Funt Nir, Palmer Benjamin A, Weiner Steve, Addadi Lia
Department of Structural Biology, Weizmann Institute of Science, Rehovot, 7610001, Israel.
Chempluschem. 2017 Jun;82(6):914-923. doi: 10.1002/cplu.201700151.
Fish-scale iridophore cells deposit guanine crystals and assemble them into multilayer reflectors to produce silvery reflectance. The crystal orientation controls the reflective properties of the fish scales, but little is known about the degree of orientation of the guanine crystals and whether this orientation is pre-determined at the level of an individual cell. Koi fish-scale-attached iridophores, iridophores on regenerated scales, and cultured iridophores were examined by using light microscopy and synchrotron micro-X-ray diffraction. More than 95 % of the thin {100} guanine crystal plates in the iridophores of the mature and regenerated scales are oriented parallel to the scale surface and perpendicular to the direction of the incoming light. More than 70 % of the crystals in cultured iridophore cells are also in this orientation. The crystals are elongated and within each cell on the mature scale and in the cultured cells the long morphological axes are well aligned with the long axis of the iridophore. In contrast to the cultured iridophores, in the mature scale the iridophore cells are co-aligned with each other. Cultured iridophores are flexible and motile, and azimuthal crystal orientations vary as the cells move. We conclude that iridophore cells function as independent units and that the control over crystal orientation is pre-determined at the individual cell level in the direction that is essential for function, namely, exposing the large reflecting crystal surface to light.
鱼鳞虹彩细胞沉积鸟嘌呤晶体，并将它们组装成多层反射器以产生银色反射。晶体取向控制着鱼鳞的反射特性，但对于鸟嘌呤晶体的取向程度以及这种取向是否在单个细胞水平上预先确定，人们知之甚少。通过光学显微镜和同步加速器微X射线衍射对锦鲤鱼鳞附着的虹彩细胞、再生鳞片上的虹彩细胞以及培养的虹彩细胞进行了检查。成熟鳞片和再生鳞片虹彩细胞中超过95%的薄{100}鸟嘌呤晶体板与鳞片表面平行且与入射光方向垂直。培养的虹彩细胞中超过70%的晶体也呈这种取向。晶体在成熟鳞片的每个细胞内以及培养细胞中都呈细长状，其长形态轴与虹彩细胞的长轴良好对齐。与培养的虹彩细胞不同，在成熟鳞片中虹彩细胞彼此共同对齐。培养的虹彩细胞具有灵活性和运动性，随着细胞移动，晶体的方位取向会发生变化。我们得出结论，虹彩细胞作为独立单元发挥作用，并且对晶体取向的控制在单个细胞水平上预先确定，其方向对于功能至关重要，即让大的反射晶体表面暴露于光下。
