Speksnijder J E
Department of Experimental Zoology, University of Utrecht, The Netherlands.
Dev Biol. 1992 Oct;153(2):259-71. doi: 10.1016/0012-1606(92)90111-s.
Ascidian eggs respond to fertilization with a series of repetitive calcium waves that originate mostly from the vegetal/contraction pole region (J. E. Speksnijder, C. Sardet, and L. F. Jaffe, 1990, Dev. Biol. 142, 246-249), where the myoplasm is concentrated during the first phase of ooplasmic segregation. This suggests that the myoplasm may be involved in initiating these calcium waves. To test this possibility, the starting position of the calcium waves was determined in eggs that had the subcortical, mitochondria-rich part of the myoplasm displaced by centrifugation. Such centrifuged eggs display four cytoplasmic layers: a large centrifugal yolk zone, a narrow clear zone, a mitochondria-rich layer, and a small clear zone at the centripetal pole. Imaging of the cytosolic calcium in centrifuged eggs that were injected with the calcium-specific photoprotein aequorin reveals a series of repetitive calcium waves after fertilization. About 70% of these waves start in the vegetal/contraction pole area, which is similar to the number of waves previously found to start in this area in uncentrifuged eggs. In contrast, only about 25% of the waves start close to the displaced mitochondria-rich layer. From this result it is concluded that the main wave initiation site is not displaced by the centrifugal forces that displace the subcortical, mitochondria-rich part of the myoplasm. Moreover, the observation that the animal-vegetal polarity of cortical components such as actin filaments and the endoplasmic reticulum has been retained after centrifugation further suggests that a cortical component located in the vegetal hemisphere--most likely the endoplasmic reticulum network in the cortical region of the myoplasm--is involved in initiating the repetitive calcium waves in the fertilized ascidian egg.
海鞘卵受精后会产生一系列重复性的钙波，这些钙波主要起源于植物极/收缩极区域（J. E. 斯佩克斯尼德、C. 萨德特和L. F. 贾菲，1990年，《发育生物学》第142卷，第246 - 249页），在卵质分离的第一阶段，肌质集中于此区域。这表明肌质可能参与引发这些钙波。为了验证这种可能性，在通过离心使肌质富含线粒体的皮质下部分发生移位的卵中，确定了钙波的起始位置。这种离心后的卵呈现出四层细胞质：一个大的离心卵黄区、一个狭窄的透明区、一个富含线粒体的层以及位于向心极的一个小透明区。对注射了钙特异性光蛋白水母发光蛋白的离心卵的胞质钙进行成像，结果显示受精后会出现一系列重复性的钙波。这些钙波中约70%始于植物极/收缩极区域，这与之前在未离心的卵中发现始于该区域的钙波数量相似。相比之下，只有约25%的钙波始于靠近移位的富含线粒体层的位置。从这个结果可以得出结论，主要的波起始位点并未因使肌质富含线粒体的皮质下部分发生移位的离心力而移位。此外，离心后肌动蛋白丝和内质网等皮质成分的动植物极性得以保留这一观察结果进一步表明，位于植物半球的一种皮质成分——很可能是肌质皮质区域的内质网网络——参与引发受精海鞘卵中的重复性钙波。
