CALCIUM INVOLVEMENT IN DEVELOPMENT OF CELLULAR POLARITY

钙参与细胞极性的发展

• 批准号: 6319689
• 负责人: S ROUX
• 金额: $ 0.21万
• 依托单位国家: 美国
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-12-01 至 2000-02-29
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6319689
• 关键词: CALCIUM; INVOLVEMENT; DEVELOPMENT; CELLULAR; POLARITY

The force of gravity can induce a variety of developmental events and growth responses in many different kinds of cells. How a single cell senses gravity and transduces this stimulus into a signal for a polarized response remains a mystery. Here we report first-time evidence that gravity can polarize the flow of the intracellular signaling ion, calcium, into and out of a single cell. Ceratopteris is an aquatic fern that generates large, single celled spores. After the germination of these spores has been initiated by light, there is a limited period of time, usually 24 hours, during which gravity can fix their developmental polarity. The results of polarity fixation are that the cell nucleus migrates downward, the plane of the first cell division is positioned asymmetrically and perpendicular to the vector of gravity, and the two cell types produced grow in opposite directions parallel to the vector of gravity. To investigate whether calcium is involved in this polarization event, we used a self-referencing calcium selective electrode (Kuhtreiber and Jaffe, 1990) and recorded the net movement of calcium acrosss the cell membrane at the top, side, and bottom of the spore after germination was initiated. A strong efflux of calcium was seen at the top of the spore, which increased sharply at approximately 6 hours after germination was initiated. There was also a calcium efflux from the sides of the spore, but it was 20 folds smaller than the top efflux. An influx of calcium was seen at the bottom of the spore peaking at 2 hours after the peak at the top. The movement of calcium was seen only in the first 24 hours after germination initiation, after which it declined at all three points to low steady state levels. Thus the period of maximal polarization of the calcium current coincides with the period during which the developmental polarity of the spores was fixed by gravity. To verify that this polarized movement of calcium was indeed attributable to gravity and not to the intrinsic polarity of the cell, spores were sown in a wire mesh to keep them locked in a fixed orientation. Measurements taken at the top of the spore again revealed a large efflux of calcium. The wire mesh was then "flipped" 1800, and within the 5 minutes it took to establish a new stable recording, the same calcium polarity was reestablished, showing the same high level of efflux at the newly positioned top of the cell. This response was unaffected by shining unidirectional white light at various positions onto the spores thereby eliminating the possibility of light response. To test the specificity of this response for calcium, we utilized an H+ probe and examined the relative flux of H+ ions during the same period of time. The results demonstrate that during the first day after the cells are induced to germinate, the movement of calcium out of the cell is polarized and is strongest in a direction that opposes the vector of gravity. This suggests that while gravity is fixing the polarity of the cells it is also activating calcium pumps along the top and sides of the cell and inducing calcium channels to open along the bottom, resulting in a calcium current that moves from the bottom to the top of the cell. Because the efflux from the top and sides is much greater than the influx from the bottom, some release of internal calcium stores probably participates in sustaining the current. Because this polarized current develops so rapidly after reorientation it is probably one of the earliest cell-level responses induced by gravity and could play an important role in guiding subsequent polar events, such as the downward migration of the nucleus. The fact that the magnitude of the current drops off dramatically after the developmental polarity of the cell has been fixed suggests a probable role for this current in establishing that polarity.

重力可以诱发多种发育事件 以及许多不同种类细胞的生长反应。 怎么单身 细胞感知重力并将这种刺激转换成信号 极化反应仍然是一个谜。 在此我们第一时间报道 有证据表明重力可以使细胞内的流动极化 信号离子、钙进出单个细胞。 角蕨属 是一种水生蕨类植物，能产生大的单细胞孢子。 后 这些孢子的萌发是由光引发的，有 一段有限的时间，通常是 24 小时，在此期间重力可以 修复他们的发展极性。 极性固定结果 细胞核向下迁移，第一平面 细胞分裂的位置不对称且垂直于 重力矢量，并且产生的两种细胞类型以相反的方向生长 方向平行于重力矢量。 调查是否 钙参与了这种极化事件，我们使用了 自参考钙选择性电极（Kuhtreiber 和 Jaffe， 1990）并记录了钙穿过细胞的净运动 萌发后孢子顶部、侧面和底部的膜 被发起。 在顶部观察到钙的强烈流出 孢子在大约 6 小时后急剧增加 开始发芽。 也有钙离子从 孢子侧面，但比顶部流出小 20 倍。 在孢子底部观察到钙的流入，在 2 时达到峰值。 到达顶峰后的几个小时。 观察到钙的移动 仅在发芽后的前 24 小时内，此后 它在所有三个点均下降至较低的稳态水平。 因此 钙电流最大极化周期与 孢子发育极性的时期 由重力固定。 为了验证钙的这种极化运动 确实归因于重力而不是内在的极性 在细胞的内部，孢子被播种在金属丝网上，以将它们锁在一个 固定方向。 再次在孢子顶部进行测量 发现大量的钙外流。 然后金属丝网被“翻转” 1800，5分钟内就建立了新的马厩 记录中，重新建立了相同的钙极性，显示 在新定位的单元顶部具有相同高水平的流出。 该响应不受单向白光照射的影响 孢子上的不同位置，从而消除了可能性 的光响应。 为了测试此响应的特异性 钙，我们使用 H+ 探针并检查 H+ 的相对通量 离子在同一时间段内。 结果表明 在细胞被诱导发芽后的第一天， 钙离开细胞的运动是极化的，并且在 与重力矢量相反的方向。 这表明 虽然重力固定了细胞的极性，但它也固定了细胞的极性。 激活细胞顶部和侧面的钙泵， 诱导钙通道沿底部打开，从而产生 钙电流从细胞底部移动到顶部。 因为从顶部和侧面的流出量远大于从 从底部涌入，释放一些内部钙储备 可能参与维持电流。 因为这个 极化电流在重新定向后发展得如此之快 可能是重力引起的最早的细胞水平反应之一 并可以在指导随后的极地事件中发挥重要作用， 比如细胞核向下迁移。 事实是 电流的幅度急剧下降后 细胞的发育极性已被固定表明可能 该电流在建立极性方面的作用。