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Fig. 4. Cleavage-ring components localise normally in early cytokinesis and are misplaced later in cytokinesis in vibrator mutants. In all panels microtubules are stained green, DNA is blue. Red staining indicates pavarotti, anillin or peanut as indicated. (A,D) Pavarotti. In wild-type spermatocytes (inset in A), pavarotti becomes positioned to a tight band at the midzone of the interdigitating central spindle microtubules at late anaphase and/or telophase (arrowhead). It is also maintained on the ring canals that persist throughout male meiosis (white arrow). Central spindle microtubules appear to be formed correctly in vibrator primary spermatocytes and pavarotti localises correctly within a tight band on the midzone (arrowhead). However, in some cells the central spindle microtubules appear either not to have constricted or to have partially collapsed, and pavarotti is similarly misplaced (yellow arrow). In vibrator secondary spermatocytes in telophase of meiosis II (D), the failure of cytokinesis in the previous meiotic division has resulted in the formation of two secondary spindles within a common membrane. Bipolarity is nevertheless established with two nuclei in each polar position. Pavarotti localises to the mid-zone of this common central spindle. (B,E) Anillin. In wild-type primary spermatocytes (inset in B), anillin concentrates to a tight ring-like structure (arrow) during telophase and is also persistent in ring canals (arrowhead). In vibrator primary spermatocytes, anillin forms a continuous band across the central spindle region of late anaphase (arrow) and can be seen localised as tight rings (arrowhead) in telophase cells (B). In meiosis II, spindles form around two nuclei within a common membrane in vibrator mutants indicating that cytokinesis failed in the previous meiotic division of these cells (E). This panel also shows an example of ring-like canals within the common cell membrane (arrow). These persistent ring-like canals manifest as disorganised, enlarged rings or as scattered or streaked concentrations of anillin (arrowhead). Notice the enlarged diameter of the ring canals compared with those from previous mitotic divisions (compare arrow with asterisk). (C,F) Peanut. Peanut localisation in a ring at the midzone of wild-type primary spermatocytes (inset in C). In most vibrator primary spermatocytes in which the central spindle region has formed correctly, peanut is concentrated as a tight ring structure at the midzone (C). In one cell, peanut is absent from the central spindle midzone, even though the central spindle microtubules appear to have formed correctly (arrow). Cells in which the central spindle microtubules are disorganised have poor peanut localisation (arrowheads). Tetranucleate vibrator cells at telophase of meiosis II (F) in which peanut is present in a single major ring (arrows). Bars, 10 µm.
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