Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Tokyo 184-8588, Japan.
Developmental Genetics Group, Graduate School of Frontier Biosciences, Osaka University, Osaka 565-0871, Japan.
Cold Spring Harb Perspect Biol. 2017 Oct 3;9(10):a028282. doi: 10.1101/cshperspect.a028282.
Visceral organs of vertebrates show left-right (L-R) asymmetry with regard to their position and morphology. Cilia play essential role in generating L-R asymmetry. A number of genes required for L-R asymmetry have now been identified in vertebrates, including human, many of which contribute to the formation and motility of cilia. In the mouse embryo, breaking of L-R symmetry occurs in the ventral node, where two types of cilia (motile and immotile) are present. Motile cilia are located at the central region of the node, and generate a leftward fluid flow. These motile cilia at the node are unique in that they rotate in the clockwise direction, unlike other immotile cilia such as airway cilia that show planar beating. The second type of cilia essential for L-R asymmetry is immotile cilia that are peripherally located immotile cilia. They sense a flow-dependent signal, which is either chemical or mechanical in nature. Although Ca signaling is implicated in flow sensing, the precise mechanism remains unknown.
脊椎动物的内脏器官在位置和形态上表现出左右（L-R）不对称。纤毛在产生 L-R 不对称中发挥着重要作用。目前已在脊椎动物中鉴定出许多与 L-R 不对称相关的基因，其中许多基因参与纤毛的形成和运动。在小鼠胚胎中，L-R 对称性的破坏发生在腹节，腹节中存在两种纤毛（运动和非运动）。运动纤毛位于节点的中央区域，产生向左的液流。这些位于节点的运动纤毛的独特之处在于它们顺时针旋转，与其他非运动纤毛（如气道纤毛）的平面拍打不同。另一种对 L-R 不对称至关重要的纤毛是非运动纤毛，它们位于节点的周边。它们感知依赖于流动的信号，该信号在本质上是化学的或机械的。尽管 Ca 信号转导参与了流动感应，但精确的机制仍不清楚。
