Behnke O, Forer A
University of Copenhagen, Department of Medical Anatomy, Panum Institute, Denmark.
Eur J Haematol Suppl. 1998;61:3-23. doi: 10.1111/j.1600-0609.1998.tb01052.x.
We studied megakaryocyte processes formed in rat bone marrow and spleen, using both the transmission and scanning electron microscopes. Some processes were bulky, others slender and beaded. The bulky megakaryocyte processes developed a specialized arrangement of organelles at the site at which they entered the lumen: filaments present around the outside of the process seemed to support a central cylinder in which organelles flowed along microtubules. Megakaryocyte processes were present in platelet-rich plasma from both human and rat blood. When followed in living preparations, bulky processes developed pointed tips, elongated, and became slender and beaded. Fusiform proplatelets also were present in the platelet rich plasma, with pointed tips at both ends of what appeared to be single "beads"; we assume that the long, beaded megakaryocyte processes would have fragmented were we to have had proper culture conditions. The straight, shorter fusiform proplatelets in living preparations underwent characteristic curving and bending motions, eventually forming disk-shaped cells which sometimes had appendages. This behaviour suggests that the entire process of platelet morphogenesis takes place in plasma: megakaryocyte processes first elongate, then bead and fragment, and then curve and fuse to form disk-shaped platelets. This interpretation is strengthened by finding in freshly isolated plasma many of the shapes seen in the transformations studied in living cell preparations. The megakaryocyte processes and the proplatelets seemed to appear in plasma with a periodicity related to light and dark cycles--that is, with a circadian rhythm. In particular, megakaryocyte processes appear in human blood within a few hours after sunrise; we argue that this might be related to similar peak periods for heart attacks.
我们使用透射电子显微镜和扫描电子显微镜研究了大鼠骨髓和脾脏中形成的巨核细胞突起。一些突起粗大，另一些细长且呈串珠状。粗大的巨核细胞突起在进入管腔的部位形成了细胞器的特殊排列：突起外部周围的细丝似乎支撑着一个中央圆柱体，细胞器沿着微管在其中流动。巨核细胞突起存在于人类和大鼠血液的富含血小板的血浆中。在活体制备物中观察时，粗大的突起会形成尖状末端，伸长，然后变得细长且呈串珠状。富含血小板的血浆中也存在梭形前血小板，在看似单个“珠子”的两端有尖状末端；我们推测，如果有合适的培养条件，长的、呈串珠状的巨核细胞突起会发生碎片化。活体制备物中笔直、较短的梭形前血小板会进行特征性的弯曲和扭转运动，最终形成有时带有附属物的盘状细胞。这种行为表明血小板形态发生的整个过程在血浆中进行：巨核细胞突起首先伸长，然后形成串珠状并碎片化，然后弯曲并融合形成盘状血小板。在新鲜分离的血浆中发现了许多在活细胞制备物研究的转化过程中看到的形状，这一发现强化了这一解释。巨核细胞突起和前血小板似乎以与明暗周期相关的周期性出现在血浆中——也就是说，具有昼夜节律。特别是，巨核细胞突起在日出后几小时内出现在人类血液中；我们认为这可能与心脏病发作的类似高峰期有关。
