During metaphase, chromosome position at the spindle equator is regulated by the forces exerted by kinetochore microtubules and polar ejection forces. However, the role of forces arising from mechanical coupling of sister kinetochore fibers with bridging fibers in chromosome alignment is unknown. Here we develop an optogenetic approach for acute removal of PRC1 to partially disassemble bridging fibers and show that they promote chromosome alignment. Tracking of the plus-end protein EB3 revealed longer antiparallel overlaps of bridging microtubules upon PRC1 removal, which was accompanied by misaligned and lagging kinetochores. Kif4A/kinesin-4 and Kif18A/kinesin-8 were found within the bridging fiber and largely lost upon PRC1 removal, suggesting that these proteins regulate the overlap length of bridging microtubules. We propose that PRC1-mediated crosslinking of bridging microtubules and recruitment of kinesins to the bridging fiber promotes chromosome alignment by overlap length-dependent forces transmitted to the associated kinetochore fibers.

中文翻译：

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PRC1的光遗传学控制通过重叠长度依赖性力揭示了其在纺锤体染色体排列中的作用

在中期，纺锤体赤道的染色体位置受着丝粒微管施加的力和极地喷射力的调节。然而，姐妹动粒纤维与桥接纤维在染色体排列中的机械耦合所产生的力的作用尚不清楚。在这里，我们开发了一种用于急性去除 PRC1 以部分分解桥接纤维并显示它们促进染色体对齐的光遗传学方法。对加端蛋白 EB3 的跟踪显示，在去除 PRC1 后，桥接微管的反平行重叠更长，这伴随着错位和滞后的动粒。在桥接纤维中发现了 Kif4A/kinesin-4 和 Kif18A/kinesin-8，并且在去除 PRC1 后大部分丢失，表明这些蛋白质调节桥接微管的重叠长度。