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Zoological Science
Abstract
Most ascidian species settle on underwater substrates during a short free-swimming tadpole larval period. During this process, “rapid adhesion” occurs on adhesive papillae located at the anterior region of the cephalenteron. Settled and transformed ascidians subsequently expand the attachment area by “slow adhesion” with ampullae. In the present study, we attempted to identify the ultrastructures related to the adhesion process and adhesive materials in the ascidian tunic and to elucidate the biological function of vanadium in adhesion. We focused on an adhesive organ named the adhesive projection, which is newly generated by the adhered tunic to enlarge the bonding area between ascidian and substrate. Based on its structure and the presence of vanadiumcontaining blood cells, the adhesive projection was considered to be a large tunic vessel. At the adhered tunic, eosinophilic regions and migrated tunic cells were observed, but metal deposition was not detected. We speculate that the eosinophilic materials were components of the adhesive glue, and these are likey produced in epithelial cells, tunic cells, or both. Furthermore, using imaging mass spectrometry, we identified eight tunic-specific molecules as glue candidates.
We are deeply grateful to Dr. H. Michibata for valuable advice on conducting experiments. We express our thanks to Dr. T. Harada, the staff of natural science center for basic research and development, Hiroshima University for support to operate iMScope and Dr. Y. Kobayashi, research associate of graduate school of integrated arts and sciences, Hiroshima University for support to make frozen section. We also thank to Mr. Y. Ishitobi, the staff at the Technical Center, Hiroshima University for cooperation to machining the stages of Cryo-TEM. This work was supported in part by Grants-in-Aid from the Ministry of Education, Culture, Sports, Science and Technology of Japan (#15H00451 and #26924014 to N.Y.; #25120508 and #25440170 to T.U.).
The authors declare that they have no competing interests.
TU and NY were involved in all experiments. KK performed transmission electron microscopy. IF performed cryo-cracking, scanning electron microscopy and imaging of element distribution analyses. TU and NY designed the work and prepared the manuscript. All authors read and approved the final manuscript.
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