School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA.
Integr Comp Biol. 2008 Sep;48(3):411-8. doi: 10.1093/icb/icn079. Epub 2008 Jul 31.
The discovery by Schwabl that maternal steroid hormones are transferred to the egg yolk and have effects on the phenotype of offspring revealed a new pathway for non-genetic maternal effects. The initial model relied on passive transfer. The thinking was that steroids passively entered the lipophillic yolk during yolk deposition and then were deposited in the yolk until they were passively delivered to the embryo as the yolk was used. Subsequent studies revealed that the system is much more dynamic than that. Here, we explore questions about how dynamic the system really is and look at questions like: Is transfer of maternal steroids to the yolk passive or is it actively regulated? At what stages of the maternal reproductive cycle are steroids transferred? During reproduction, how dynamic are the levels of yolk steroids? Especially in the case of potentially deleterious steroids (e.g., androgens in female offspring; glucocorticoids), once deposited can they come out of the yolk over time? Can they be metabolized by the yolk or by the embryo? During incubation, how much do steroid levels in the yolk change? Can steroids diffuse from the yolk to the embryo prior to yolk utilization? Does the embryo contribute to yolk steroid levels as it develops? We believe that comprehensive answers to questions like these will eventually allow us to generate a much more accurate and complete model of the transfer and utilization of yolk steroids and that this model will be much more dynamic and active than the one initially proposed.
施瓦布发现，母体类固醇激素被转移到蛋黄中，并对后代的表型产生影响，这揭示了非遗传母体效应的新途径。最初的模型依赖于被动转移。人们认为，类固醇在蛋黄沉积过程中被动进入亲脂性蛋黄，然后沉积在蛋黄中，直到蛋黄被被动输送到胚胎中，蛋黄被消耗。随后的研究表明，该系统比最初设想的要活跃得多。在这里，我们探讨了这个系统到底有多活跃的问题，并研究了一些问题，如：母体类固醇向蛋黄的转移是被动的还是主动调节的？在母体生殖周期的哪个阶段转移类固醇？在生殖过程中，蛋黄类固醇的水平有多活跃？特别是对于潜在有害的类固醇（例如，雌性后代中的雄激素；糖皮质激素），一旦沉积，它们是否会随着时间的推移从蛋黄中排出？它们是否可以被蛋黄或胚胎代谢？在孵化过程中，蛋黄中的类固醇水平会发生多大变化？在蛋黄被利用之前，类固醇是否可以从蛋黄扩散到胚胎中？胚胎在发育过程中是否会影响蛋黄类固醇水平？我们相信，对这些问题的全面回答最终将使我们能够生成一个更准确、更完整的蛋黄类固醇转移和利用模型，并且该模型将比最初提出的模型更加活跃和主动。
