Rubin K A, Starodubov S M, Onishchenko G E
Department of Cytology and Histology, Biology Faculty, Moscow State University, Russia.
Cell Mol Biol (Noisy-le-grand). 1999 Nov;45(7):1099-117.
An electron microscopy study showed that in melanophores with dispersed and aggregated pigment the sensitivity of the centrosome and the stability of microtubules were different and depended on the colcemid concentration. The structure of the centrosome didn't change upon exposure to colcemid in dispersed melanophores. In aggregated melanophores, on exposure to 10(-6) M colcemid, the centrosome retained its structure; colcemid at 10(-5)-10(-3) M caused a dramatic collapse of the centrosome. Treatment of aggregated melanophores with colcemid resulted in the complete disassembly of the microtubules; though microtubules in dispersed melanophores appear to be colcemid resistant. Light microscopy studies indicated that in Xenopus melanophores with aggregated or dispersed pigment melanosomes didn't change their location after exposure to 10(-3)-10(-6) M colcemid. Subsequent incubation in colcemid-free medium revealed that the cells retained their ability to translocate melanosomes in response to hormone stimulation. Electron microscopy data revealed the inactivation of the centrosome as MTOC (microtubule-organizing center) in dispersed melanophores with melatonin substituted for MSH in the presence of colcemid. In contrast, with melanocyte-stimulating hormone (MSH) substituted for melatonin, we observed the activation of the centrosome in aggregated cells. We showed that in aggregated melanophores pigment movement proceeded in the complete absence of microtubules, suggesting the involvement of a microtubule-independent component in the hormone-induced melanosome dispersion. However, we observed abnormal aggregation along colcemid-resistent microtubules in dispersed melanophores, suggesting the involvement of not only stable but also labile microtubules in the centripetal movement of melanosomes. The results raise the intriguing questions about the mechanism of the hormone and colcemid action on the centrosome structure and microtubule network in melanophores with dispersed and aggregated pigment.
电子显微镜研究表明，在色素分散和聚集的黑素细胞中，中心体的敏感性和微管的稳定性不同，且取决于秋水仙酰胺的浓度。在色素分散的黑素细胞中，暴露于秋水仙酰胺后中心体的结构没有变化。在色素聚集的黑素细胞中，暴露于10(-6) M秋水仙酰胺时，中心体保持其结构；10(-5)-10(-3) M的秋水仙酰胺会导致中心体急剧解体。用秋水仙酰胺处理色素聚集的黑素细胞会导致微管完全解体；尽管色素分散的黑素细胞中的微管似乎对秋水仙酰胺有抗性。光学显微镜研究表明，在色素聚集或分散的非洲爪蟾黑素细胞中，暴露于10(-3)-10(-6) M秋水仙酰胺后，黑素体的位置没有改变。随后在不含秋水仙酰胺的培养基中孵育发现，细胞保留了响应激素刺激转运黑素体的能力。电子显微镜数据显示，在秋水仙酰胺存在的情况下，用褪黑素替代促黑素细胞激素(MSH)时，色素分散的黑素细胞中的中心体作为微管组织中心(MTOC)失活。相反，用黑素细胞刺激素(MSH)替代褪黑素时，我们观察到聚集细胞中的中心体被激活。我们发现，在色素聚集的黑素细胞中，色素运动在完全没有微管的情况下进行，这表明激素诱导的黑素体分散涉及一个不依赖微管的成分。然而，我们在色素分散的黑素细胞中观察到沿着抗秋水仙酰胺微管的异常聚集，这表明不仅稳定的微管，而且不稳定的微管也参与了黑素体的向心运动。这些结果引发了关于激素和秋水仙酰胺对色素分散和聚集的黑素细胞中中心体结构和微管网络作用机制的有趣问题。
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