The crystalline phase of cellulose changes under developmental control in a marine chordate
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The native form of cellulose is a fibrillar composite of two crystalline phases, the triclinic Iα and monoclinic Iβ allomorphs. Allomorph ratios are species-specific, and this gives rise to natural structural variations in cellulose crystals. However, the mechanisms contributing to crystal formation remain unknown. We show that the two crystalline phases of cellulose are tailored to distinct structures during different developmental stages of the tunicate chordate Oikopleura dioica. Larval cellulose consisting of Iα allomorph constitutes the body cuticle fin, whereas adult cellulose consisting of Iβ allomorph frames a mucous filter-feeding device, the “house.” Both structures are secreted from the epidermis in accordance with the mutually exclusive expression patterns of two distinct putative cellulose synthase genes. We discuss a possible linkage between structural variations of the crystalline phases of cellulose and the underlying evolutionary genetics of cellulose biosynthesis.
KeywordsCellulose Allomorph Tunicate Appendicularian Oikopleura dioica
We thank Dr. Tomoya Imai for valuable discussion, Dr. Yutaka Satou for the qPCR facility, Prof. Hiroyuki Yano for the FE-SEM facility, Dr. Fuki Gyoja for sampling Molgula tectiformis, and staff members of the Misaki Marine Biological Station, University of Tokyo, and Seto Marine Biological Station, Kyoto University, for sampling Oikopleura longicauda and Oikopleura dioica, respectively. The nucleotide sequences for the reported genes have been deposited with the GenBank under accession codes AB543594 (Od-CesA1) and AB543593 (Od-CesA2). K.N. designed research, performed experiments, and wrote the manuscript. A.N. performed collection, culture, and preparation of appendicularians. Y.H. and J.S. performed electron diffraction and FTIR microscopy. E.H. performed transmission electron microscopy. N.S. supervised reseach. All authors discussed the results and commented on the manuscript. The authors declare no competing financial interests. This work was supported by Grants-in-Aid for Young Scientists to K.N. (no. 18770046 and 21780166) and Grant-in-Aid to N.S. (no. 17018018) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan. This work was also partly supported by Intellectual Cluster Formation of Okinawa Prefecture, Japan.
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