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[O2-E-PM1-02] Crystal Phase Regulation in Whitlockite-Based Hypermineralized Hard Tissue of Elephant Shark (Callorhinchus milii) Tooth Plate
Keywords:ギンザメ、歯板、結晶成分
The elephant shark (Callorhinchus milii (C. milii), Holocephali, Chondrichthyes) has unique dental organs, i.e., hypermineralized tooth plates. While hypermineralized tissues of bony vertebrates and elasmobranchs consist of hydroxyapatite (HAp: Ca5(PO4)3OH) or fluoroapatite (FAp: Ca5(PO4)3F), mineral component of the hypermineralized tissue in the tooth plate is determined as Mg-containing whitlockite (WH: Ca9MgHPO4(PO4)6) regarding Chimaera phantasma [1, 2]. Since holocephalans diverged from the same ancestor with elasmobranchs, it was speculated on phylogenetic grounds that holocephalans also have mechanism to form HAp or FAp as a tissue component. However, at present, there is little crystallographic study on the hypermineralized tissue of holocephalans.
To verify the above, we examined both embryo and adult of C. milii tooth plates using a high-performance micro-beam X-ray diffraction technique, scanning electron microscope equipped with energy dispersive elemental analyzer, and Fourier transform infrared spectroscopy [3].
As a result, it was revealed that HAp formed in the early stage of the hypermineralized tissue formation; WH formed subsequently and the quantity increased rapidly to become the major phase. Nevertheless, low crystalline HAp was found to form throughout the tissue. The increment of WH synchronized with the increment of Mg in the tissue. Thus, it was suggested that although C. milii had mechanism to form HAp, an excess of Mg promoted formation of WH. Furthermore, presence of low crystalline HAp around WH may relate to hardening of the tissue [2].
Reference
[1] M. Ishiyama, I. Sasagawa, J. Akai (1984) Arch Hist Jap, 47, 89.
[2] M. Iijima, M. Ishiyama (2020) Sci Rep, https://doi.org/10.1038/s41598-020-75545-0.
[3] M. Iijima, et al. (2023) Cryst Growth Des, https://doi.org/10.1021/acs.cgd.2c00820.
To verify the above, we examined both embryo and adult of C. milii tooth plates using a high-performance micro-beam X-ray diffraction technique, scanning electron microscope equipped with energy dispersive elemental analyzer, and Fourier transform infrared spectroscopy [3].
As a result, it was revealed that HAp formed in the early stage of the hypermineralized tissue formation; WH formed subsequently and the quantity increased rapidly to become the major phase. Nevertheless, low crystalline HAp was found to form throughout the tissue. The increment of WH synchronized with the increment of Mg in the tissue. Thus, it was suggested that although C. milii had mechanism to form HAp, an excess of Mg promoted formation of WH. Furthermore, presence of low crystalline HAp around WH may relate to hardening of the tissue [2].
Reference
[1] M. Ishiyama, I. Sasagawa, J. Akai (1984) Arch Hist Jap, 47, 89.
[2] M. Iijima, M. Ishiyama (2020) Sci Rep, https://doi.org/10.1038/s41598-020-75545-0.
[3] M. Iijima, et al. (2023) Cryst Growth Des, https://doi.org/10.1021/acs.cgd.2c00820.