Do multipotential neuronal stem cells use connexin-based channels to coordinate their proliferation and differentiation?

神经系统由数十亿个神经细胞和支持细胞组成，由一层薄薄的、卷曲的自我复制干细胞组成，在早期胚胎中，这些干细胞被组装在一个单一的层面上，就像密集人群中不同形状和身高的人一样。它们在经历一个重复的步骤循环时会改变形状，这个循环会把一个细胞变成两个，最后把几千个细胞变成数十亿。每个细胞总是坐在‘地板’(卷起的薄片的内表面)上，然后将它的DNA和整个身体分裂成两个相同的部分。然后，每个新的细胞都会高高地站立起来，在复制每条染色体之前，将其遗传的DNA包(细胞的细胞核)移到离地面很高的地方。然后，它坐下来再次分裂，重复这个循环，每天最多三次。我们不知道是什么控制了这些上下运动，尽管它们总是与细胞分裂的步骤相匹配。我们可以看到，细胞核以小跳跃的形式运动，这通常与细胞内钙脉冲释放的时间相匹配。我们还知道，钙脉冲可以从一个细胞传递到另一个细胞，从而使一个簇中的每个细胞核一起跳跃；我们有一些证据表明，这些细胞一起经历整个周期，站着和坐着，就像一个花样游泳团队的成员。脉冲通过不同的途径在细胞之间传递，我们打算研究以不同方式使用相同蛋白质(连接蛋白)的两条途径。其中一条途径是钙离子通过被称为缝隙连接的分子对接端口在细胞之间传递，缝隙连接是由六个连接蛋白在每个细胞壁的一个环中组成的。(这就像一名宇航员从对接的航天飞机上漂浮进入空间站)。另一种途径更为复杂：一个细胞中的钙脉冲会导致一种名为ATP的小分子从没有对接的短暂打开的半连接中喷出，进入周围的液体，然后这个ATP与附近细胞上的外部传感器结合，触发内部的另一种钙脉冲。我们可以使用几种药物和DNA相关的分子‘扳手’来改变这些脉冲的传播。其中一些影响两条路线，而另一些只影响一条，这将帮助我们找出哪个更重要，以及它是如何控制的。随着胚胎的生长，一些细胞会以一种特殊的方式分裂，这会让每一半走上不同的职业道路。一个继续分裂，而另一个离开复制的人群，在更高的‘地板’上占据一个位置，成为神经细胞(神经元)，永远不会再分裂。它的细胞核也在与钙脉冲相关的跳跃中运动，我们有新的证据，这需要得到证实，抑制这些脉冲可以阻止细胞离开，这样它就会成为错误位置的神经元。在年轻的神经元中，一种名为中心体的结构就像一艘微小的拖船，用分子绳(微管)拉着细胞核。这在复制细胞的上下运动中可能会发生，也可能不会发生，找出它是否会发生将有助于我们更多地了解它们的运动。我们可以在活细胞的中心体上加一个荧光标签，然后在显微镜下观察它。如果它没有开始拖着细胞核前进，直到细胞停止复制并成为神经元，我们就可以利用这一点来区分复制细胞和年轻神经元，并在显微镜下直接比较它们对药物的反应。我们还可以在细胞对治疗有反应后使用抗体来识别它们，并显示出细胞核和中心体。这两种方法都将帮助我们弄清楚，控制钙脉冲的药物和DNA工具是能够让复制细胞以制造神经元的特殊方式分裂，还是只能在分裂后改变它们的运动模式。这些答案将允许我们设计进一步的实验，在这些实验中，我们可以更深入地研究控制神经元数量和位置的机制，并将它们组织成处理视觉信息的电路。

The nervous system, with its billions of nerve cells and support cells, is built from a thin, rolled sheet of self-replicating stem cells which, in the early embryo, are packed together on a single level like people of differing shapes and heights in a dense crowd. They change shape as they go through a repeated cycle of steps that turns one cell into two, and thousands eventually into billions. Each cell always sits down on the 'floor' (the inner surface of the rolled sheet) before splitting its DNA and then its whole body, into two identical parts. Each new cell then stands up tall, moving its inherited package of DNA (the cell's nucleus) high off the 'floor' before making an exact copy of every chromosome. Then it sits down to divide again, repeating this cycle up to three times a day. We do not know what controls these up-down motions, although they always match the steps in cell division. We can see that the nucleus moves in small jumps, which often match the times when pulses of calcium are released inside the cell. We also know that calcium pulses can be passed from cell to cell so that every nucleus in a cluster jumps together; and we have some evidence that these cells go through whole cycles together, standing and sitting like members of a synchronized swimming team. Pulses pass between cells by various routes and we intend to study two routes that use the same protein (a 'connexin') in different ways. One route involves calcium passing from cell to cell through a molecular docking port called a gap junction, made of six connexins in a ring in each cell's wall. (This is like an astronaut floating into the space station from a docked shuttle). The other route is more complex: a calcium pulse in one cell causes a small molecule called ATP to be spewed out of undocked, briefly opened half-junctions into the surrounding fluid, and this ATP then binds to an external sensor on a nearby cell, triggering another calcium pulse inside. We can use several drugs and DNA-related molecular 'spanners in the works' to change the spread of these pulses. Some of them affect both routes but others only affect one, which will help us find out which is more important and how it is controlled. As the embryo grows, some cells split in a special way which sends each half on a different career path. One carries on dividing, while the other leaves the replicating crowd and takes up a position on a higher 'floor' to become a nerve cell (neuron) and never divides again. Its nucleus, too, moves in jumps associated with calcium pulses, and we have new evidence, which needs to be confirmed, that suppressing these pulses can stop the cell leaving, so that it becomes a neuron in the wrong place. In a young neuron, a structure called the centrosome acts like a tiny tugboat to pull the nucleus along by molecular ropes (microtubules). This may or may not happen in the up-down movement of replicating cells, and finding out whether it does will help us understand more about their movement. We can add a fluorescent tag to the centrosome of a living cell and watch it under a microscope. If it does not begin to tug the nucleus along until the cell has stopped replicating and become a neuron, we can to use this to distinguish replicating cells from young neurons and compare their responses to drugs directly, under the microscope. We can also use antibodies to identify the cells after they have responded to treatment, and show up the nucleus and centrosome. Both approaches will help us to work out whether drugs and DNA tools that control calcium pulses are capable of making replicating cells divide in the special way that makes neurons, or capable only of changing their movement patterns after they have divided. The answers will allow us to design further experiments in which we can look more deeply into the mechanisms that control the numbers and positions of neurons and organize them into circuits that process visual information.