The initial breaking of left-right (L–R) symmetry in the embryo is controlled by a motile-cilia-driven leftward fluid flow in the left-right organiser (LRO), resulting in L–R asymmetric gene expression flanking the LRO. Ultimately this results in left- but not right-sided activation of the Nodal-Pitx2 pathway in more lateral tissues. While aspects of the initial breaking event clearly vary between vertebrates, events in the Lateral Plate Mesoderm (LPM) are conserved through the vertebrate lineage. Evidence from model systems and humans highlights the role of cilia both in the initial symmetry breaking and in the ability of more lateral tissues to exhibit asymmetric gene expression. In this review we concentrate on the process of L–R determination in mouse and humans.

胚胎中左右（L-R）对称性的最初打破是由左右组织器（LRO）中运动纤毛驱动的向左流体流动控制的，导致 LRO 侧翼的 L-R 不对称基因表达。最终，这导致更多外侧组织中Nodal - Pitx2通路的左侧激活，但右侧不激活。虽然初始断裂事件的各个方面在脊椎动物之间明显不同，但侧板中胚层 (LPM) 中的事件在整个脊椎动物谱系中都是保守的。来自模型系统和人类的证据强调了纤毛在初始对称性破坏和更多横向组织表现出不对称基因表达的能力中的作用。在这篇综述中，我们重点关注小鼠和人类的 L-R 测定过程。