Evolution of Potassium Channels and Nerve Networks in Cnidaria

所有动物都有神经系统--由可兴奋细胞组成的组织，它们在身体的不同部位之间传递和整合信息。 神经系统的结构和活动在生物体之间有很大的差异，从相对分散的刺胞动物的神经网络到解剖学上不同的双侧动物的集中神经系统。 然而，所有动物的神经系统的所有细胞都是电反应的。离子通道蛋白质，配体门控的，其响应于突触处的神经递质和突触外调节信号，以及电压门控的，其响应于膜电位的变化，调节膜电位。 该提案描述了一个旨在识别和表征刺胞动物Polyacrylis penicillatus中电压门控钾通道的计划。进化的自然过程产生了大量的同源物，这些同源物在序列上不同，但有一个共同的特性--所有的变体在它们产生的生物体中都是有功能的。 我们建议从P. penicillatus中分离总共15个电压门控钾通道cDNA（除了迄今为止已经分离的6个之外）。 当通道被克隆和测序，我们将单独表达它们在非洲爪蟾卵母细胞，以确定其电生理特性，使用电压钳技术，并比较其序列和活动，从其他生物体的已知通道。 这些比较将使我们能够制定有关蛋白质序列和通道活性之间关系的假设，我们将使用合成诱变和电生理学表征的组合进行测试。 与此同时，我们将为这些通道中的每一个制备抗体，并绘制它们在水母的成年水母中的位置，作为理解刺胞动物神经网和其他生物神经系统之间相似性和差异的第一步。青霉是这些研究的一个很好的选择。 成虫是一种自由生活的水母，与其他刺胞动物模式生物不同，Hydra magnipillatata是一种无柄水螅，Nematostella vectensis是一种无柄海葵。 因此，它的神经系统已经进化成一种能动的而不是固着的生活方式。 它足够大，以至于对其神经系统不同组成部分的电生理学研究已经证明是简单的。 我们对P. penicillatus的神经网络解剖有了全面的了解。 六种不同的电压门控钾通道已经被分离和电生理特性。 这些调查的结果证明了我们对该计划采取的总体方法的可行性、力量和有效性。**

All animals have nervous systems - tissues formed of excitable cells that transmit and integrate information between different parts of the body. The structure and activity of nervous systems varies widely between organisms, from the relatively dispersed neural networks of the Cnidaria to the many anatomically different centralized nervous systems of the Bilateria. However, all cells of the nervous systems of all animals are electrically responsive. Ion channel proteins, both ligand-gated, which respond to neurotransmitters at the synapse and extra-synaptic modulatory signals, and voltage-gated, which respond to changes in membrane potential, modulate the membrane potential. This proposal describes a program aimed at identifying and characterizing the voltage-gated potassium channels in the cnidarian, Polyorchis penicillatus.***The natural process of evolution gives rise to a large number of homologs that differ in sequence but that have one common property - all the variants are functional in the context of the organisms in which they arise. We propose to isolate a total of 15 voltage-gated potassium channel cDNAs from P. penicillatus (in addition to the 6 that have been isolated to date). When the channels are cloned and sequenced we will express them individually in oocytes of Xenopus laevis to determine their electrophysiological properties, using the voltage clamp technique, and compare their sequences and activities to known channels from other organisms. These comparisons will allow us to formulate hypotheses about the relationship between the protein sequences and the activity of the channels, which we will test using a combination of synthetic mutagenesis and electrophysiological characterization. In parallel, we will prepare antibodies to each of these channels and map their locations in the adult medusa of the jellyfish, as a first step towards understanding the similarities and differences between the cnidarian nerve net and nervous systems from other organisms.***P. penicillatus has been a good choice for these studies. The adult form is a free-living medusa, unlike the other cnidarian model organisms, Hydra magnipapillata, a sessile polyp, and Nematostella vectensis, a sessile anemone. Thus, its nervous system has evolved to facilitate a motile rather than sessile life-style. It is large enough that electrophysiological studies on different components of its nervous system have proven straightforward. We have a thorough knowledge of the anatomy of the neural network in P. penicillatus. Six different voltage-gated potassium channels have already been isolated and electrophysiologically characterized. The results from those investigations have demonstrated the feasibility, power and validity of the overall approach that we are taking to this program.**