Yoshida Keita, Saiga Hidetoshi
Department of Biological Science, Graduate School of Science and Engineering, Tokyo Metropolitan University, 1-1 Minamiohsawa, Hachiohji, Tokyo, Japan.
Dev Genes Evol. 2008 Jul;218(7):353-60. doi: 10.1007/s00427-008-0230-3. Epub 2008 Jun 11.
Left-right asymmetric expression of Pitx as well as of Nodal has been observed in some ascidian species, but a mechanism that regulates the asymmetric expression of Pitx remains largely unclear. We addressed the transcription regulatory mechanism of the left-right asymmetric expression of Pitx gene in the ascidian, Ciona intestinalis. We first identified an intronic enhancer that drives Ci-Pitx left-sided expression in the epidermis and found that a single FoxH1 binding site present in this enhancer is essential for its activity. Also, we have shown that the enhancer requires Nodal signaling to drive the Ci-Pitx expression in the left epidermis. In C. intestinalis, left-sided expression of the Nodal gene has not been reported so far. We have confirmed that Ci-Nodal is expressed in the left epidermis of embryos at the tailbud stage only when they are allowed to develop within the chorion. Then, to test the importance of the FoxH1 binding site, we carried out knock down experiments using morpholino antisense oligonucleotides against Ci-FoxHa, the only FoxH gene that is expressed in the same stage as the left-sided expression of Ci-Pitx is observed. Knocking down of the function of Ci-FoxHa led to the down regulation of the expression of Ci-Pitx in the left epidermis. The present results suggest that the regulatory mechanism controlling the left-right asymmetric expression of the Pitx genes is well conserved between C. intestinalis and vertebrates.
在一些海鞘物种中已观察到Pitx以及Nodal的左右不对称表达，但调节Pitx不对称表达的机制仍不清楚。我们研究了海鞘Ciona intestinalis中Pitx基因左右不对称表达的转录调控机制。我们首先鉴定了一个内含子增强子，它驱动Ci-Pitx在表皮中的左侧表达，并发现该增强子中存在的单个FoxH1结合位点对其活性至关重要。此外，我们还表明该增强子需要Nodal信号来驱动Ci-Pitx在左侧表皮中的表达。在C. intestinalis中，迄今为止尚未报道Nodal基因的左侧表达。我们已经证实，只有当胚胎在绒毛膜内发育时，Ci-Nodal才在尾芽期胚胎的左侧表皮中表达。然后，为了测试FoxH1结合位点的重要性，我们使用针对Ci-FoxHa的吗啉代反义寡核苷酸进行了敲低实验，Ci-FoxHa是在观察到Ci-Pitx左侧表达的同一阶段表达的唯一FoxH基因。敲低Ci-FoxHa的功能导致Ci-Pitx在左侧表皮中的表达下调。目前的结果表明C. intestinalis和脊椎动物之间控制Pitx基因左右不对称表达的调控机制高度保守。
