Drosophila Mitotic Genes Figure 10. Mitotic phenotypes observed in the SA1 phenocluster. In merges, DNA is blue and tubulin green. (A) C-metaphase (c-meta) and mitotic figures observed after RNAi for int6. The heterochromatic regions of c-metaphase chromosomes are drastically undercondensed; note also the long astral microtubules in the telophase figures. (B) Extremely contracted chromosomes (c-meta) and short spindles in CG17293 RNAi cells. (C) Examples of short metaphase spindles observed after RNAi for the SA1 genes. (D) pole-to-pole metaphase spindle lengths (mean6SE) observed in the SA1 phenocluster. The average metaphase spindle lengths observed after RNAi for the 17 SA1 genes are all significantly different (with p,0.001 in Student’s t-test) from the average spindle length of control (ctr) metaphases. Scale bars, 5 mm. doi:10.1371/journal.pgen.1000126.g010 phosphatase type 1 (PP1); and the CG6937 product, which is homologous to the human MKI67IP protein that contains an RNA recognition motif and interacts with the Ki-67 mitotic protein (Table S6). The phenotypic differences between DSas-4, cnn or CG17826 RNAi cells (SA3 phenocluster) and those depleted of either Dgrip75 or c tubulin (SA2) are intriguing; they support the view that the latter proteins are not only involved in MT nucleation from the centrosomes but are also required for either MT stability or chromatin and/or kinetochore-induced MT growth [50]. We have included in the SA4 group 4 genes that are essential for spindle assembly but elicit different phenotypic profiles when inactivated by RNAi. Consistent with previous results, RNAi of Klp61F and ncd resulted in monopolar spindles and disorganized bipolar or multipolar spindles, respectively, while Klp67A downreg- ulation led to abnormally long MTs that are unable to interact properly with the kinetochores (Figure 3 and Figure S15; Table S6). The phenotype of cells treated with dsRNA for cdc2 is reminiscent of that of the CS3 phenocluster, with chromosomes that remain congressed in a metaphase plate even when the spindle assumes an ana/telophase configuration. However, cdc2 RNAi cells often show an additional phenotype in which the centrosomes/asters are detached from the spindle poles (Figure 3 and Figure S15). PLoS Genetics | www.plosgenetics.org 12 July 2008 | Volume 4 | Issue 7 | e1000126