Essner Jeffrey J, Amack Jeffrey D, Nyholm Molly K, Harris Erin B, Yost H Joseph
Huntsman Cancer Institute, Center for Children, Department of Oncological Sciences, University of Utah, Salt Lake City, UT 84112, USA.
Development. 2005 Mar;132(6):1247-60. doi: 10.1242/dev.01663. Epub 2005 Feb 16.
Monocilia have been proposed to establish the left-right (LR) body axis in vertebrate embryos by creating a directional fluid flow that triggers asymmetric gene expression. In zebrafish, dorsal forerunner cells (DFCs) express a conserved ciliary dynein gene (left-right dynein-related1, lrdr1) and form a ciliated epithelium inside a fluid-filled organ called Kupffer's vesicle (KV). Here, videomicroscopy demonstrates that cilia inside KV are motile and create a directional fluid flow just prior to the onset of asymmetric gene expression in lateral cells. Laser ablation of DFCs and surgical disruption of KV provide direct evidence that ciliated KV cells are required during early somitogenesis for subsequent LR patterning in the brain, heart and gut. Antisense morpholinos against lrdr1 disrupt KV fluid flow and perturb LR development. Furthermore, lrdr1 morpholinos targeted to DFC/KV cells demonstrate that Lrdr1 functions in these ciliated cells to control LR patterning. This provides the first direct evidence, in any vertebrate, that impairing cilia function in derivatives of the dorsal organizer, and not in other cells that express ciliogenic genes, alters LR development. Finally, genetic analysis reveals novel roles for the T-box transcription factor no tail and the Nodal signaling pathway as upstream regulators of lrdr1 expression and KV morphogenesis. We propose that KV is a transient embryonic 'organ of asymmetry' that directs LR development by establishing a directional fluid flow. These results suggest that cilia are an essential component of a conserved mechanism that controls the transition from bilateral symmetry to LR asymmetry in vertebrates.
有人提出，单纤毛通过产生定向的液流来触发不对称基因表达，从而在脊椎动物胚胎中建立左右（LR）体轴。在斑马鱼中，背侧前体细胞（DFC）表达一种保守的纤毛动力蛋白基因（左右动力蛋白相关1，lrdr1），并在一个称为库普弗囊泡（KV）的充满液体的器官内形成纤毛上皮。在这里，视频显微镜显示，在侧向细胞中不对称基因表达开始之前，KV内的纤毛是运动的，并产生定向的液流。对DFC进行激光消融和对KV进行手术破坏提供了直接证据，表明在早期体节形成过程中，具有纤毛的KV细胞是随后大脑、心脏和肠道LR模式形成所必需的。针对lrdr1的反义吗啉代寡核苷酸破坏了KV的液流并扰乱了LR发育。此外，靶向DFC/KV细胞的lrdr1吗啉代寡核苷酸表明，Lrdr1在这些具有纤毛的细胞中发挥作用以控制LR模式形成。这在任何脊椎动物中都提供了第一个直接证据，即损害背侧组织者衍生物中的纤毛功能，而不是其他表达纤毛生成基因的细胞中的纤毛功能，会改变LR发育。最后，遗传分析揭示了T盒转录因子无尾和Nodal信号通路作为lrdr1表达和KV形态发生的上游调节因子的新作用。我们提出，KV是一个短暂的胚胎“不对称器官”，它通过建立定向的液流来指导LR发育。这些结果表明，纤毛是一种保守机制的重要组成部分，该机制控制脊椎动物从双侧对称到LR不对称的转变。
