Chromosome-directed oocyte spindle assembly depends HP1 and the Chromosomal Passenger Complex

The chromosomes in the oocytes of many animals appear to promote bipolar spindle assembly. In oocytes, spindle assembly requires the chromosomal passenger complex (CPC), which consists of INCENP, Borealin, Survivin and Aurora B. To determine what recruits the CPC to the chromosomes and its role in spindle assembly, we developed a strategy to manipulate the function and localization of INCENP, which is critical for recruiting the Aurora B kinase. We found that an interaction between Borealin and HP1 is crucial for the initial recruitment of the CPC to the chromosomes and is sufficient to build kinetochores and recruit spindle microtubules. We also found that HP1 moves from the chromosomes to the spindle microtubules along with the CPC, and based on this, propose a mechanism for how the CPC moves from the chromosomes to the microtubules. Within the central spindle, rather than at the centromeres, the CPC and HP1 are required for homologous chromosome bi-orientation.