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Mie, Japan

Nagai K.,K. Mikimoto and Co.
Zoological Science | Year: 2013

During the 18th and 19th centuries, studies of how pearls are formed were conducted mainly in Europe. The subsequent pearl culturing experiments conducted worldwide in the early 20th century, however, failed to develop into a pearl industry. In Japan, however, Kokichi Mikimoto succeeded in culturing blister pearls in 1893 under the guidance of Kakichi Mitsukuri, a professor at Tokyo Imperial University (now the University of Tokyo) and the first director of the Misaki Marine Biological Station, Graduate School of Science, University of Tokyo. This success and subsequent developments laid the foundation for the pearl farming industry, developed new demand for cultured pearls in the European jewelry market, and initiated the full-scale industrialization of pearl culturing. In addition, research at the Misaki Marine Biological Station resulted in noteworthy advances in the scientific study of pearl formation. Today, pearls are cultured worldwide, utilizing a variety of pearl oysters. The pearl farming industry, with its unique origins in Japan, has grown into a global industry. Recently, the introduction of genome analysis has allowed cultured pearl research to make rapid progress worldwide in such areas as the dynamics of mother-of-pearl layer formation and biomineralization. This signals another new era in the study of pearls. © 2013 Zoological Society of Japan.

Basti L.,Tokyo University of Marine Science and Technology | Nagai K.,K. Mikimoto and Co. | Tanaka Y.,Tokyo University of Marine Science and Technology | Segawa S.,Tokyo University of Marine Science and Technology
Marine Biology | Year: 2013

Blooms of the toxic dinoflagellate Heterocapsa circularisquama cause massive bivalve kills in Japan. Mariculture of the Japanese pearl oyster, Pinctada fucata martensii, is the industry most affected by these blooms, especially in Ago Bay, Mie Prefecture, where they are frequent, cause mass mortality of oysters, and overlap with their spawning season. The goal of this August 2009 study was to assess the effects of a toxic strain of H. circularisquama isolated from Ago Bay on gametes, fertilization, and embryo development of pearl oysters. Spermatozoa, eggs, spermatozoa and eggs, and fertilized eggs of pearl oysters from Ago Bay were exposed to H. circularisquama at cell densities reported during the bloom (10-104 cells mL-1) for different periods of time. The concentration of H. circularisquama, exposure duration, and their interactions all had significant effects on gamete quality, fertilization, and embryo development. The motility and swimming velocity of spermatozoa, egg viability, fertilization, and embryo development rate were significantly reduced in all concentrations, with a cell density of 10 cells mL-1 determined to be the critical density of H. circularisquama for deleterious effects. This is the first evidence of inimical effects of an HAB species on bivalve spermatozoa upon direct exposure. Further field and laboratory studies are required to investigate the potential effects of H. circularisquama blooms on the reproduction and recruitment of Japanese pearl oysters and other bivalves. © 2012 Springer-Verlag Berlin Heidelberg.

Awaji M.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Yamamoto T.,K. Mikimoto and Co. | Kakinuma M.,Mie University | Nagai K.,K. Mikimoto and Co. | Watabe S.,Kitasato University
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2014

A method of forming pearls by transplanting outer epithelial cells (OEC) isolated from the mantle of pearl oyster Pinctada fucata was investigated. Two methods, 1) injection of OEC around the pearl nucleus inserted beforehand and 2) insertion of the pearl nucleus carrying a small pit inoculated with OEC, were compared in terms of performance. As a result, method 2 had a higher pearl formation rate than method 1.With method 2, about 70% of the inserted nuclei formed the nacreous layer when OEC were inoculated at 1×104cells/nucleus. Next, OEC isolated from two types of pearl oyster that significantly differed in color (yellowness) of the shell nacre were mixed at four different ratios, and the prepared OEC mixtures were transplanted by method 2 to investigate the effects of the blend on the yellowness of harvested pearls. The yellowness of harvested pearls differed significantly in accordance with the mixing ratio.

Funabara D.,Mie University | Ohmori F.,University of Tokyo | Kinoshita S.,University of Tokyo | Koyama H.,University of Tokyo | And 10 more authors.
PLoS ONE | Year: 2014

In our previous publication, we identified novel gene candidates involved in shell formation by EST analyses of the nacreous and prismatic layer-forming tissues in the pearl oyster Pinctada fucata. In the present study, 14 of those genes, including two known genes, were selected and further examined for their involvement in shell formation using the RNA interference. Molecular characterization based on the deduced amino acid sequences showed that seven of the novel genes encode secretory proteins. The tissue distribution of the transcripts of the genes, as analyzed by RT-PCR and in situ hybridization, was mostly consistent with those obtained by the EST analysis reported previously. Shells in the pearl oysters injected with dsRNAs targeting genes 000027, 000058, 000081, 000096, 000113 (nacrein), 000118, 000133 and 000411(MSI60), which showed expression specific to the nacreous layer forming tissues, showed abnormal surface appearance in this layer. Individuals injected with dsRNAs targeting genes 000027, 000113 and 000133 also exhibited abnormal prismatic layers. Individuals injected with dsRNAs targeting genes 000031, 000066, 000098, 000145, 000194 and 000200, which showed expression specific to prismatic layer forming tissues, displayed an abnormal surface appearance in both the nacreous and prismatic layers. Taken together, the results suggest that the genes involved in prismatic layer formation might also be involved in the formation of the nacreous layers. © 2014 Funabara et al.

Yamasaki Y.,Nagasaki University | Zou Y.,Nagasaki University | Go J.,K. Mikimoto and Co. | Shikata T.,Graduate University for Advanced Studies | And 7 more authors.
Journal of Sea Research | Year: 2011

We used bi-algal culture experiments to investigate and verify the roles of growth interaction between Heterocapsa circularisquama and Prorocentrum dentatum in monospecific bloom formation. Growth of H. circularisquama was slightly inhibited when inoculated at 102cellsmL-1 along with P. dentatum at 104cellsmL-1. In other combinations of inoculation densities, P. dentatum density rapidly decreased to extremely low levels in the presence of H. circularisquama. We used a mathematical model to simulate growth and interactions of H. circularisquama and P. dentatum in bi-algal cultures. The model indicates that one species will always inhibit the growth of the other and that the relative initial cell densities of the species are critical in determining the outcome. When cultured together under conditions without cell contact, growth of H. circularisquama and P. dentatum was not inhibited. As with P. dentatum, the growth of Heterosigma akashiwo and Skeletonema costatum was inhibited in intact cell suspensions with H. circularisquama, but a nontoxic species, Heterocapsa triquetra, did not affect the growth of P. dentatum or the other species. Similarly, cell suspensions of H. circularisquama showed hemolytic activity toward rabbit erythrocytes, but those of H. triquetra did not. In addition, the cell-free supernatant of H. circularisquama cultures showed no significant hemolytic activity. These results suggest that H. circularisquama causes lethality in P. dentatum by direct cell contact in which live-cell-mediated hemolytic activity might be a contributing factor. © 2010 Elsevier B.V.

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