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。蝾螈（Cynopspyrrhogaster）的未受精卵在第二个减数分裂中期被捕获。 [Ca^2>]_i 的短暂增加是引起卵子激活的主要信号，其由精子受精触发并作为Ca^2 波在卵子皮层上传播。将蝾螈精子提取物（SE）注射到未受精卵中，引起波状[Ca^2>]_i增加，然后卵子经历激活并恢复减数分裂。在注射 SE 的鸡蛋中，不仅证实了细胞周期蛋白 B1 的降解，而且还证实了 DNA 的复制。当 SE 在注射前煮沸或用蛋白酶 K 处理时，导致卵子活化的活性就会丧失。在SE注射之前预注射Ca 2+ -螯合剂BAPTA抑制卵激活。这些结果表明，精子细胞质中的不耐热蛋白因子诱导了卵子活化所必需的[Ca^2]_i的短暂增加。向未受精卵中注射IP_3引起[Ca^2>]_i增加和卵激活，但注射cADP-核糖则没有。此外，预注射肝素（IP_3 受体抑制剂）可通过使精子受精或 SE 注射来防止卵子活化。这些结果表明，不仅受精，而且SE注射也通过IP_3受体而不是钛利尼定受体诱导[Ca^2]_i增加。

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.