It would be particularly interesting to show that phosphorylated KLP61F could interact with Orbit and convey it to the CF site. We showed that Feo, a Drosophila ortholog of PRC1, is also required for Orbit recruitment. Feo is indispensable for the formation of CS MTs and cytokinesis in spermatocytes. It was further reported that mammalian PRC1 is essential for polarizing antiparallel MTs and for concentrating factors for CR assembly. It would be of interest to examine whether Orbit interacts with Feo in CR formation in spermatocytes. On the other hand, CF formation and ingression in Drosophila cultured cells were unaffected by the depletion of Feo, which is essential for the recruitment of Polo to the spindle mid-zone. The indispensability of Polo in cytokinesis differs between cultured cells and spermatocytes. Polo and the KLP3A/Feo complex are particularly PF-3845 important for cytokinesis in spermatocytes. The cellspecific role of the Polo/KLP3A/Feo complex may result from specific characteristics of cytokinesis in germline cells, which are interconnected by cytoplasmic bridges generated from the stabilization of the CR. As both Polo and Orbit continue to be localized on the bridges known as the ring canal, Lapatinib spermatocytes might need this additional regulatory system to stabilize the CR in addition to centralspindlin. Inoue and colleagues reported that the CF ingression of orbit mutant spermatocytes was arrested, and that regression of furrowing occurred at the end. These findings suggest that Orbit also plays an essential role in the later stages of cytokinesis. In the mutant spermatocytes, disintegrated anillin rings and a lack of F-actin rings were described. Since the fixed cells were observed after immunostaining, it could not be distinguished whether these abnormal cells were generated from the failure of CR formation or from collapse of the assembled CR. It is also important to clarify whether Orbit is required for the maintenance of the CR components. Anillin is necessary for the maintenance of actomyosin at the equator in late stages of cytokinesis in Drosophila spermatocytes.