A study of an egg-activating molecule in the sperm cytoplasm

在我们的研究中，我们发现了以下主要结果。在第二次减数分裂中期，食蟹猴的未受精卵停止生长。由精子受精触发的短暂的[Ca^&lt；2&gt；]_i升高是引起卵子激活的主要信号，它以Ca^&lt；2&gt；波的形式通过卵子皮质传播。向未受精卵注射食蟹精子提取液(SE)后，[Ca^&lt；2&gt；]_i呈波浪状升高，卵子开始激活并恢复减数分裂。在注射SE的卵子中，不仅证实了Cyclin B1的降解，而且证实了DNA的复制。当SE在注射前被煮沸或用蛋白酶K处理时，引起卵子激活的活性丧失。SE注射前预先注射钙离子螯合剂BAPTA可抑制卵子激活。这些结果表明，精子胞质中的一种不稳定的蛋白因子导致卵子激活所必需的[Ca^；2]_i一过性升高。未受精卵注射IP_3可引起[Ca~(2+)]_i升高和卵子激活，而注射cADP-核糖则无此作用。此外，预先注射IP_3受体的抑制剂肝素可通过使精子受精或注射SE来阻止卵子激活。这些结果表明，不仅受精，而且注射SE也通过IP_3受体而不是钛核苷受体诱导[Ca~(2+)]_i升高。

In our study, we have found the following major results. Unfertilized eggs of the newt, Cynops pyrrhogaster, are arrested at the second meiotic metaphase. A transient increase of [Ca^<2+>]_i, which is triggered by fertilizing sperm and propagates over the egg cortex as Ca^<2+> wave, is a primary signal to cause egg activation. The injection of an extract of Cynops sperm (SE) into the unfertilized eggs induced the wave-like [Ca^<2+>]_i increase, and then the eggs underwent activation and resumption of meiosis. In the SE-injected eggs, not only degradation of cyclin B1, but also DNA replication was confirmed. When SE had been boiled or treated with Proteinase K before injection, the activity to cause egg activation was lost. Preinjection of Ca^<2+>-chelator BAPTA before SE-injection inhibited egg activation. These results indicate that a heat-labile and proteinous factor in sperm cytoplasm induces a transient increase of [Ca^<2+>]_i indispensable for egg activation. Injection of IP_3 into unfertilized eggs caused [Ca^<2+>]_i increase and egg activation, but injection of cADP-ribose did not. In addition, preinjection of heparin, an inhibitor of IP_3 receptors, prevented egg activation by fertilizing sperm or by SE-injection. These results indicate that not only fertilization, but also SE-injection induces [Ca^<2+>]_i increase through the IP_3 receptors, rather titan rianodine receptors.