Essential component of the mitotic checkpoint, which prevents cells from prematurely exiting mitosis (PubMed:15886105, PubMed:17576797). Required for the assembly of the dynein-dynactin, Mad2 complexes and spindly/CG15415 onto kinetochores (PubMed:15886105, PubMed:17576797). During cytokinesis in male meiotic cells it is required for completion of cleavage furrow ingression, possibly in conjunction with Rint1 (PubMed:22685323). Required for maintenance of Golgi stack number and morphology, and acroblast assembly (PubMed:22685323). Its function related to the spindle assembly machinery is proposed to depend on its association in the RZZ complex (PubMed:22685323). Failure to assemble the complex due to the absence of any one of its components, results in the incorrect redistribution of the remaining components to diverse membrane compartments (PubMed:22685323). Component of the RZZ complex composed of rod, Zw10 and Zwilch. Dynamic pattern of localization during the cell cycle (PubMed:22685323). Present in structures resembling Golgi stacks prior to their migration into the nuclear zone during prometaphase (PubMed:1339459, PubMed:22685323). At metaphase, detected at the kinetochores and kinetochore microtubules (PubMed:1339459, PubMed:22685323). During anaphase and telophase accumulates at the spindle envelope midzone and broad areas at the cell poles where they often become concentrated in small structures that resemble small Golgi-derived vesicles (PubMed:22685323). In late telophase they also form compact aggregates at the interior of the equatorial region of the cell (PubMed:22685323). Highest levels are found in embryo and adult. Levels decrease during the first and second larval instar and then decrease in third instar larvae and early pupae. In the spermatocytes the number of Golgi structures are reduced and they appear smaller or have collapsed Golgi stacks. In third instar larvae spermatocytes, cytokinesis is abnormal producing multinucleated spermatids with a single large Nebenkern. Acroblasts do not form and instead appear as an aggregate of multiple unfused vesicles. During anaphase and early-telophase the central spindle appears regular and acto-myosin contractile rings form normally but during mid-telophase the rings fail to constrict. By late-telophase the rings become fragmented, and the central spindle appears less dense, is irregularly shaped and eventually disassembles. Spermatocytes are unable to complete furrow ingression due to reduced plasma membrane formation during cytokinesis. Belongs to the ZW10 family. It is uncertain whether Met-1, Met-44, Met-81 or Met-100 is the initiator.