Mouse male meiotic cytokinesis

The final stage of cell division, cytokinesis, cleaves the cytoplasm into two compartments between the separated sister nuclei. This process occurs through the coordinated activities of post-mitotic microtubular structures (midzone or central spindle), the actin-myosin filament system, the midbody and other associated structures. After anaphase, a new class of microtubules is nucleated from the region of the reorganizing daughter nuclei (reviewed by Panteris et al., 1995) towards the cell’s equatorial region. These microtubules plus the interzonal microtubules constitute the midzone spindle. The minus ends of the midzone microtubules are decorated with γ-tubulin (Julian et al., 1993; Shu et al., 1995), indicating that they are dynamic and actively nucleated structures. Their plus-ends interdigitate in the middle (Rattner, 1992), possibly producing a sliding force to move apart the daughter cells (Mullins and Biesele, 1973). Several kinesin-like motor proteins and ‘chromosomal passenger proteins’ move along the midzone spindle towards the plus ends and accumulate in the overlapping region, forming a disc-shaped structure called the telophase disc (reviewed by Andreassen et al., 1991; Margolis and Andreassen, 1993; Savoian et al., 1999). The accumulation of proteins in the overlapping region of the midzone spindle produces a compact and dense structure called the midbody (Rattner, 1992). Other remarkable events of cytokinesis are the ingression of the cortex and the compaction of the midzone spindle, which take place concomitantly with the accumulation of actin and myosin filaments around the equatorial (midbody) region (Sanger et al., 1989; Fukui and Inoue, 1991). The furrow gradually constricts, forming a narrow canal around the midbody and the compact midzone spindle called the intercellular bridge (Mullins and Biesele, 1973). At the final stage of cytokinesis, the intercellular bridge is stretched and severed from both daughter cells and is discarded as a residual body. Our understanding of cytokinesis and its underlying mechanism has been mainly derived from studies done in yeast, Dictyostelium, Drosophila and culture cells. Cytokinesis has not yet been studied in the tissue cells of higher animals. One of the characteristic features of some higher animal tissue systems is the lack of cytokinetic cleavage after nuclear division, resulting in the formation of polykaryons (Clubb and Bishop, 1984; Li et al., 1996). Polykaryons are prevalent in hepatic, muscular and neural tissues. Cytokinesis failure and 4275 Journal of Cell Science 113, 4275-4286 (2000) Printed in Great Britain © The Company of Biologists Limited 2000 JCS1054