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。我们正在研究PLC zeta在临床体外受精程序完成后获得的人类精子样本中的功能。到目前为止，我们已经招募了大约160对不育夫妇参与研究，并从70多个程序中获得了精子样本，这是我们最终样本数量目标的一半。我们假设，缺乏足够的PLC zeta活性来诱导卵子激活所需的适当钙振荡，可以解释不孕夫妇的一系列失败，包括受精失败，胚胎植入前发育不良，甚至临床妊娠随后流产。

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. We are studying PLC zeta function in human sperm samples obtained at completion of clinical in vitro fertilization procedures. To date we have enrolled about 160 infertile couples in the study and obtained sperm samples from over 70 procedures, 1/2 of our final sample number goal. We hypothesize that a lack of sufficient PLC zeta activity to induce appropriate calcium oscillations required for egg activation could explain a spectrum of failure for the infertile couple, including failed fertilization, poor preimplantation embryo development, and even clinical pregnancy followed by miscarriage. Calcium oscillations are also controlled by factors within the egg. Additional 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 are in the process of generating a conditional mouse knockout of the phospholipase C beta 1 gene. This gene will be genetically deleted from mouse eggs to determine if the egg protein is needed for production of functional calcium oscillations. We have just completed and published a set of studies documenting that calcium entry from the environment surrounding the fertilized egg is critical for successful egg activation. 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 is a component of the Mediator complex that helps regulate transcription from the embryonic DNA. We are currently examining the function of a mediator complex subunit 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.