Okamura Yasushi, Nishino Atsuo, Murata Yoshimichi, Nakajo Koichi, Iwasaki Hirohide, Ohtsuka Yukio, Tanaka-Kunishima Motoko, Takahashi Nobuyuki, Hara Yuji, Yoshida Takashi, Nishida Motohiro, Okado Haruo, Watari Hirofumi, Meinertzhagen Ian A, Satoh Nori, Takahashi Kunitaro, Satou Yutaka, Okada Yasunobu, Mori Yasuo
Section of Developmental Neurophysiology, Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, Okazaki, Aichi, Japan.
Physiol Genomics. 2005 Aug 11;22(3):269-82. doi: 10.1152/physiolgenomics.00229.2004. Epub 2005 May 24.
Ion fluxes through membrane ion channels play crucial roles both in neuronal signaling and the homeostatic control of body electrolytes. Despite our knowledge about the respective ion channels, just how diversification of ion channel genes underlies adaptation of animals to the physical environment remains unknown. Here we systematically survey up to 160 putative ion channel genes in the genome of Ciona intestinalis and compare them with corresponding gene sets from the genomes of the nematode Chaenorhabditis elegans, the fruit fly Drosophila melanogaster, and the more closely related genomes of vertebrates. Ciona has a set of so-called "prototype" genes for ion channels regulating neuronal excitability, or for neurotransmitter receptors, suggesting that genes responsible for neuronal signaling in mammals appear to have diversified mainly via gene duplications of the more restricted members of ancestral genomes before the ascidian/vertebrate divergence. Most genes responsible for modulation of neuronal excitability and pain sensation are absent from the ascidian genome, suggesting that these genes arose after the divergence of urochordates. In contrast, the divergent genes encoding connexins, transient receptor potential-related channels and chloride channels, channels involved rather in homeostatic control, indicate gene duplication events unique to the ascidian lineage. Because several invertebrate-unique channel genes exist in Ciona genome, the crown group of extant vertebrates not only acquired novel channel genes via gene/genome duplications but also discarded some ancient genes that have persisted in invertebrates. Such genome-wide information of ion channel genes in basal chordates enables us to begin correlating the innovation and remodeling of genes with the adaptation of more recent chordates to their physical environment.
离子通过膜离子通道的流动在神经元信号传导和身体电解质的稳态控制中都起着至关重要的作用。尽管我们对各自的离子通道有所了解，但离子通道基因的多样化如何构成动物对物理环境的适应性仍不清楚。在这里，我们系统地调查了海鞘基因组中多达160个假定的离子通道基因，并将它们与线虫秀丽隐杆线虫、果蝇黑腹果蝇以及更密切相关的脊椎动物基因组中的相应基因集进行比较。海鞘有一组用于调节神经元兴奋性的离子通道或神经递质受体的所谓“原型”基因，这表明哺乳动物中负责神经元信号传导的基因似乎主要是通过在海鞘/脊椎动物分化之前祖先基因组中更有限成员的基因复制而多样化的。海鞘基因组中不存在大多数负责调节神经元兴奋性和痛觉的基因，这表明这些基因是在尾索动物分化之后出现的。相比之下，编码连接蛋白、瞬时受体电位相关通道和氯离子通道的差异基因，这些通道更多地参与稳态控制，表明是海鞘谱系特有的基因复制事件。由于海鞘基因组中存在几个无脊椎动物特有的通道基因，现存脊椎动物的冠群不仅通过基因/基因组复制获得了新的通道基因，还丢弃了一些在无脊椎动物中一直存在的古老基因。基础脊索动物中离子通道基因的这种全基因组信息使我们能够开始将基因的创新和重塑与更近的脊索动物对其物理环境的适应性联系起来。
