Drosophila Mitotic Genes Figure 7. Lack of ZW10 streaming and failure in sister chromatid separation observed after RNAi for genes of the CS3 phenocluster. In merges, DNA is blue and tubulin green. (A) ZW10 does not stream towards the spindle poles in metaphase and remains associated with kinetochores in telophase after RNAi for CG6876 (splicing factor). The ZW10 signal is white in the top panels and red in merges below each of these panels. (B) Cenp-C staining (red in merges) shows that ana-telophase-like figures generated by RNAi to the genes of the CS3 group contain chromosomes that comprise both sister kinetochores. Ctr, control; meta, metaphase; ana, anaphase; telo, telophase. Scale bar, 5 mm. doi:10.1371/journal.pgen.1000126.g007 nocluster also includes Pros26.4, that specifies a proteasome subunit; Klp3A, that encodes a kinesin-like protein; CG4266 and kin17, whose products are conserved proteins implicated in RNA metabolism and the stress response, respectively; and CG3221, that encodes a poorly conserved product of unknown function. The finding that the phenotype elicited by depletion of the APC components is substantially different from that caused by Separase inhibition strongly suggests that the APC/C is required not only for Securin and Cyclin B degradation, but also for the regulation of other aspects of spindle dynamics and spindle-kinetochore interactions. Inactivation of the genes in the CS1–CS5 groups often resulted in very elongated ana/telophase spindles (Figure S8); in some cases, these spindles were twice as long as their counterparts in control cells. Long spindles were often bent or S-shaped, probably due to mechanical constraints imposed by the plasma membrane (Figures S1, S2, S3, S4, S5, S6, S7, and S8). In addition, we observed that the degree of spindle elongation correlates with the presence of scattered chromosomes between the spindle poles. Long spindles have been observed previously in both Drosophila and mammalian cells with defective kinetochores [2,10,37,41], and have been attributed to a misregulation of tubulin addition at the plus ends of kinetochore MTs [2,41]. We observed long ana/ telophase-like spindles in cells containing chromosomes with either functional or nonfunctional kinetochores. Thus, spindle elongation may depend on factors other than kinetochore dysfunction. For example, the chromosomes scattered within the aberrant ana/ telophase figures may induce MT growth and/or stabilization [42], leading to the formation of particularly long spindles. PLoS Genetics | www.plosgenetics.org 9 July 2008 | Volume 4 | Issue 7 | e1000126