Oral-aboral axis specification in the sea urchin embryo -: II.: Mitochondrial distribution and redox state contribute to establishing polarity in Strongylocentrotus purpuratus
Oral-aboral axis specification in the sea urchin embryo -: II.: Mitochondrial distribution and redox state contribute to establishing polarity in Strongylocentrotus purpuratus
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DOI：
10.1016/j.ydbio.2004.06.005
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发表时间：
2004-09-01
影响因子：
2.7
通讯作者：
Robertson, AJ
中科院分区：
文献类型：
--
作者：
Coffman, JA;McCarthy, JJ;Robertson, AJ
最初的不对称性，指定的oral-aboral（OA）轴的海胆胚胎长期以来一直是一个谜。以前的研究表明，OA极性可以通过施加呼吸不对称性在胚胎中产生，胚胎的最氧化侧倾向于发育为口极。这表明，最早可观察到的不对称之一，沿着初期OA轴，氧化还原梯度建立了一个较高的密度和/或活性的线粒体的未来口侧的胚胎，可能发挥因果关系的作用，在建立轴。在这里，我们研究这个早期的氧化还原梯度的起源和功能意义。使用MitoTracker绿色，我们表明，线粒体是不对称分布在未受精卵的圆海胆，和极性的母亲不对称性保持在受精卵。活体染色表明，继承线粒体密度最高的胚胎一侧倾向于发育成口极。当线粒体通过离心卵或通过将纯化的线粒体转移到受精卵中而重新分布时，这种相关性成立，这表明不对称的线粒体分布可能通过对细胞内氧化还原状态的影响来夹带OA极性。在支持这种可能性，我们发现，规范的口腔外胚层被抑制时，胚胎培养在低氧条件下，强制执行一个相对还原的氧化还原状态。这种效果是逆转过表达的nodal，早期合子标记的口头规范，其本地化的表达足以组织整个OA轴，表明氧化还原状态的上游节点的表达。因此，我们提出，细胞内氧化的阈值水平是需要有效地激活节点，并过早达到这个阈值内含有最高密度的线粒体的卵裂球的结果在不对称的节点活动和随之而来的规格的OA轴。(C)2004年爱思唯尔公司All rights reserved.
The initial asymmetry that specifies the oral-aboral (OA) axis of the sea urchin embryo has long been a mystery. It was shown previously that OA polarity can be entrained in embryos by imposing a respiratory asymmetry, with the most oxidizing side of the embryo tending to develop as the oral pole. This suggests that one of the earliest observable asymmetries along the incipient OA axis, a redox gradient established by a higher density and/or activity of mitochondria on the prospective oral side of the embryo, might play a causal role in establishing the axis. Here, we examine the origin and functional significance of this early redox gradient. Using MitoTracker Green, we show that mitochondria are asymmetrically distributed in the unfertilized egg of Strongylocentrotus purpuratus, and that the polarity of the maternal asymmetry is maintained in the zygote. Vital staining indicates that the side of the embryo that inherits the highest density of mitochondria tends to develop into the oral pole. This correlation holds when mitochondria are redistributed by centrifugation of eggs or by transfer of purified mitochondria into zygotes, indicating that an asymmetric mitochondrial distribution can entrain OA polarity, possibly through effects on intracellular redox state. In support of this possibility, we find that specification of oral ectoderm is suppressed when embryos are cultured under hypoxic conditions that enforce a relatively reducing redox state. This effect is reversed by overexpression of nodal, an early zygotic marker of oral specification whose localized expression suffices to organize the entire OA axis, indicating that redox state is upstream of nodal expression. We therefore propose that a threshold level of intracellular oxidation is required to effectively activate nodal, and that precocious attainment of this threshold within the blastomeres containing the highest density of mitochondria results in asymmetric nodal activity and consequent specification of the OA axis. (C) 2004 Elsevier Inc. All rights reserved.