Optogenetic Control of Spindle Microtubule Crosslinkers Reveals that Bridging Fibers Promote Chromosome Alignment by Overlap Length-Dependent Forces

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