Xu Z, Lefevre L, Ducibella T, Schultz R M, Kopf G S
Center for Research on Reproduction and Women's Health, University of Pennsylvania, Philadelphia, Pennsylvania, 19104-6080, USA.
Dev Biol. 1996 Dec 15;180(2):594-604. doi: 10.1006/dbio.1996.0331.
Results of numerous experiments indicate that the transient rise in intracellular Ca2+ following sperm-egg fusion is essential for the subsequent events that constitute egg activation. Some events of egg activation, e.g., cortical granule exocytosis, however, appear more sensitive to intracellular Ca2+ than other events, e.g., cell cycle resumption. To examine if specific events of egg activation have different thresholds for Ca2+, we manipulated buffered intracellular Ca2+ concentrations by microinjecting Ca2+-BAPTA buffers and then examined the effect on the cortical granule exocytosis, recruitment of maternal mRNAs, and cell cycle resumption. We find that whereas cortical granule exocytosis occurs over a narrow threshold range of injected free Ca2+ concentrations between 0.5 and 1.0 microM, recruitment of maternal mRNAs is only partially stimulated at injected free Ca2+ concentrations of 2.5 microM, and no evidence for cell cycle resumption was observed (up to 2.5 microM Ca2+). Although the Ca2+- and phospholipid-dependent protein kinase, protein kinase C, is implicated in aspects of egg activation, calmodulin is also a potential target for the transient increase in Ca2+ that occurs following fertilization. Whereas incubation of eggs in the presence of the calmodulin antagonist W-7 followed by insemination does not block cortical granule exocytosis, cell cycle resumption, as assessed by the metaphase-to-anaphase transition, a decrease in histone H1 kinase activity and the time course for the emission of the second polar body are significantly delayed/inhibited.
大量实验结果表明，精卵融合后细胞内Ca2+的短暂升高对于构成卵激活的后续事件至关重要。然而，卵激活的某些事件，如皮质颗粒胞吐作用，似乎比其他事件，如细胞周期恢复，对细胞内Ca2+更敏感。为了研究卵激活的特定事件是否对Ca2+有不同的阈值，我们通过显微注射Ca2+-BAPTA缓冲液来操纵缓冲的细胞内Ca2+浓度，然后检查其对皮质颗粒胞吐作用、母体mRNA募集和细胞周期恢复的影响。我们发现，虽然皮质颗粒胞吐作用在注射的游离Ca2+浓度介于0.5至1.0微摩尔之间的狭窄阈值范围内发生，但在注射游离Ca2+浓度为2.5微摩尔时，母体mRNA的募集仅受到部分刺激，并且未观察到细胞周期恢复的证据（高达2.5微摩尔Ca2+）。虽然Ca2+和磷脂依赖性蛋白激酶，即蛋白激酶C，与卵激活的某些方面有关，但钙调蛋白也是受精后发生的Ca2+短暂增加的潜在靶点。在存在钙调蛋白拮抗剂W-7的情况下孵育卵子然后进行授精，虽然不会阻断皮质颗粒胞吐作用，但通过中期到后期的转变、组蛋白H1激酶活性的降低以及第二极体释放的时间进程来评估，细胞周期恢复会显著延迟/受到抑制。
