For the whole embryo, polarity manifests as the formation of orientated body axis and the asymmetric location of organs. At the tissue level, polarity appears as asymmetric differentiation forming distinct cell types and/or the mechanically anisotropic tissues. Polarity widely exists during the entire lifespan and at all levels of an organism. However, these processes are not always isotropic, and anisotropic processes lead to spatial differences in cell shape and structure, directed cell behaviors (e.g., migration, mitosis, adhesion, secretion, and signaling transition), and asymmetric subcellular structures (e.g., organelle localization and cytoskeleton distribution) all of which generate what is called “polarity” ( Dhonukshe, 2013 Wolpert, 2013). In addition, the notochord’s mechanical properties are associated with polarity establishment and transformation, which bridge signaling regulation and tissue mechanical properties that enable the coordinated organogenesis during embryo development.Ĭell proliferation, migration, and deformation extracellular matrix (ECM) secretion and cell–cell junction formation and remodeling are basic processes in tissue and organ architecture establishment during embryogenesis. Some cytoskeleton polarity patterns are a consequence of PCP: however, an additional polarized cytoskeleton, together with Rho signaling, might serve as a guide for correct AB polarity initiation in the notochord. Cytoskeleton distribution is one of the main downstream events of cell polarity. Subsequently, the notochord undergoes a mesenchymal-epithelial transition, becoming an unusual epithelium in which cells have two opposing apical domains facing the extracellular lumen deposited between adjacent notochord cells controlled by apical-basal (AB) polarity. At the early stage, planar cell polarity (PCP) is initialized, which drives cell convergence extension and migration to form a rod-like structure. This review summarizes cellular and tissue-level polarities during notochord development in ascidians. The notochord is a characteristic midline organ in chordate embryos that supports the body structure and produces positioning signaling. 3Institute of Evolution and Marine Biodiversity, Ocean University of China, Qingdao, ChinaĬell and tissue polarity due to the extracellular signaling and intracellular gene cascades, in turn, signals the directed cell behaviors and asymmetric tissue architectures that play a crucial role in organogenesis and embryogenesis.2Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, China.1Sars-Fang Centre, MoE Key Laboratory of Marine Genetics and Breeding, College of Marine Life Sciences, Ocean University of China, Qingdao, China.Hongzhe Peng 1, Runyu Qiao 1 and Bo Dong 1,2,3*
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