Environmental influence on gametes and embryos

哺乳动物受精的一个普遍特征是，受精的精子在卵子中引起一系列重复的钙振荡，这种振荡持续数小时，并以原核形成结束。小鼠体内钙振荡的这种模式对于受精后卵子激活的早期事件和足月子宫内发育的发生都是必不可少的。精子中负责诱导这些钙振荡的因素是睾丸特异性磷脂酶C， PLC zeta，它在精卵质膜融合后从精子头部释放出来，迄今为止研究的所有哺乳动物精子中都有发现，包括人类。钙离子的振荡也受到卵子内部因素的控制。研究人员正在使用小鼠模型来检查卵子内负责控制钙振荡行为和钙再摄取的分子，这些过程对受精时钙振荡的持续至关重要。我们发现，在小鼠卵母细胞成熟或受精过程中，钙进入体细胞的主要机制，即储存操作钙进入，并不是必需的。取而代之的是使用替代通道，包括电压操作钙通道CaV3.2和瞬态受体电位通道TRPM7。我们还发现，不同常见实验室小鼠品系的卵子在受精后第一次钙瞬态的持续时间和最大振幅、振荡频率和钙储存方面存在显著差异。这些钙振荡模式的差异是由于不同小鼠品系中卵细胞因子的变化。我们的研究结果支持鸡蛋内在特性在确定钙振荡模式中的重要性，并对受精时钙动力学的研究的解释和比较具有重要意义。在我们正在进行的研究中，我们正在确定受精后钙进入卵子的其他机制。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节模式，我们可以了解早期胚胎发育是如何被环境因素和疾病状态改变的。

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 the major mechanism of calcium entry in somatic cells, known as store-operated calcium entry, is not necessary for calcium entry during oocyte maturation or at fertilization in mice. Instead, alternate channels are utilized including the voltage operated calcium channel, CaV3.2, and the transient receptor potential channel, TRPM7. We also found that eggs from different common laboratory mouse strains have significant differences in the duration and maximum amplitude of the first calcium transient following fertilization, frequency of oscillations, and calcium stores. These differences in calcium oscillation patterns result from variation in egg factors across different mouse strains. Our results support the importance of egg-intrinsic properties in determining calcium oscillation patterns and have important implications for the interpretation and comparison of studies on calcium dynamics at fertilization. In our ongoing studies, we are determining additional mechanisms by which calcium enters the egg following fertilization. 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 but critically important for fertilization and the early steps of embryonic development. One of these steps, embryonic genome activation (EGA), is orchestrated by an intrinsic developmental program initiated during oocyte maturation. We published work showing that tankyrase, a poly(ADP-ribosyl) polymerase that regulates beta-catenin levels, undergoes programmed translation during oocyte maturation and serves an essential role in mouse EGA. Newly translated tankyrase triggers proteasomal degradation of axin, reducing targeted destruction of beta-catenin and promoting beta-catenin-mediated transcription of target genes, including Myc. MYC mediates ribosomal RNA transcription in 2-cell embryos, supporting global protein synthesis. Suppression of tankyrase activity using knockdown or chemical inhibition causes loss of nuclear beta-catenin and global reductions in transcription and histone H3 acetylation. Chromatin and transcriptional profiling indicate that development arrests prior to the mid-2-cell stage, mediated in part by reductions in beta-catenin and MYC. These findings indicate that post-transcriptional regulation of tankyrase serves as a ligand-independent developmental mechanism for post-translational -catenin activation and is required to complete EGA. These studies shed light on basic genetic processes that can be disrupted by exposure to environmental chemicals and could impact on human fertility.