fixed cell images were collected by confocal immunofluorescence on a yokogawa csu - x1 spinning disk confocal mounted on a nikon ti - e inverted microscope ( nikon instruments ) . live - cell imaging was performed using a te2000-e2 inverted nikon microscope equipped with the nikon perfect focus system enclosed within a temperature and co2-controlled environment that maintained an atmosphere of 37c and 3 - 5% humidified co2 . sequential facs sorting of tetraploids with 8c dna content was used to generate tetraploid cells with two centrosomes . detailed descriptions of fish , karyotyping , imaging , cell lines , culture conditions , and antibodies used in this study can be found in supplementary methods .
chromosome instability ( cin ) is a hallmark of many tumors and correlates with the presence of extra centrosomes1 - 4 . 
 however , a direct mechanistic link between extra centrosomes and cin has not been established . 
 it has been proposed that extra centrosomes generate cin by promoting multipolar anaphase , a highly abnormal division that produces 3 or more aneuploid daughter cells . here 
 , we use long - term live - cell imaging to demonstrate that cells with multiple centrosomes rarely undergo multipolar cell divisions , and the progeny of these divisions are typically inviable . 
 thus , multipolar divisions can not explain observed rates of cin . 
 by contrast , we observe that cin cells with extra centrosomes routinely undergo bipolar cell divisions , but display a significantly elevated frequency of lagging chromosomes during anaphase . to define the mechanism underlying this mitotic defect , we generated cells that differ only in their centrosome number . 
 we demonstrate that extra centrosomes alone are sufficient to promote chromosome missegregation during bipolar cell division . 
 these segregation errors are a consequence of cells passing through a transient  multipolar spindle intermediate in which merotelic kinetochore - microtubule attachment errors accumulate prior to centrosome clustering and anaphase . 
 these findings provide a direct mechanistic link between extra centrosomes and cin , two common characteristics of solid tumors . 
 we propose that this mechanism may be a common underlying cause of cin in human cancer .