Biol. Cell (2007) 99, 627–637 (Printed in Great Britain) doi:10.1042/BC20070047 Research article Dynein participates in chromosome segregation in fission yeast Thibault Courtheoux, Guillaume Gay, C ´ eline Reyes, Sherilyn Goldstone, Yannick Gachet 1 and Sylvie Tournier 1 LBCMCP-CNRS UMR5088, Institut d’Exploration, Fonctionelle des G ´ enomes (IFR109), Universit ´ e Paul, Sabatier, 118 route de Narbonne, 31062 Toulouse, France Background information. In eukaryotic cells, proper formation of the spindle is necessary for successful cell division. For faithful segregation of sister chromatids, each sister kinetochore must attach to microtubules that extend to opposite poles (chromosome bi-orientation). At the metaphase–anaphase transition, cohesion between sister chromatids is removed, and each sister chromatid is pulled to opposite poles of the cell by microtubule-dependent forces. Results. We have studied the role of the minus-end-directed motor protein dynein by analysing kinetochore dy- namics in fission yeast cells deleted for the dynein heavy chain (Dhc1) or the light chain (Dlc1). In these mutants, we found an increased frequency of cells showing defects in chromosome segregation, which leads to the appearance of lagging chromosomes and an increased rate of chromosome loss. By following simultaneously kinetochore dy- namics and localization of the checkpoint protein Mad2, we provide evidence that dynein function is not necessary for spindle-assembly checkpoint inactivation. Instead, we have demonstrated that loss of dynein function alters chromosome segregation and activates the Mad2-dependent spindle-assembly checkpoint. Conclusions. These results show an unexpected role for dynein in the control of chromosome segregation in fission yeast, most probably operating during the process of bi-orientation during early mitosis. Introduction In all eukaryotes, faithful sister chromatid segreg- ation is a key event in the maintenance of genetic integrity. For high-fidelity chromosome segregation, kinetochore attachment to the spindle microtubules is essential and requires microtubule function during mitosis. The capture of the kinetochores by microtubules is an early step in mitosis, when the chromosomes are found in close proximity to one of the spindle poles (Maiato et al., 2004; Tanaka et al., 2005). This process has been visualized in very few cell types, in- cluding the asymmetrically dividing budding yeast (Merdes and De Mey, 1990; Rieder and Alexander, 1 To whom correspondence should be addressed (email gachet@cict.fr or tournier@cict.fr). Key words: chromosome segregation, dynein, fission yeast, kinetochore, Mad2, spindle checkpoint. Abbreviations used: Atb2, α2-tubulin; CFP, cyan fluorescent protein; Dhc, dynein heavy chain; Dlc, dynein light chain; GFP, green fluorescent protein; Myo2, type II myosin; SAC, spindle-assembly checkpoint; SPB, spindle pole body. 1990; Tanaka et al., 2005). In these studies, it was es- tablished that the kinetochores are initially captured by the lateral surface of a single microtubule extend- ing from the spindle pole. The captured kinetochores are then transported poleward to the spindle pole where each sister kinetochore eventually attaches to the plus ends of microtubules, extending from the opposite spindle pole (Merdes and De Mey, 1990; Rieder and Alexander, 1990; Tanaka et al., 2005). In the following stage, the chromosomes align at the metaphase plate, which is formed equidistant between the centrosomes. Congression to the meta- phase plate is generated by forces produced by the chromokinesins and kinetochore-bound molecular motors, such as the mitotic kinesins. It has also been suggested that chromosome congression is driven by minus-end-directed motors, which can pull the kin- etochores from one pole to the opposite one (Savoian et al., 2000; Sharp et al., 2000). In all eukaryotic cells, progression through the cell cycle is monitored by a series of checkpoints that ensure both the fidel- ity and the temporal and spatial order of cell cycle www.biolcell.org | Volume 99 (11) | Pages 627–637 627