Chromosomes can congress to the metaphase plate before biorientation

Abstract

The stable propagation of genetic material during cell division depends on the congression of chromosomes to the spindle equator before the cell initiates anaphase. It is generally assumed that congression requires that chromosomes are connected to the opposite poles of the bipolar spindle (i.e., “bi-oriented”). We found that chromosomes can congress before becoming bioriented. By combining the use of reversible chemical inhibitors, live-cell light microscopy and correlative electron microscopy, we found that mono-oriented chromosomes could glide towards the spindle equator alongside kinetochore fibers attached to other already bi-oriented chromosomes. This congression mechanism depended on the kinetochore-associated plus enddirected microtubule motor CENP-E (kinesin-7).