Ciona Embryonic Tail Bending Is Driven By Asymmetrical Notochord Contractility And Coordinated By Epithelial Proliferation

Ventral bending of the embryonic tail within the chorion is an evolutionarily conserved morphogenetic event in both invertebrates and vertebrates. However, the complexity of the anatomical structure of vertebrate embryos makes it difficult to experimentally identify the mechanisms underlying embryonic folding. This study investigated the mechanisms underlying embryonic tail bending in chordates. To further understand the mechanical role of each tissue, we also developed a physical model with experimentally measured parameters to simulate embryonic tail bending. Actomyosin asymmetrically accumulated at the ventral side of the notochord, and cell proliferation of the dorsal tail epidermis was faster than that in the ventral counterpart during embryonic tail bending. Genetic disruption of actomyosin activity and inhibition of cell proliferation dorsally caused abnormal tail bending, indicating that both asymmetrical actomyosin contractility in the notochord and the discrepancy of epidermis cell proliferation are required for tail bending. In addition, asymmetrical notochord contractility was sufficient to drive embryonic tail bending, whereas differential epidermis proliferation was a passive response to mechanical forces. These findings showed that asymmetrical notochord contractility coordinates with differential epidermis proliferation mechanisms to drive embryonic tail bending.