Department of Biosciences and Informatics, Faculty of Science and Technology Keio University, Tokyo, Japan
Among the expectations of the field of regenerative medicine in recent years, it is recognized that elucidation of three-dimensional organ formation mechanism is increasingly important. In particular, there are tube tissues in our body, but little is known about how they are formed. Therefore, since the Ciona notochord is a simple in vivo model for tubulogenesis. We studied on elucidation of the mechanism of the Ciona notochor tubulogenesis by the methods of chemical biology. First, we searched for compounds that affect the early development of Ciona intestinalis, and we found that the cancer cell migration inhibitor UTKO1 selectively inhibits Ciona notochord tubulogenesis. We have reported that the target molecule of UTKO1 in human cancer cells is 14-3-3. Therefore, we examined whether UTKO1 acts on 14-3-3 also in ascidian. It has been found that UTKO1 inhibits tube formation by specifically binding to 14-3-3 εa and suppressing its function. We also found that 14- 3-3 εa directly interacts with the chordally expressed Ezrin / Radixin / Moesin (ERM). Both proteins were colocalized to the contraction ring of the basal domain, and UTKO1 inhibited direct interaction of 14-3-3εa-ERM and canceled colocalization of contractile ring. Next, we conducted a live imaging of the tube formation process to analyze how the interaction between 14-3-3εa and ERM controls tube formation. Before the opening of the lumen, 14-3-3εa and ERM co-localized in the contractile ring, and when the lumen was opened, they traveled to the lumen along the "flow" periodically generated from the contraction ring toward the lumen. This "flow" was not found in UTKO1-treated ascidians or mutant ascidians that lost the binding ability of 14-3-3εa to ERM. From the above, we proposed that the interaction in the contraction ring of 14-3-3 εa-ERM produces directed flow and contributes to transport of an important factor required for the tube formation from the basal domain to the apical domain.