Blood platelets are assembled principally at the ends of proplatelet processes produced by differentiated megakaryocytes.
Blood platelets are assembled principally at the ends of proplatelet processes produced by differentiated megakaryocytes.
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DOI：
10.1083/jcb.147.6.1299
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发表时间：
1999-12-13
影响因子：
7.8
通讯作者：
Hartwig, J H
中科院分区：
文献类型：
--
作者：
Italiano, J E Jr;Lecine, P;Shivdasani, R A;Hartwig, J H
巨核细胞通过复杂的过程释放成熟的血小板。众所周知，血小板是从称为前血小板的中间结构中释放出来的，它是巨核细胞细胞质的长管状延伸。我们已经解析了前血小板形态发生特定阶段巨核细胞细胞骨架的超微结构，并将这些结构与视频显微镜定义的细胞质重塑事件相关联。血小板的产生始于大伪足的延伸，伪足使用独特的皮质微管束来拉长并形成具有球状末端的薄前血小板过程；它们包含外围的微管束，这些微管束自身缠绕并形成泪滴状结构。与之前的观察和假设相反，延时显微镜揭示前血小板过程是极其动态的结构，可以在扩散形式和管状形式之间可逆地相互转换。类似于在血小板中观察到的微管线圈仅在前血小板末端检测到，而不是在沿着前血小板延伸长度发现的血小板大小的珠子内检测到。前血小板过程的生长和延伸与反复弯曲和分叉相关，这导致自由端的显着放大。这些方面受到细胞松弛素 B 的抑制，因此依赖于肌动蛋白。我们提出，成熟血小板从头组装并仅在前血小板末端释放，并且在前血小板形态发生过程中观察到的复杂弯曲和分支代表了增加前血小板末端数量的优雅机制。
Megakaryocytes release mature platelets in a complex process. Platelets are known to be released from intermediate structures, designated proplatelets, which are long, tubelike extensions of the megakaryocyte cytoplasm. We have resolved the ultrastructure of the megakaryocyte cytoskeleton at specific stages of proplatelet morphogenesis and correlated these structures with cytoplasmic remodeling events defined by video microscopy. Platelet production begins with the extension of large pseudopodia that use unique cortical bundles of microtubules to elongate and form thin proplatelet processes with bulbous ends; these contain a peripheral bundle of microtubules that loops upon itself and forms a teardrop-shaped structure. Contrary to prior observations and assumptions, time-lapse microscopy reveals proplatelet processes to be extremely dynamic structures that interconvert reversibly between spread and tubular forms. Microtubule coils similar to those observed in blood platelets are detected only at the ends of proplatelets and not within the platelet-sized beads found along the length of proplatelet extensions. Growth and extension of proplatelet processes is associated with repeated bending and bifurcation, which results in considerable amplification of free ends. These aspects are inhibited by cytochalasin B and, therefore, are dependent on actin. We propose that mature platelets are assembled de novo and released only at the ends of proplatelets, and that the complex bending and branching observed during proplatelet morphogenesis represents an elegant mechanism to increase the numbers of proplatelet ends.