Checkpoint arrest after anaphase onset in polo mutants of Drosophila. M.M. Donaldson ^1,2, A.A.M. Tavares ^2,3, H. Ohkura ^2,4, P. Deak ^1,2, D.M. Glover ^1,2, CRC Cell Cycle Genetics Group. 1) Genetics, University of Cambridge, Cambridge, Cambridgeshire, Great Britain; 2) Medical Sciences Institute, University of Dundee, Dundee, Scotland; 3) Department of Chemical Engineering, Instituto Superior Tcnico, Av. Rovisco Pais, Lisboa, and Cell Division Group, Instituto Gulbenkian de Ciencia, Rua Quinta Grande 6, Oeiras, Portugal; 4) The Wellcome Trust Centre for Cell Biology, Institute of Cell and Molecular Biology, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JR, Scotland.

   The Drosophila gene polo encodes a conserved protein kinase known to be required for the organisation of spindle poles and for cytokinesis. Here we report two strongly hypomorphic mutations of polo that arrest cells of the larval brain after the onset of anaphase, in that sister kinetochores are separated by between 20-50% of the total spindle length. Although some sister chromatids appear fully separated, many remain attached either at their centromeric regions or to other chromosomes at their telomeres, and thus are unable to move to the spindle poles. These cells are arrested at the spindle integrity checkpoint; Bub1 protein and the 3F3 epitope are present on the separated kinetochores and the arrest is suppressed by a bub1 mutation. The mutant mitotic spindles are anastral and have assembled upon centrosomes that are associated with centrosomin and the Asp protein, but neither with g-tubulin nor CP190. We discuss roles for polo kinase in recruiting centrosomal proteins and in regulating progression through the metaphase-anaphase transition.