Shimeld Sebastian M, Levin Michael
Department of Zoology, University of Oxford, Oxford, United Kingdom.
Dev Dyn. 2006 Jun;235(6):1543-53. doi: 10.1002/dvdy.20792.
Vertebrate embryos develop distinct left-right asymmetry under the control of a conserved pathway involving left-sided deployment of the nodal and Pit x 2 genes. The mechanism that initiates asymmetric expression of these genes is less clear, with cilia, ion flux, and signalling molecules all implicated. Vertebrates share the chordate phylum with urochordates such as the sea squirt Ciona intestinalis. We have explored the role of ion flux in regulating left-right asymmetry in Ciona, using an assay in which perturbation of left-sided Ci-Pitx expression provides a read-out for the disruption of asymmetry. Our data show that omeprazole, which specifically inhibits H(+)K(+)ATPase activity, disrupts asymmetry in Ciona. The vertebrate H(+)K(+)ATPase is composed of two subunits, alpha and beta. We identified one Ciona beta ortholog and two Ciona alpha orthologs of the vertebrate H(+)K(+)ATPase genes, and show that one of these is expressed in dorsal and ventral embryonic midline cells shortly before the activation of left-sided Ci-Pitx expression. Furthermore, we show that omeprazole exerts its effect on asymmetry at this point in development, and additionally implicate K(+) channels in the regulation of asymmetry in Ciona. These experiments demonstrate a role for ion flux in the regulation of asymmetry in Ciona, and show a conserved, ancestral role for the H(+)K(+)ATPase ion pump in this process.
脊椎动物胚胎在涉及结节基因和Pitx 2基因左侧分布的保守信号通路控制下发育出明显的左右不对称性。启动这些基因不对称表达的机制尚不清楚，纤毛、离子流和信号分子都与之有关。脊椎动物与尾索动物（如海鞘）同属脊索动物门。我们利用一种检测方法，即通过干扰左侧Ci-Pitx表达来反映不对称性的破坏，探索了离子流在海鞘左右不对称性调节中的作用。我们的数据表明，特异性抑制H(+)K(+)ATP酶活性的奥美拉唑会破坏海鞘的不对称性。脊椎动物的H(+)K(+)ATP酶由α和β两个亚基组成。我们鉴定出了脊椎动物H(+)K(+)ATP酶基因的一个海鞘β直系同源基因和两个海鞘α直系同源基因，并表明其中一个在左侧Ci-Pitx表达激活前不久在胚胎背侧和腹侧中线细胞中表达。此外，我们表明奥美拉唑在发育的这一阶段对不对称性产生影响，并且还表明钾离子通道参与了海鞘不对称性的调节。这些实验证明了离子流在海鞘不对称性调节中的作用，并表明H(+)K(+)ATP酶离子泵在这一过程中具有保守的、祖先性的作用。
