鱼胚胎中。SeMet 的微注射不影响孵化率，但以剂量依赖性方式显著增加了畸形胚胎-幼鱼的比例。当通过微注射在胚胎中暴露于 18.9μg Se/g 胚胎 dm 的 SeMet 浓度时，与在胚胎中暴露于 28.4μg Se/g 胚胎 dm 的浓度相比，畸形黑头呆鱼的比例更高。然而，研究结果表明，在 9.73 至 13.5μg Se/g 胚胎 dm 的 Se 浓度下，两种暴露途径都在早期生命阶段鱼类中诱导了类似的发育毒性。总体而言，这项研究表明，微注射在研究胚胎-幼鱼中的硒效应方面具有实用性，并且是研究产蛋脊椎动物中早期生活阶段硒暴露的一种很有前途的方法。
