Melanosomes are motile, light-absorbing organelles that are present in pigment cells of the skin and eye. It has been proposed that melanosome localization, in both skin melanocytes and the retinal pigment epithelium (RPE), involves melanosome capture from microtubule motors by an unconventional myosin, which dynamically tethers the melanosomes to actin filaments. Recent studies with melanocytes have questioned this cooperative capture model. Here, we test the model in RPE cells by imaging melanosomes associated with labeled actin filaments and microtubules, and by investigating the roles of different motor proteins. We found that a deficiency in cytoplasmic dynein phenocopies the lack of myosin-7a, in that melanosomes undergo fewer of the slow myosin-7a-dependent movements and are absent from the RPE apical domain. These results indicate that microtubule-based motility is required for the delivery of melanosomes to the actin-rich apical domain and support a capture mechanism that involves both microtubule and actin motors.

黑素体是存在于皮肤和眼睛色素细胞中的活动的、吸光的细胞器。有人提出，皮肤黑素细胞和视网膜色素上皮 (RPE) 中的黑素体定位涉及非常规肌球蛋白从微管马达捕获黑素体，该肌球蛋白动态地将黑素体束缚在肌动蛋白丝上。最近对黑素细胞的研究对这种合作捕获模型提出了质疑。在这里，我们通过对与标记的肌动蛋白丝和微管相关的黑素体进行成像，并通过研究不同运动蛋白的作用来测试 RPE 细胞中的模型。我们发现细胞质动力蛋白的缺陷与肌球蛋白 7a 的缺乏相似，因为黑素体经历较少的缓慢的肌球蛋白 7a 依赖性运动，并且在 RPE 顶端域中不存在。这些结果表明，将黑素体递送至富含肌动蛋白的顶端域需要基于微管的运动，并支持涉及微管和肌动蛋白马达的捕获机制。