Environmental influence on gametes and embryos

哺乳动物受精的一个普遍特征是，受精的精子会在卵子中引发一系列重复的钙振荡，这些振荡持续几个小时，最终形成原核。小鼠的这种钙振荡模式对于受精后卵子激活的早期事件和足月宫内发育都是必不可少的。精子内导致这些钙振荡的因素是一种睾丸特异性磷脂酶C，PLC Zeta，它在精子-卵子质膜融合后从精子头部释放出来，迄今在所有研究的哺乳动物精子中都发现了这种磷脂酶C，包括人类。钙的振荡也受鸡蛋内部因素的控制。正在使用小鼠模型进行研究，以检查卵子内负责控制钙振荡行为和钙再吸收的分子，这些过程对于受精时钙振荡的持续至关重要。我们发现，在成熟过程中，卵子通过低电压的T型钙通道吸收钙，这种钙吸收调节受精时观察到的钙振荡模式。使用缺乏STIM1和所有七个TRPC通道的小鼠的进一步研究表明，这些蛋白质都不是正常钙振荡所必需的。我们正在使用有条件的小鼠基因敲除策略从小鼠卵子中删除磷脂酶Cβ1，以确定鸡蛋蛋白是否需要产生正常的钙振荡。我们预计，通过更好地了解卵子激活过程中钙振荡行为的分子和细胞调控模式，我们可以了解环境因素和疾病状态是如何改变早期胚胎发育的。 许多必需的分子是由母体mRNAs编码的，这些mRNAs在卵母细胞成熟之前处于休眠状态。其中一个分子，MED13，是与RNA聚合酶相互作用调节转录的中介复合体的一个组成部分。我们目前正在研究MED13在早期植入前胚胎发育过程中编程基因表达的功能。这些研究将阐明暴露在环境化学品中可能扰乱并可能影响人类生育能力的基本遗传过程。

A universal feature of fertilization in mammals is that the fertilizing sperm evokes a series of repetitive calcium oscillations in the egg that persist for several hours and terminate with pronucleus formation. This pattern of calcium oscillations in mice is essential for both early events of egg activation in response to fertilization and for full term intrauterine development to occur. The factor within sperm responsible for inducing these calcium oscillations is a testis-specific phospholipase C, PLC zeta, which is released from the sperm head after sperm-egg plasma membrane fusion, and is found in all mammalian sperm studied to date, including human. Calcium oscillations are also controlled by factors within the egg. Studies are being performed using the mouse model to examine molecules within the egg that are responsible for controlling calcium oscillation behavior and calcium reuptake, processes that are essential for the continuation of calcium oscillations at fertilization. We found that during maturation, eggs take up calcium via low voltage, T-type calcium channels and that this calcium uptake regulates the calcium oscillatory pattern observed at fertilization. Additional studies using mice lacking STIM1 and all seven TRPC channels demonstrated that none of these proteins are required for normal calcium oscillations. We are in the process of deleting phospholipase C beta 1 from mouse eggs using a conditional mouse knockout strategy to determine if the egg protein is needed for production of normal calcium oscillations. We anticipate that by achieving a better understanding of the molecular and cellular modes of regulation of calcium oscillatory behavior during egg activation, we can learn how early embryo development is altered by environmental factors and by disease states. A number of essential molecules are encoded by maternal mRNAs that are dormant until oocyte maturation. One of these molecules, MED13, is a component of the Mediator complex that interacts with RNA polymerase to regulate transcription. We are currently examining the function of MED13 in programming gene expression during early preimplantation embryo development. These studies will shed light on basic genetic processes that can be disrupted by exposure to environmental chemicals and could impact on human fertility.