Gallicano G I, Schwarz S M, McGaughey R W, Capco D G
Department of Zoology, Arizona State University, Tempe 85287-1501.
Dev Biol. 1993 Mar;156(1):94-106. doi: 10.1006/dbio.1993.1061.
We investigated the signal transduction pathways that mediate activation of Syrian hamster eggs. Under conditions in which the concentration of intracellular free calcium ([Ca2+]i) is clamped low, activation of protein kinase C (PKC) can induce second polar body formation, reformation of the nuclear envelope, and decondensation of chromatin, as well as golgi reformation. However, calcium is necessary for normal transition from meiotic metaphase II to anaphase II. Conversely, under conditions in which the level of PKC activity is clamped low, induction of a rise in [Ca2+]i, using the calcium ionophore A23187, does not induce egg activation. These results strongly suggest that PKC acts after the calcium signal as a proximal inducer of egg activation. This suggestion is supported by the kinetics of egg activation; PKC stimulators activate the eggs at a significantly enhanced rate (P < 0.01) compared with activation by calcium ionophore. We show here that PKC stimulators induce emission of the second polar body, but that subsequently, with longer culture, the emitted polar body is absorbed. Our results suggest that the rise in [Ca2+]i serves two functions, to activate PKC and to induce the transition from metaphase II to anaphase II. PKC, once activated, mediates several other events of egg activation.
我们研究了介导叙利亚仓鼠卵激活的信号转导途径。在细胞内游离钙浓度（[Ca2+]i）被钳制在低水平的条件下，蛋白激酶C（PKC）的激活可诱导第二极体形成、核膜重塑、染色质解聚以及高尔基体重塑。然而，钙对于从减数分裂中期II正常过渡到后期II是必需的。相反，在PKC活性水平被钳制在低水平的条件下，使用钙离子载体A23187诱导[Ca2+]i升高并不会诱导卵激活。这些结果强烈表明，PKC在钙信号之后作为卵激活的近端诱导剂起作用。这一观点得到了卵激活动力学的支持；与钙离子载体激活相比，PKC刺激剂以显著更高的速率（P < 0.01）激活卵。我们在此表明，PKC刺激剂诱导第二极体排出，但随后，随着培养时间延长，排出的极体会被吸收。我们的结果表明，[Ca2+]i升高具有两种功能，即激活PKC以及诱导从中期II到后期II的转变。PKC一旦被激活，就介导卵激活的其他几个事件。
