Wu X, Bowers B, Wei Q, Kocher B, Hammer J A
Laboratory of Cell Biology, Section on Molecular Cell Biology, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892-0301, USA.
J Cell Sci. 1997 Apr;110 ( Pt 7):847-59. doi: 10.1242/jcs.110.7.847.
Mice with mutations at the dilute locus exhibit a 'washed out' or 'diluted' coat color. The pigments that are responsible for the coloration of mammalian hair are produced by melanocytes within a specialized organelle, the melanosome. Each melanocyte is responsible for delivering melanosomes via its extensive dendritic arbor to numerous keratinocytes, which go on to form the pigmented hair shaft. In this study, we show by light immunofluorescence microscopy and immunoelectron microscopy that the myosin V isoform encoded by the dilute locus associates with melanosomes. This association, which was seen in all mouse melanocyte cell lines examined and with two independent myosin V antibodies, was evident not only within completely melanized cells, but also within cells undergoing the process of melanosome biogenesis, where coordinate changes in the distributions of a melanosome marker and myosin V were seen. To determine where myosin V, a known actin-based motor, might play a role in melanosome transport, we also examined the cellular distribution of F-actin. The only region where myosin V and F-actin were both concentrated was in dendrites and dendritic tips, which represent the sole destination for melanosomes and where they accumulate in cultured melanocytes. These results support the idea that myosin V serves as the motor for the outward movement of melanosomes within dendritic extensions, and, together with the available information regarding the phenotype of mutant melanocytes in vitro, argue that coat color dilution is caused by the absense of this myosin V-dependent melanosome transport system.
在稀释位点发生突变的小鼠表现出“褪色”或“变淡”的毛色。负责哺乳动物毛发着色的色素由黑素细胞在一种特殊的细胞器——黑素小体内产生。每个黑素细胞负责通过其广泛的树突状分支将黑素小体传递给众多角质形成细胞，这些角质形成细胞进而形成有色素的毛干。在本研究中，我们通过光免疫荧光显微镜和免疫电子显微镜显示，由稀释位点编码的肌球蛋白V同工型与黑素小体相关联。这种关联在所有检测的小鼠黑素细胞系中以及使用两种独立的肌球蛋白V抗体时均可见到，不仅在完全黑素化的细胞中明显，而且在经历黑素小体生物发生过程的细胞中也很明显，在这些细胞中可见到黑素小体标记物和肌球蛋白V分布的协调变化。为了确定已知的基于肌动蛋白的马达蛋白肌球蛋白V可能在黑素小体运输中发挥作用的位置，我们还检测了F-肌动蛋白的细胞分布。肌球蛋白V和F-肌动蛋白都集中的唯一区域是树突和树突尖端，这是黑素小体的唯一目的地，也是它们在培养的黑素细胞中积累的地方。这些结果支持了肌球蛋白V作为黑素小体在树突状延伸内向外移动的马达蛋白的观点，并且，结合关于体外突变黑素细胞表型的现有信息，表明毛色稀释是由这种依赖肌球蛋白V的黑素小体运输系统的缺失引起的。
